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Anti-U3 RNP Antibodies (Fibrillarin) (RDL)

CPT: 86235


  • Anti-Fibrillarin Ab
  • Anti-U3 RNP Ab
  • U3 RNP

Expected Turnaround Time

7 - 14 days

Specimen Requirements




1 mL

Minimum Volume

0.3 mL (Note: This volume does not allow for repeat testing.)


Red-top tube or gel-barrier tube


Separate serum from cells within one hour of collection. Transfer to a plastic transport tube before shipping. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

Storage Instructions

Refrigerate or freeze.

Stability Requirements



Room temperature

7 days


14 days


60 days

Freeze/thaw cycles

Stable x1

Causes for Rejection

Grossly hemolyzed; bacterial contamination; lipemic specimen; icteric specimen; non-serum specimen types

Test Details


The U3-RNP (Fibrillarin) particle is thought to participate in the first step of preribosomal RNA processing. Anti-U3 RNP antibodies have been shown to be highly specific for patients with SSc.


This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.


RIPA Gel Radiography

Additional Information

Anti-Fibrillarin (U3 RNP) antibodies are highly specific for diffuse SSc with a sensitivity of 4-10%. They are associated with isolated pulmonary arterial hypertension, myositis, renal and cardiac manifestations of SSc. 15% of IIM, mostly found in scleroderma/myositis overlap. Found in 4-10% of Diffuse SSc, <2% in Limited SSc, associated with isolated PAH, myositis, cardiac and renal involvement. More prevalent in African-Americans.

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