Specimen

Serum

Collection Medium:

Minimum:

Adult - 5 ml; red top tube
Pediatric - 2 ml; red top tube

Testing Schedule:

Testing performed once a week.

Analytic Time:

1 week

Reference Range:

Negative = < 20 units
Weak positive = 20-39 units
Moderate positive = 40-80 units
Strong positive = > 80 units

Comments:

When indirect immunofluorescence test for ANA is positive, the tests 
for anti-Sm and anti-RNP are helpful in differential diagnoses of 
various rheumatic diseases.  The specificity of the anti-RNP detected 
is for U-1-RNP (U1-RNP).

These two tests are most informative when ordered together in the 
initial evaluation of patients for autoimmune connective tissue 
diseases.  Anti-Sm is a specific marker antibody for systemic lupus 
erythematosus (SLE) but is positive in only about one-third of cases. 
Anti-RNP will also be positive whenever anti-Sm is detected, but
can be detected in some SLE patients in the absence of anti-Sm.  
Anti-RNP may also be found in several other autoimmune connective 
tissue diseases, however. It is particularly associated with mixed 
connective tissue disease in which very high levels of anti-RNP are 
present.

The tests are listed together as "anti-RNP/SM" on the current 
Immunopathology Laboratory requisition (Form A-1a).  If this box is 
checked, then both EIA assays will be performed and two charges will be 
generated.

Methodology:

Enzyme Linked Immunosorbent Assay (ELISA)