Change in Test Methodology for Anti-RNP (Ribonucleoprotein)
and Anti-Sm (Smith) Antibodies

The Immunopathology Laboratory is changing the test methodology for anti-RNP and anti–Sm testing from hemagglutination to enzyme immunoassay (EIA) as of May 28, 2004.  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 new reference range for each of these tests is as follows:

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

The tests are listed together as “anti-RNP/SM” on the current Immunopathology Laboratory requisition (green and white, Form O-8).  If this box is checked, then both EIA assays will be performed and two charges will be generated. If only a single test is desired, please write the name of the test in under “other”.

The specimen type and volume needed are unchanged: Peripheral blood, one red-top tube (5 ml).

Turn-around time: Testing will be performed routinely on Friday mornings. The specimens must be received in the Immunopathology Laboratory by 9:00 AM to be included in the test run.

Please direct questions or comments to James Goeken, MD (356-1966); Michael Icardi, MD (339-7125), John Kemp, MD (384-9611) or Lisa Horning, MT, SI (ASCP) (356-2688).