04. Approach to Rheumatology Labs

Resident Editor: Megan Lockwood, M.D.

Faculty Editor: Jonathan Graf, M.D.


✔ Rheumatologic lab testing is of little value in patients in whom there is a low pre-test likelihood for a specific autoimmune condition

✔ ESR and CRP have limited diagnostic utility but may be useful in tracking disease activity in some autoimmune or infectious conditions

✔ A negative ANA by immunofluorescence essentially rules out SLE

✔ DNOT test for ANA sub-serologies without a positive ANA and clinical suspicion of an immune-mediated disease


  • Basic approach prior tordering any rheumatologic lab:
    • What autoimmune condition are you testing for?
    • What is the pre-test probability of the patient having the disease your testing for?
    • What are the limitations of the test you are ordering?


Nonspecific Inflammatory Markers

  • Erythrocyte Sedimentation Rate (ESR)
    • Measures the distance fallen by erythrocytes in a test tube over one hour
      • Elevated fibrinogen likely causes RBCs tsediment at a faster rate
    • A nonspecific, indirect marker of inflammation that can be elevated in infectious, autoimmune, or neoplastic conditions
      • Causes of elevated ESR (think causes of elevated fibrinogen/RBC’s): anemia, hypoalbuminemia, ESRD, DM, pregnancy, any state with presence of acute phase reactants
      • Causes of decreased ESR (think diminished fibrinogen/RBC’s): polycythemia, CHF, cryoglobulinemia, hypofibrinogenemia
    • Does not have specific diagnostic utility for rheumatic diseases, with the exception of polymyalgia rheumatica and giant cell arteritis
    • Some clinical utility in monitoring disease activity or response ttherapy in rheumatoid arthritis, temporal arteritis, and osteomyelitis
    • ESR rises with age:
      • Tcalculate the upper limit of normal: ESR ≤ age/2 (+5 in women)
  • C-reactive protein (CRP)
    • An acute phase reactant produced in the liver
    • More dynamic than ESR and tracks inflammatory event more closely in time
      • Increases in 4-6 hrs and normalizes within 1 week
    • Causes of elevated CRP: inflammatory conditions, obesity (adipose tissue makes iL-6 which can elevate CRP but rarely over 10 mg/L)
    • Not affected by anemia, gender, pregnancy, renal failure, (unlike ESR)
  • Complements
    • Classic complement cascade is activated by immune complexes
      • Integrity of entire classical cascade measured with CH50 functional assay
      • C3/C4 are most commonly measured individual components of pathway
    • Decreased level with increased complex-medicated activity (SLE, cryoglobulinemia)
    • Increased levels with other inflammatory disorders as they are acute phase reactants
    • C4>>C3 may indicate cryoglobulins
    • Other causes of low complements: endocarditis, post-strep glomerulonephritis and inherited deficiencies



  • Anti-Nuclear Antibody (ANA) – most commonly and accurately tested by indirect immunofluorescence
    • Auto-antibodies directed against intra-nuclear antigens (the test is NOT for the specific antigen, just detects the presence of these antibodies)
      • Positive ANA: can then use more specific testing (the “sub-serologies”) tlook for the specific antigen
        • Testing the sub-serologies can help tnarrow the diagnosis and determine the clinical significance of the positive ANA
          • Examples: anti-dsDNA, anti-histone, anti-Smith, anti-RNP, anti-SSA, anti-SSB, anti-RNP, anti-centromere, SCL-70
        • Once positive, ANA does not need tbe rechecked; fluctuating titers have nclinical significance
        • Titers ≥ 1:160: more likely trepresent true-positive results
        • Titers ≤ 1:40: less specific and less likely trepresent true rheumatologic diseases
        • Staining pattern has clinical significance (gives a clue as twhich molecules are being recognized by the antibodies): nuclear, cell cycle-associated, cytoplasmic
      • Negative ANA: generally nindication ttest for other antibodies
        • Exception: test for anti-SSA which on older assays for ANA could be missed. Test when there is high suspicion for Sjögren’s Syndrome or other disease accociated with SSA positivity.
    • Significance:
      • Nearly 100% sensitive for SLE (but remember, only one part of the criteria for SLE)
      • 30% of healthy people have positive ANA (highly non-specific, see below)
    • Common non-lupus related causes of a positive ANA:
      • Demographics: elderly, pregnant women, family history of SLE
      • Drug-induced:hydralazine, procainamide, quinidine, isoniazid, minocycline (homogeneous pattern reflects antibodies thistones)
        • Absence of anti-histone antibodies effectively rules out the disease (very high sensitivity, low specificity)
      • Other rheumatologic diseases: RA, scleroderma, Sjögren’s, MCTD, polymyositis, derematomyositis
      • Other autoimmune diseases: autoimmune thyroiditis, type 1 DM, pulmonary fibrosis, multiple sclerosis
      • Non-autoimmune diseases: HIV and other viral infections, liver disease, malignancy, endocarditis
  • Anti-RNP (ANA sub-serology)
    • 100% sensitivity for mixed-connective tissue disease (diagnostic criterion)
    • Alscommon in SLE
  • Anti-SSA (Ro) and Anti-SSB (La) (ANA sub-serology)
    • High sensitivity for primary Sjögren’ssyndrome
    • Dual antibody patients more likely thave sjogren’s syndrome with more severe and extra-glandular disease
    • Much lower percentage of positive antibodies in secondary Sjogren’s syndrome
    • Can alssee in SLE, especially with cutaneous involvement, and neonatal lupus
  • Anti-centromere (ANA sub-serology)
    • Classically associated with limited scleroderma (lcSSc) “CREST” syndrome
  • Rheumatoid Factor (RF)
    • An IgM (less commonly IgG and IgA) antibody directed against the Fc portion of self-IgG.
    • 80% sensitive for RA. Less specific for RA:
      • Commonly positive in many other conditions (see below)
      • All RF-positive arthritis is not RA!
    • Up t40% of RA patients may be RF negative early in their disease course, but many seroconvert over time.
    • Rf positivity correlates with disease severity (erosive disease) and extra-articular manifestations of RA
      • Once positive, serial RF titers are not useful for following disease progression
    • Common causes of a positive RF other than RA:
      • Demographics: elderly
      • Other autoimmune diseases: Sjogren’s, cryoglobulinemia, SLE, systemic sclerosis, mixed connective tissue disease
      • Non-autoimmune diseases: Chronic infections (HCV, endocarditis, osteomyelitis, tuberculosis, HIV), liver disease, sarcoidosis, multiple myeloma, MGUS.
  • Anti-citrullinated peptide (anti-CCP)
    • Antibodies against proteins containing citrulline, an aminacid created via a post-translational modification of arginine and
    • The immune response tcitrullinated proteins is thought tbe key tthe pathogenesis of RA
      • Newer generation of tests with similar sensitivity (80%) and improved specificity (95%) for RA compared tRF (should be ordered simultaneously in the appropriate clinical setting)
      • Can be detected years before onset of clinical disease
      • Associated with more aggressive and erosive disease
  • Cryoglobulins
    • Immunoglobulins that reversibly precipitate at cold temperatures
      • Precipitation can lead tvasculitis (as they often bind with proteins and form immune complexes)
    • Types of cryoglobulins (Brouet classification):
      • Type I: monoclonal Ig (often IgM or IgG isotypes)
        • Usually result from monoclonal expansion of malignant clone
          • Malignant: multiple myeloma, Waldenström’s, lymphoma
          • Indolent: MGUS
          • Secondary tlymphoproliferative disorder: CLL
      • Type II: monoclonal Ig + polyclonal Ig (mixed)
        • RF activity of monoclonal cryoglobulin à binding of polyclonal IgG tFc
          • Immune complex formation: Activates complement, associated with small and medium-sized vessel vasculitis
        • Often secondary tchronic infections: HBV, HCV, bacterial, parasitic
        • Seen in other autoimmune conditions: Sjögren’s, SLE, RA
      • Types III: polyclonal Ig (mixed)
        • RF activity of polyclonal cryoglobulin à binding of polyclonal IgG tFc
          • Immune complex formation: Activates complement, associated with small and medium-sized vessel vasculitis
        • As Often secondary tchronic infections: HBV, HCV, bacterial, parasitic
        • Seen in other autoimmune conditions: Sjogren’s, SLE, RA
      • Anti-neutrophil cytoplasmic antibody (ANCA)
        • Antibodies against cytoplasmic granules of neutrophils
          • Similar tANA, except against neutrophil-specific antigen
        • Immunofluorescence patterns:
          • C-ANCA
            • Correlates with serine protease-3 (PR-3) cytoplasmic protein
            • Associated with GPA (>90% sensitivity, specificity)
          • P-ANCA
            • Correlates with myeloperoxidase (MPO) peri-nuclear protein
            • Associated with MPA, EGPA, renal-limited vasculitis
          • Atypical p-ANCA pattern
            • May be seen in other autoimmune diseases with or without vasculitis (i.e. IBD, PSC, autoimmune hepatitis, connective tissue diseases)
            • Alsseen in drug-induced forms of vasculitis
        • Extreme caution with interpretation:
            • IF results must be confirmed by ELISAs for PR-3 and MPO
            • Pre-test probability is key when testing for rare diseases such as vasculitis, and positive tests should be interpreted with caution by experts
            • Titers may normalize with treatment and when disease is quiescent (beware the false negative in the setting of high pre-test probability!)
        • High titer atypical P-ANCA positivity associated with Levamisole-induced vasculopathy/vasculitis



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Kolopp-Sarda MN, Miossec P. Cryoglobulins: An update on detection, mechanisms and clinical contribution. Autoimmun Rev. Epub ahead of print: 2018 Mar 8.

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Graf J. Interpreting Rheumatologic Lab Tests. 41st Annual Advances in Internal Medicine in San Francisco, CA, May 2013. Oral Presentation.