Fibrillarin (U3 RNP) Antibody, IgG
Ordering Recommendation

Recommended for the diagnosis of systemic sclerosis in patients negative for centromere, Scl-70, or RNA polymerase III antibodies. May predict skeletal muscle involvement and pulmonary arterial hypertension.

Qualitative Immunoblot
Tue, Thu, Sat
1-4 days
New York DOH Approval Status
This test is New York DOH approved.
Submit With Order
ARUP Consult®
Disease Topics
Specimen Required
Patient Preparation
Serum separator tube. 
Specimen Preparation
Transfer 1 mL serum to an ARUP Standard Transport Tube. (Min: 0.5 mL) 
Storage/Transport Temperature
Refrigerated. Also acceptable: Frozen. 
Unacceptable Conditions
Grossly hemolyzed or severely lipemic. 
After separation from cells: Ambient: 48 hours; Refrigerated: 2 weeks; Frozen: 1 year 
Reference Interval
Interpretive Data
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 percent with the gold standard immunoprecipitation (IP) assay. Approximately 71 percent (5/7) of the borderline U3-RNP results with ANA nucleolar pattern in this cohort were IP negative.

Compliance Statement D: For laboratory tests using a manufactured RUO kit. This test was developed and its performance characteristics determined by ARUP Laboratories. The U. S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.

Hotline History
Component Test Code*Component Chart NameLOINC
2012174Fibrillarin (U3 RNP) Ab, IgG49963-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.