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HelpTest Code RNP RNP Antibodies, IgG, Serum
Reporting Name
RNP Ab, IgG, SUseful For
Evaluating patients with signs and symptoms of a connective tissue disease in whom the test for antinuclear antibodies is positive
Testing for ribonucleoprotein particle antibodies is not useful in patients without demonstrable antinuclear antibodies.
Testing Algorithm
For more information see Connective Tissue Disease Cascade.
Method Name
Multiplex Flow Immunoassay
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
SerumSpecimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
Specimen Minimum Volume
0.35 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 21 days | |
| Frozen | 21 days |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | OK |
Special Instructions
Reference Values
<1.0 U (negative)
≥1.0 U (positive)
Reference values apply to all ages.
Day(s) Performed
Monday through Saturday
CPT Code Information
86235
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| RNP | RNP Ab, IgG, S | 29958-6 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| RNP | RNP Ab, IgG, S | 29958-6 |
Clinical Information
Antibodies to U1 ribonucleoprotein particle (U1-RNP) are central to the diagnosis of mixed connective tissue disease and are also associated with other antinuclear antibody (ANA)-associated connective tissue diseases (CTDs) such as systemic lupus erythematosus, systemic sclerosis, undifferentiated CTD, and CTD overlap syndromes.(1-5) Immunologic characterization studies suggest that anti-U1RNP antibodies are directed toward both discontinuous and linear epitopes that are either contained in the protein sequence or are post-translationally modified. These antibodies mainly target the RNP68 or RNP70, RNPA (33 kD), and occasionally RNPC (22 kD) proteins.(4-9)
Originally described by Mattioli et al (3) by immunodiffusion assay using calf thymus extract, current solid-phase immunoassays now use diverse analytes (purified or recombinant proteins, synthetic peptides of dominant epitopes) of the 3 main proteins (RNP68 or RNP70, RNPA, and RNPC) either singly or in any of the various combinations.(4-10) Because of the use of these different antigens and combinations thereof, the nomenclature, reporting, and interpretation of anti-U1RNP antibodies remain obscure.(10) In the absence of standardized nomenclature for anti-U1-RNP antibody assays, familiarity of the analytes in specific assays and use of Hep-2 substrate by indirect immunofluorescence assay for ANA are required for appropriate interpretation. In addition, low level anti-U1-RNP antibodies in the absence of ANA have a low predictive value for ANA-CTD. The U1-RNP antibody test offered by Mayo Clinic detects antibodies to both RNP68 and RNPA proteins. Combined response is more sensitive and less specific than assays to the Sm (Smith)/RNP.(10)
For more information see Connective Tissue Disease Cascade.
Interpretation
A positive result for anti-ribonucleoprotein particle 68/A (RNP68/A) antibodies in association with positivity of antinuclear antibodies may be consistent with a diagnosis of connective tissue disease.
Cautions
The U1 ribonucleoprotein particle (RNP) 68/A antibody is more sensitive than the Sm (Smith)/RNP antibody test. Low positive results (≤4.0 U) without an associated positive antinuclear antibodies by indirect immunofluorescence assay should be interpreted with caution.
Method Description
Recombinant ribonucleoprotein particle (RNP)-68 and RNP-A antigens are bound to polystyrene microspheres, which are impregnated with fluorescent dyes to create a unique fluorescent signature. RNP antibodies, if present in diluted serum, bind to the RNP antigens on the microspheres. The microspheres are washed to remove extraneous serum proteins. Phycoerythrin (PE)-conjugated antihuman IgG antibody is then added to detect IgG anti-RNP bound to the microspheres. The microspheres are washed to remove unbound conjugate, and bound conjugate is detected by laser photometry. A primary laser reveals the fluorescent signature of each microsphere to distinguish it from microspheres that are labeled with other antigens, and a secondary laser reveals the level of PE fluorescence associated with each microsphere. Results are calculated by comparing the median fluorescence response for RNP microspheres to a 4-point calibration curve.(Package insert: Bioplex 2200 ANA Screen. Bio-Rad Laboratories; 02/2019)