U3RNP Fibrillarin Ab




Test Mnemonic

U3RNP

CPT Codes

  • 86235 - QTY (1)

Aliases

  • Fibrillarin Ab

Includes

  • Fibrillarin (U3 RNP) Ab, IgG

Performing Laboratory

ARUP


Specimen Requirements

Volume Type Container Collect Temperature Transport Temperature Special Instructions
1 mLSerumSST (Gold) RefrigeratedTransfer 1 mL serum into standard aliquot tube.

Minimum Specimen Requirements

Volume Type Container Collect Temperature Transport Temperature Special Instructions
0.5 mL     

Stability

Environmental Condition Description
AmbientAfter separation from cells: 48 hours
RefrigeratedAfter separation from cells: 2 weeks
FrozenAfter separation from cells: 1 month (avoid repeated freeze/thaw cycles)

Days Performed

Tue, Thu, Sat

Turnaround Time

2 - 5 days

Methodology

Name Description
Immunoblot (IB), Qualitative 

Reference Range

Special Info

Grossly hemolyzed or severely lipemic specimens will be rejected. This test is New York DOH approved.

Clinical Info

This test is recommended for the diagnosis of systemic sclerosis in patients negative for centromere, Scl-70, or RNA polymerase III antibodies. It may predict skeletal muscle involvement and pulmonary arterial hypertension. The presence of fibrillarin (U3-RNP) IgG antibodies in association with an ANA IFA nucleolar pattern is suggestive of systemic sclerosis (SSc). In SSc, these antibodies are associated with distinct clinical features, such as younger age at disease onset, frequent internal organ involvement (pulmonary hypertension, myositis and renal disease). Fibrillarin antibodies are detected more frequently in African American patients with SSc compared to other ethnic groups. Strong correlation with ANA IFA results is recommended. In a multi-ethnic cohort of SSc patients (n=98), U3-RNP antibodies detected by immunoblot had an agreement of 98.9% with the gold standard immunoprecipitation (IP) assay. Approximately 71% (5/7) of the borderline U3-RNP results with ANA nucleolar pattern in this cohort were IP negative.