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Fibrillarin (U3 RNP) Antibody, IgG
2012173
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.

Mnemonic
U3 FIB
Methodology
Qualitative Immunoblot
Performed
Tue, Thu, Sat
Reported
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
 
Collect
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. 
Remarks
 
Stability
After separation from cells: Ambient: 48 hours; Refrigerated: 2 weeks; Frozen: 1 year 
Reference Interval
Negative
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: 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.

Note
CPT Code(s)
86235
Components
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.
Aliases