Ruthanne Hyduke, M.A.*
Part II. The Urine Microscopic Examination
Ruthanne Hyduke, M.A.
1. Describe how to prepare the sample for microscopic analysis
2. Outline the ways to standardize the microscopic urinalysis (quality control)
3. Describe how to view the urine and count the elements.
4. Identify the most common elements including artifacts found in the urine sediment.
5. Identify the elements of urine sediment found in advanced stages of disease.
Introduction
The third part of the urinalysis is the microscopic examination
of the urine sediment. Its careful study will present clues to the
ultimate diagnosis of a variety of systemic diseases and urinary
tract disorders. The elements in the urine can originate from the
blood, the kidney, the lower urinary tract, and external
contamination; it becomes important to be able to differentiate the
sources of the elements. At one time, microscopic examinations were
routinely analyzed on every urine that came into the laboratory. To
control costs, many of today's laboratories perform the microscopic
only on those urines that show some abnormalities on the physical and
chemical analysis, those that come from patients with known renal
disease, or those where the physician specifically requests a
microscopic regardless of the other results.
As with other laboratory analyses, quality control is a very important part of the microscopic examination. The microscopic QC consists of standardizing the way the microscopic is performed by centrifuging the same amount consistently and then examining an exact of the sediment quantity (determined by the slide provided or by pipetting the quantity with a automatic pipettor) each time the test is performed. At this time the best way to standardize the process is to use one of the three commercial systems that are currently available. Should the expense of these systems be prohibitive, then the procedure described below will provide an alternative way of being consistent in performing the analysis.
Tubes,
pipets and slides used for standardizing urine sediments
The urine most likely to show formed elements is the first morning specimen. Like the chemical analysis, the urine must be collected by the midstream or clean catch technique. In males the glans penis should be cleansed using cotton moistened with sterile saline. The patient is instructed to void discarding the first portion of the void, collecting the middle part and discarding the final portion. (This would be similar to voiding into three containers where the middle container is retained for analysis.) The female patient is instructed to separate the labia and wash the urethral orifice with several single downward strokes using sterile moistened cotton and then collect the urine with the labia still separated.
The urine must be collected in a clean, sterile if a culture is being performed, container free from fibers, talc and other contaminants. All urine collections must avoid contamination with menstrual blood, vaginal secretions and feces. The patient will be asked to collect another sample if any contamination is found. (Because contaminants are commonly found in the urine, the experienced microscopist must become as familiar with them as the true urine elements.) The microscopic examination must be analyzed immediately or refrigerated for not more than four hours. The elements in the urine change rapidly when the urine stands at room temperature for any length of time.
Ruthanne Hyduke, M.A.
Ruthanne Hyduke, M.A.
Centrifuge
tube
Centrifuge
tube with pipet
After centrifugation, remove the supernatant fluid with a
polyethylene, transfer pipet leaving 0.5 to 1.0 mL urine on the
sediment. Each laboratory should define the quantity left on the
sediment. The commercial systems use decanting methods where 0.4, 0.8
or 1.0 mL urine is left on the sediment. This is an important point
of the standardization of the examination. Resuspend the sediment in
the remaining urine by flicking the bottom of the tube or by running
the tube across a test tube rack.
Pipet
filling chamber on slide
Using a plastic or polypropylene transfer pipet, mount a drop of the
urine in the counting chamber of the prepared, commercial plastic
slides. Glass slides and coverslips are not recommended because they
do not produce reliable, consistent results. However, if your
laboratory uses them, then pipet an exact volume, e.g. 20 µl,
onto the slide using an automatic pipet and polypropylene tip. Avoid
using glass pipets when mounting the urine sediment as elements like
casts tend to cling to the glass surface. After counting the elements
in the sediment, you may calculate the number of elements per
milliliter. In situations where less urine is centrifuged or a
greater quantity is left on the sediment, the count may need to be
adjusted through calculation so that you consistently report the
number of elements per standard quantity (the amount of sediment that
you are examining).
Special stains can be used to enhance the elements in the sediment. Many commercial stains can be purchased; however, stains often become contaminated and interfere with accurate identification of the urine elements. Supravital stains such as the Sternheimer-Malbin stain (crystal-violet and safranin) and toluidine blue will enhance the internal structures of the cells making them easier to identify. Acetic acid may be added to the sediment to enhance the nuclear pattern of white blood cells and to lyse the red blood cells. The latter is helpful in differentiating yeast from red blood cells. Fat or lipid stains like Oil Red O can be used to confirm the presence of fat droplets or triglycerides suspected in the urine. Many laboratories prefer to routinely observe the sediment without any stain and only add one to confirm the identification of some elements.
The urine is examined microscopically using bright field, phase contrast or polarized light. The best microscope to use to identify hyaline casts is the phase contrast microscope. However, it is not cost-effective to purchase this specialized equipment. When using a bright field microscope, adjust the light so that it is very dim by racking the condenser down, closing the diaphragm and keeping the rheostat at its lowest setting. It is often very helpful to find a squamous epithelial cell on which to focus so that you are certain that you are focused in the urine sediment and not in another plane. Scan the edge of the coverslip first on low power to look for and count casts. You may need to confirm their identification on high power. Then move to the center of the coverslip and use the high power objective to identify and count the cells and other elements. To semiquantitate the elements, average the number seen in 20 fields (10 low power, 10 high power) of the urine. Crystals are identified and counted only if they are abnormal crystals. However, mentally noting normal crystals provides a cross-check on the pH of the urine. Abnormal crystals are confirmed by using polarized light or by chemical testing.
Ruthanne Hyduke, M.A.
Mix the urine well and pour 12 milliliters of urine in a clean centrifuge tube. (The physical and chemical analysis can be performed on the urine in the tube before centrifuging or on the urine left in the collection container while the tube is centrifuging.) Cap the tube and centrifuge the urine for five minutes at 450 g. RPMs for different centrifuges can be determined by consulting the nomogram in the manufacturer's manual that comes with the centrifuge. At this speed the sediment will be optimally concentrated without destroying any of the fragile elements in the urine.
Ruthanne Hyduke, M.A.
After centrifugation, remove the supernatant fluid with a polyethylene, transfer pipet leaving 0.5 to 1.0 mL urine on the sediment. Each laboratory should define the quantity left on the sediment. The commercial systems use decanting methods where 0.4, 0.8 or 1.0 mL urine is left on the sediment. This is an important point of the standardization of the examination. Resuspend the sediment in the remaining urine by flicking the bottom of the tube or by running the tube across a test tube rack.
Ruthanne Hyduke, M.A.
Using a plastic or polypropylene transfer pipet, mount a drop of the urine in the counting chamber of the prepared, commercial plastic slides. Glass slides and coverslips are not recommended because they do not produce reliable, consistent results. However, if your laboratory uses them, then pipet an exact volume, e.g. 20 µl, onto the slide using an automatic pipet and polypropylene tip. Avoid using glass pipets when mounting the urine sediment as elements like casts tend to cling to the glass surface. After counting the elements in the sediment, you may calculate the number of elements per milliliter. In situations where less urine is centrifuged or a greater quantity is left on the sediment, the count may need to be adjusted through calculation so that you consistently report the number of elements per standard quantity (the amount of sediment that you are examining).
Special stains can be used to enhance the elements in the sediment. Many commercial stains can be purchased; however, stains often become contaminated and interfere with accurate identification of the urine elements. Supravital stains such as the Sternheimer-Malbin stain (crystal-violet and safranin) and toluidine blue will enhance the internal structures of the cells making them easier to identify. Acetic acid may be added to the sediment to enhance the nuclear pattern of white blood cells and to lyse the red blood cells. The latter is helpful in differentiating yeast from red blood cells. Fat or lipid stains like Oil Red O can be used to confirm the presence of fat droplets or triglycerides suspected in the urine. Many laboratories prefer to routinely observe the sediment without any stain and only add one to confirm the identification of some elements.
The urine is examined microscopically using bright field, phase contrast or polarized light. The best microscope to use to identify hyaline casts is the phase contrast microscope. However, it is not cost-effective to purchase this specialized equipment. When using a bright field microscope, adjust the light so that it is very dim by racking the condenser down, closing the diaphragm and keeping the rheostat at its lowest setting. It is often very helpful to find a squamous epithelial cell on which to focus so that you are certain that you are focused in the urine sediment and not in another plane. Scan the edge of the coverslip first on low power to look for and count casts. You may need to confirm their identification on high power. Then move to the center of the coverslip and use the high power objective to identify and count the cells and other elements. To semiquantitate the elements, average the number seen in 20 fields (10 low power, 10 high power) of the urine. Crystals are identified and counted only if they are abnormal crystals. However, mentally noting normal crystals provides a cross-check on the pH of the urine. Abnormal crystals are confirmed by using polarized light or by chemical testing.
Ruthanne Hyduke, M.A.
Microorganisms
The most common microorganisms found in the urine are yeast and
bacteria. Trichomonas may also be found as a contaminant in females
who have a vaginal infestations.
Casts
Urine casts are cylindrical, cigar-shaped
bodies that represent molds or "casts" of the lumen of the renal
tubule in which they were formed. They are the only urine element
that is truly unique to the kidney. Although there are several
different casts that may be seen in urine, the common matrix of all
casts is a mucoprotein known as Tamm-Horsfall protein which is
secreted by the renal tubule at a fairly constant rate.
Crystals
Crytals form as the urine cools to room temperature and the
concentrated solutes precipitate out of the urine. The urine pH
influences which crystals are formed. Most crystals are not
clinically significant; and if the urines are not analyzed
immediately, crystals will be present.
Miscellanous Elements and Artifacts
Many miscellaneous elements can be found in the urine, some of which
may be significant, but most are not. In addition, the urine can be
easily contaminated from improper collection of the urine sample or
collecting in a dirty sample container. The experienced microscopist
easily differentiates these from the significant elements. However,
they can be very frustrating to the novice because so many look like
other elements or they fit the descriptions given for other elements.
For this reason, it is wise to become very familiar with all of the
artifacts as well.
Ruthanne Hyduke, M.A.
Squamous epithelial cells are large (40 - 60 µm), flat, irregularly-shaped cells with abundant cytoplasm and a small round nucleus. The cell edge is often folded or the cell may be rolled into a cylinder. (The latter can be confused with a cast!) These cells originate in the superficial layers of the vagina, vulva or urethra and are the least significant of the cells seen in the sediment. Small numbers of squamous epithelial cell are seen in most urines. Large numbers in the urine of a female suggest that the urine has been contaminated with vaginal secretions.
This image provides a good example of two unstained squamous epithelial cells. Note the size of the cell, its nucleus and its irregular shape. These two cells look somewhat granular which is an artifact of the urine preservation.
Ruthanne Hyduke, M.A.
Transitional epithelial cells are a little smaller than squamous epithelial cells ( 20 - 40 µm). They can vary in size depending on the origin of the cell, but are very regularly (smoothly) shaped. The shapes vary from round with a tail-like process to pear-shaped. They have a round, centrally-located nucleus which appears small in relation to the overall size of the cell. In cases of urinary tract infections, increased numbers of transitional epithelial cells can be seen. Sheets or clusters of cells indicate that the patient has undergone some instrumental procedure like catheterization. Transitional cells have the ability to absorb water which causes them to be very round and appear larger than a squamous epithelial cell.
This field shows a transitional epithelial cell at "B". The three cells just above this one are also transitional epithelials. "A" points to a squamous epithelial cell.
Ruthanne Hyduke, M.A.
Under high power unstained red blood cells appear as pale, homogeneous, biconcave discs with no nucleus. They vary somewhat in size, but are usually about 7 µm in diameter. If the specimen is not fresh when it is examined, the cells will appear as faint, colorless circles (shadow or ghost cells) because the hemoglobin has leached out of the cell. In urine with a very high specific gravity the red cells become crenated which may appear as granules or spikes in the cell. In urine with a low specific gravity or with extreme pHs, the cells may be completely lysed and not visible. Red cells "tumble" when the fluid on the slide is set in motion. Physiological increases in the number of red blood cells in urine may occur following violent exercise or fever without indicating significant urinary tract disease. Presence of large numbers of red cells (smoky urine) indicates bleeding into the urinary tract anywhere from the glomeruli to the urethra. This may be due to several causes from trauma to severe renal disease. The presence of red cells without the presence of protein or casts indicates that the bleeding occurred lower than the kidney. Dysmorphic (distorted) red cells indicate that the bleeding has occurred in the glomerulus. The presence of the red cells in the sediment can be correlated with the physical and chemical analysis of the urine. If the results do not correlate, further investigation is recommended.
There are many RBCs in this field. Note the center pallor of most of the cells especially the one labeled with a "B". Can you picture the donut shape or biconcave disc form of the cell? "A" points to a red cell on its side.
This is another field of RBCs. Note that some of them look granular. That is because they are crenated or puckered. The spicules make the cell look granular..
Ruthanne Hyduke, M.A.
Under high power, white blood cells (leukocytes) appear as round granular spheres about 14 µm in diameter (about twice the size of a red cell) and have a nucleus. To enhance the nucleus, 10% acetic acid can be added to the sediment which will outline the nucleus for better observation. Because neutrophils have a lobed nucleus, they may look as though they have more than one nucleus although the granules may make it hard to distinguish. The lymphocyte has a round nucleus and no granules. Do not attempt to differentiate the white cells in the urine unless special procedures are performed.
Some white cells are larger than usual because they have absorbed water, and the cytoplasmic granules exhibit Brownian movement. These cells are classified as "glitter" cells and are a result of a hypotonic urine.
White cells can gain access to the urine from any locus along the genitourinary tract, and a few can be found in normal centrifuged urine. Pyuria or many white cells in the urine generally indicates a suppurative process somewhere in the kidney (pyelonephritis), bladder (cystitis) or urethra (urethritis). Clumps of white cells are often found in the presence of bacteria and may indicate the presence of pyelonephritis. Clumping is noted because it affects the white cell count.
The presence of increased numbers of eosinophils may be indicative of drug-induced interstitial nephritis. However, special staining procedures using Hansel's stain must be performed before the eosinophils can be identified.
Lymphocytes in the urine cannot be clearly identified without the use of a Wright's or Papanicolaou stain. The presence of lymphocytes may indicate renal transplant rejection. Because lymphs do not contain leukocyte esterase, they will not react with the reagent strip reaction for white cells.
In this field, "C" points to a white cell and "B" points to two transitional epithelial cells. Note that you can distinguish a nucleus in the white cell if you look very closely. Also note the granular appearance.
Ruthanne Hyduke, M.A.
Yeast cells can be mistaken for red blood cells since they have a double refractile wall which may simulate the donut appearance of red cells. However, yeast cells tend to be smaller, more oval than round, variable in size, colorless and usually show budding. Because they are refractile, they will shine brightly when moving in and out of focus. They will not lyse when 10% acetic acid is added to the urine. Mycelial or pseudohyphae strands may also be seen along with the yeast cells.
Yeast may be due to a true urinary tract infection or to contamination of the urine with vaginal secretions. Their presence could also indicate contamination from the air or the skin surface such as from the hands.
This frame shows an excellent example of yeast ("B"). Note the budding and the more oval appearance of each cell. ("A" is a crenated red blood cell; "C" is also a red cell.)
Ruthanne Hyduke, M.A.
These microorganisms vary in size from long, thin to short, plump rods to cocci. They often appear motile in a fresh urine preparation. If found with white blood cells, the bacteria indicate an infection in the urinary tract. If bacteria are found without white cells, the laboratorian must investigate the collection and handling procedures. Bacteria found in the urine microscopic examination are reported as few, moderate or many and are not further identified. If pyelonephritis is suspected, a urine culture is indicated.
The novice microscopist may confuse bacteria with red cells because as the bacteria go out of focus they seem to enlarge and become round. However, red cells are many times larger than bacteria.
This is an excellent example of a mixed field of red blood cells and bacteria. "C" is pointing to the bacteria. Note how small they are compared to the RBC.
Ruthanne Hyduke, M.A.
Trichomonas vaginalis is the most common parasite in urine in the United States and is found in approximately 25% of women in casual vaginal cervical examination. The presence of this organism in urine specimens of females is due to the contamination of the urine with vaginal secretions. Males are asymptomatic carriers and the organisms may be found in prostatic fluid.
Under bright-field microscopy, Trichomonas vaginalis appears pear shaped when viewed from the side and round when seen from above or below. They are slightly larger than white blood cells. These protozoans are actively motile in fresh urine specimens due to the presence of four anterior flagella and an undulating membrane, all of which may be difficult to see. They are often discovered due to the convection currents they cause in the sediment on the slide. They can be confused with both white cells and renal tubular cells; but their motility will help distinguish them. For that reason, very fresh urine samples must be analyzed.
It is difficult to distinguish trichomonads in pictures or in urine that sat too long. It's much more fun to see them swimming in a fresh urine sample.
Ruthanne Hyduke, M.A.
Because Tamm-Horsfall protein is a globulin, the reagent strip analysis of the urine does not detect this protein. As the urine in the tubules becomes concentrated, as urine stasis occurs or when the pH is very low, the protein forms fibrils that attach to the lumen cells. The fibrils intertwine to eventually form the cast itself which is washed out into the urine as flow increases. While the fibrils intertwine, they may entrap other chemicals or elements that are present in the urine.
Casts vary in length and thickness, but the diameter is uniform throughout the length of each cast. The sides are parallel and the ends are rounded in the unbroken structures. The cylindrical shape of casts is shown by their rolling effect when the urine under the cover slip moves. The refractive index of casts, especially hyaline casts, is similar to that of the urine itself. For this reason they are frequently difficult to see and very subdued light is required.
Hyaline are the least significant of the casts and a few can be found in the urine of normal individuals after physical exertion, emotional stress or febrile diseases. They are colorless, homogeneous, and semi-transparent. Because of their low refractive index, the best microscopy to use is phase-contrast which enhances their visibility. However, these microscopes add costs to the analysis of the urine. While most hyaline casts are cigar-shaped, those formed in the Loop of Henle may have a tapered tail on one end. These are called cylindroids and have the same significance as hyaline casts. In disease states as many as 30 hyaline casts per low power field is common. Hyaline casts dissolve quite readily in alkaline urine.
This is an almost perfect example of a hyaline cast (arrow). Note its cigar shape and how difficult it is to see because it blends into the background. Also note the mucus threads that are scattered throughout and the squamous epithelial cell in the lower left corner.
Ruthanne Hyduke, M.A.
Acid Urine pH |
Neutral Urine pH |
Alkaline Urine pH |
Calcium Oxalate |
Ammonium Biurate |
Triple Phosphates |
Uric Acid |
Calcium Carbonate |
Ammonium Biurate |
|
Calcium Oxalate |
Calcium Carbonate |
|
Triple Phosphate |
Calcium Phosphate |
Amorphous urates |
|
Amorphous Phosphates |
Many laboratories do not report the presence of the normal crystals unless they are present in very large quantities.
This image provides a good example of calcium oxalate. Note the refractile, square, "envelope" shape with a refractile "X" in the center. They can vary in size from needing high power magnification in order to see them to being readily recognizable on low power. "B" is pointing to amorphous sediment that precipitates upon rapid cooling of any urine.
This image provides a good example of uric acid. These crystals can take multiple forms: "A" is one of the rhombic plate (diamond-shaped) and is very common. "B" is the uric acid crystal in the shape of a barrel. They are often yellow to orange-brown in color. Under polarized microscopy they exhibit birefringence and many colors.
The presence of very large numbers of uric acid crystals may accompany gout and conditions of increased purine metabolism as in chemotherapy.
The image at the arrow provides a good example of triple phosphate. Note the colorless, "coffin-lid" appearance. Some forms may take a fern-like or prism appearance. While seen mostly in normal urines, they may accompany urinary tract infections (UTIs) associated with an elevated pH.
Ruthanne Hyduke, M.A.
This frame shows a field covered with wavy mucus threads. Can you identify the crystals at "B" and "C" or the cell almost in the center of the field?
Ruthanne Hyduke, M.A.
This frame shows a good example of sperm ("B"). Note the oval head and long tail. Sometimes the heads may look like yeast. When viewing a urine sediment, focus carefully to see the tails. Also note the RBC at "A".
Ruthanne Hyduke, M.A.
Starch granules appear in the urine from body powders or the talc from examination gloves. They can be confused with fat globules in the urine because they also form the Maltese cross pattern under polarized light. However, starch granules are not refractive under bright field microscopy and usually have an indented center. They are not round, but appear to have a scalloped edge. Because they are a contaminant, they are not reported. Note the puckered centers and irregular shapes of these starch or talc crystals.
Oils and creams from lotions and lubricants may be introduced during specimen collection. They can also be introduced into the urine from a dirty microscope oil immersion objective. They resemble fat droplets that are truly part of the urine, but look very homogeneous, lack structure and often coalesce. They may resemble the oil droplets described in the next section.
Many kinds of fibers such as hair and fabric threads appear in the urine. The novice microscopist tends to confuse them with casts. However, hair and fibers have very dark, harsh-looking outlines (casts have outlines that blend into the background). They are often moderately refractile and can be very large. Fibers are flat (casts are cylindrical) and thicker at the margins (casts are thicker in the middle). Fibers will polarize light; casts will not. Because fibers and hair are a contaminant, they are not noted. "A" points to a typical fiber. Note that the edges are very dark and the surface has unusual striations on it.
Pollen can be found in urine during growing seasons and can have a variety of shapes and forms. They often look like crystals with concentric circles, are very large, and often look out of focus when the other urine elements are in focus.
Becoming familiar with the elements above can help eliminate frustration when beginning to view urine sediments. Beginners often begin to think that a sediment only contains contaminants because they are so apparent and numerous. The more experience one gets with looking at urine sediments the easier it is to ignore all of the insignificant and confusing elements found there.
Ruthanne Hyduke, M.A.
Renal
Tubular Epithelial Cells
Fat
Globules and Oval Fat Bodies
Ruthanne Hyduke, M.A.
Renal tubular epithelial cells (RTC) are round cells about the size of a white blood cell (15 µm in diameter). They contain a single large nucleus usually located eccentrically. Increased numbers of renal tubular cells indicates necrosis of the tubules. They are present in pyelonephritis, toxic reactions, viral infections, allograft rejection and the secondary effects of glomerulonephritis. They can contain absorbed pigments like bilirubin or non lipid filled vacuoles. In addition they can absorb lipids and are then called oval fat bodies.
With much experience, the skilled technologist can begin to identify the cells from different parts of the tubules. Convoluted renal tubular cells often have coarsely granular cytoplasm and may look like granular casts. Proximal convoluted tubular cells are much larger than white cells and usually oblong in shape. The distal convoluted tubular cells are round to oval and smaller than the proximal convoluted tubular cells. Both of these cells are the result of acute ischemic or toxic renal tubular disease.
The collecting duct cells are never round but cuboidal or columnar in shape. They characteristically have one straight edge which must be evident before identifying it. In addition, collecting duct cells may be found in "sheets" or fragments of undisrupted tubular epithelium. The presence of the sheets indicate ischemic necrosis of the tubular epithelium following shock or sepsis. Single cells will be found in nephritis, acute tubular necrosis, kidney transplant rejection and salicylate poisoning.
This frame compares a WBC ("B") and an RTC ("A"). Note the size comparison. Also note how prominent the nucleus is in the RTC. It is much easier to see than the nucleus of the WBC.
Ruthanne Hyduke, M.A.
Oval fat bodies can be found in the urine of individuals with a wide variety of nephropathies and probably indicate extensive tubular degeneration. They are almost always present in patients with the nephrotic syndrome and accompanied by severe proteinuria.
This frame shows an oval fat body ("B") next to several transitional epithelial cells ("A"). Note the drops of lipids that appear to be contained within the cell.
This shows the typical Maltese cross pattern that oval fat bodies display under polarized light.
Free floating fat globules vary in size and appear light yellow or brown. They are highly refractile. These fats can be differentiated into cholesterol and triglycerides by staining with Oil Red O which causes the triglycerides to stain orange or red while cholesterol remains clear. Lipiduria is always clinically significant.
Ruthanne Hyduke, M.A.
While a few hyaline casts can be found in urine from normal individuals, extensive numbers will indicate some renal disease. The following casts are also clinically significant. If you do not remember how casts are formed, go back to Part IIB and review the section on casts. Recall that casts vary in length and thickness; but the diameter is uniform throughout the length of each cast, the sides are parallel, and the ends are rounded. Think cigar-shaped when looking for casts.
As the fibrils of the cast form, the most common elements in the urine can become entrapped within the matrix. Cellular casts will have at least three identifiable cells within the matrix; and if the cells can be further identified, the cast will be called by that cell name. As the cells in the cast degenerate, they form the coarse granules in the coarsely granular cast.
Earlier Theory of the Genesis of Casts:
Key:
A = Cellular casts
B = Coarsely granular cast
C = Finely granular cast
D = Waxy cast
Current Theory of Cast Genesis:
The most current theory of cast formation takes "C" finely granular
casts out of this sequence and gives it a genesis of its own. This
theory suggests that finely granular casts contain elements form
deteriorating renal tubular cells. These elements become trapped into
the protein matrix as it coagulates within the tubule.
White blood cell casts are formed when leukocytes enter the urine stream by amoeboid movement through and between the tubular epithelial cells or by passing from the glomerular capillary lumen across the basement membrane into the renal tubule lumen. The number of cells present in the cast may vary from a few to several. White blood cell casts are usually indicative of a renal inflammatory process such as pyelonephritis. The presence of white cell casts is usually accompanied by free and clumped white cells in the urine. If both white cell casts and red cell casts are present, the cells may be of glomerular origin as in diseases like glomerulonephritis.
This is a good example of a white cell cast. Note how easy it is to identify the individual cells within the matrix of the cast.
Red blood cell casts have an orange-red to brown hue from the presence of hemoglobin. The red cells may appear intact as biconcave discs embedded in the cast matrix, although frequently the red cells appear only as an outline because they have degenerated. When degeneration has occurred, the cast appears granular and can often be recognized by the hemoglobin pigmentation. The presence of red cell casts is usually accompanied by the presence of free red cells in the sediment also. When red blood cell casts are observed in the urine, the glomerular basement membrane or the epithelial lining of the renal tubule may be injured. Thus, red cell casts are frequently found in glomerulonephritis. Occasionally, red cell casts may be seen in an individual who has been playing contact sports. The urines of these individuals will return to normal within 24 to 48 hours.
This is a very long red cell cast that is hard to identify because you can't see the rounded ends. But it is easy to identify the cells within the cast matrix.
Epithelial cell casts consist predominantly of renal tubular epithelial cells. Although some of these cells are being shed and renewed continuously, their presence in casts indicates that a kidney lesion is present caused by any toxic or infective process. Typically, in an epithelial cast, the cells are arranged in more or less parallel rows. These casts are identified by the large size and prominent nucleus of the cells that are present. Renal tubular cell casts can often be accompanied by proteinuria and granular casts.
In general, coarsely granular casts are the result of degeneration of any of the cellular casts. Because of the fragmentation of nuclei and the disruption of cellular membranes, coarse granular particles are formed. These casts are usually accompanied by the cellular casts.
This is a very good example of a coarsely granular cast. You can see distinct granules within the matrix; some of the granules have almost retained the shape of the cells that preceded them. Also note the red cell and the mucus in this field.
Finely granular casts are believed to contain the by-products of protein metabolism that are excreted by the renal tubular epithelial cells. This is why finely granular casts may be found in the urine of normal individuals. Another theory for finely granular casts, especially when they are not accompanied by other casts, is that, as the renal tubular cells degenerate, they release their intracellular components into the tubular lumen which become enmeshed in the cast. The presence of these casts in normal individuals is not as common as hyaline casts; but may increase in the urine after strenuous exercise.
This frame is filled with casts and other elements. "A" points to a finely granular cast. Notice how much smaller the granules are compared to the cast you saw in the previous frame. In this frame, "B" points to a white cell cast. Note the numerous white cells, red cells and bacteria in this frame.
Waxy casts are the result of the coalescing of the protein in the matrix of the cast and further degeneration of the cellular elements entrapped in the cast. The protein becomes brittle and can crack and break easily. These casts have a high refractive index and blunt ends and appear colorless, yellowish or gray in color. They also have an opaque surface and serrated margins which often become creviced because they are so brittle. Waxy casts are found in patients with long standing chronic renal disease or chronic renal failure. Their presence implies tubular obstruction with prolonged stasis.
This frame shows an excellent example of a waxy cast. Note the blunt ends and the cracks or indentations in the cast. This cast also looks like it is filled with granules; but this may be an artifact from the preservation of the urine sediment.
Because of their wide width, broad casts are thought to be formed in dilated renal tubules. This can be indicative of urinary tract obstruction, decreased urine flow and severe chronic renal disease. These casts are often referred to as end stage or renal failure casts.
Ruthanne Hyduke, M.A.
Acid Urine pH |
Neutral Urine pH |
Alkaline Urine pH |
Ampicillin |
None |
None |
Bilirubin |
|
|
Cholesterol |
|
|
Cystine |
|
|
Leucine |
|
|
Radiographic contrast media |
|
|
Sulfonamides |
|
|
Tyrosine |
|
|
Ampicillin can appear in the urine of patients on high-dose antibiotic therapy. They look like long, thin needles or prisms and are colorless. Confirm these crystals by verifying the patient's therapy.
Bilirubin crystals are fine needles or granules that form clusters and are yellow-brown in color. They will be accompanied by positive chemical reaction for bilirubin on the reagent strip. Confirm these crystals by dissolving in strong acid and alkali.
The arrow in this frame is pointing to a cluster of bilirubin crystals.
Cholesterol crystals are flat, rectangular plates with notched corners and are colorless. They are found in lipiduria or with other forms of urinary fat. These crystals are confirmed by their solubility in chloroform and ether.
This cholesterol crystal gives the appearance of being a flat plate with a notched (missing) corner.
Cystine crystals are clear, colorless hexagonal plates often appearing in layers. They can be found in the amino acid disorder of cystinuria or cystinosis. These crystals are confirmed by their solubility in alkali.
This frame clearly shows the hexagonal shape of the cystine crystal. This particular crystal looks as though two large crystals precipitated overlapping each other with several other crystals lying on top of the two.
Leucine crystals are spheres with concentric circles or radial striations and appear dark yellow to brown in color. They may be present in severe liver disease and aminoacidurias. They often accompany tyrosine and are confirmed by their solubility in alkali.
Tyrosine appears as fine, delicate needles in clusters or sheaves. They can appear colorless to yellow. They are found in liver disease and aminoaciduria. Confirm these crystals by dissolving in alkali.
Note how fine these crystals appear. While the crystals in this frame are very easy to see, that is not always true. In fresh urine, they are very difficult to see and can be easily missed.
Radiographic contrast media can take two forms: long pointed needles or flat, elongated rectangular plates. They are colorless and must be confirmed by determining whether the patient has undergone any radiographic procedures.
This concludes the study of the different elements found in urine sediment. In Part IIB. you studied those elements that are seen in almost every urine and artifacts that are often confused with urine elements. Finally, in Part IIC you studied those elements that are clinically significant as they accompany a variety of different diseases. You are now ready to take Exam II which covers the urine microscopic examination.
Ruthanne Hyduke, M.A.
Davies J, Kargacin L, ed. Elaborations. Seattle WA. Washington State Department of Health, August 1996.
Package insert: Ames (tm) N-Multistix ® SG, Miles, Inc. Diagnostic Division, 1993.
Package insert: Chemistrips ®, Boehringer Mannheim Corporation, 1994.
Strasinger SK: Urinalysis and Body Fluids (2nd ed.), Philadelphia, PA, F.A. Davis Company, 1989.
Squamous
Epithelial Cells
Transitional
Epithelial Cells
Red
Blood Cells
White
Cells
Yeast
Bacteria
Trichomonas
Vaginalis
Casts
Normal
Urine Crystals
Mucus
Sperm
Artifacts
Abnormal
Crystals