Specimen

Plasma

Collection Medium:

Minimum:

Full draw, any size blue top (mix well)  must be at least 90% full.

Delivery Instructions:

Deliver to laboratory immediately after collection.

Testing Schedule:

0800-1630 Monday through Friday.  For additional services, 
contact Clinical Pathology Resident on-call at pager #3404.

Analytic Time:

2 hours (upon receipt in laboratory)

Reference Range:

23-30 seconds

Critical value: 50 seconds (on outpatients only)

Comments:

Must be drawn swiftly with a clean venipuncture  (no hematoma).  Time 
drawn must be indicated on requisition.  Obtain special tube from lab 
if patient's hematocrit is over 55%.  If patient is on heparin therapy, 
samples must be in the lab within one hour after draw.  All other 
samples must be tested within four hours.

Activated Partial Thromboplastin time (aPTT) may be performed on the 
same collection tube as Prothrombin Time and Fibrinogen.

The laboratory changed to a new lot of PTT reagent on 2/10/07.  The 
mean of the reference range with this new reagent is 26 seconds; the 
reference range will be 23-30 seconds.  Because of the significant 
variability in response of the aPTT reagent systems to heparin, 40 
patient specimens with heparin levels of 0.3-0.7 U/ml were evaluated by 
an Anti-factor Xa method.  The mean of this group of specimens is 60 
seconds.  The aPTT values range from 38-96 seconds.  The mean of the 
published therapeutic range for heparinization of 1.5-2.5 times the 
mean of the reference range (26) yields values of 39-65 seconds with 
this reagent.  Based on our studies of heparin responsiveness, this is 
a reasonable target range to use with this reagent when treating 
uncomplicated venous thromboembolism.  Regarding the monitoring of 
heparin therapy this reagent represents only a slight change from our 
previous lot of aPTT reagent.

Methodology:

Optical clot detection.

CPT Code:

85730

See also:
Prothrombin Time, Plasma

See Additional Information:
Hematology Critical Lab Values
Heparin Therapy
Phlebotomy Tubes and Order of Draw
Specimens Requiring Immediate Delivery