Autoantibody Testing and Inflammatory Markers
Mariana Gonzalez Trevino
Initial Laboratory Panel
- CBC, BMP, HFP, UA, ESR/CRP, TSH (exclude thyroid disease as rheumatic mimic).
- Target serological testing based on clinical syndrome/suspicion (see below).
| Antibody | Associated Diseases | Interpretation/Monitoring Comments |
|---|---|---|
| ANA (Antinuclear Antibody) | SLE, Sjögren, SSc, MCTD, drug-induced lupus, autoimmune hepatitis; also positive in healthy individuals (up to 30%) | Screening test only. Titer ≥1:80 is significant. Do NOT repeat once positive. Does NOT correlate with disease activity. A high titer nucleolar ANA is concerning for scleroderma even if the reflex testing is negative. Myositis patients may have a negative ANA. |
| CONNECTIVE TISSUE DISEASES | ||
| Anti-dsDNA | SLE; lupus nephritis | Monitor serially in established SLE. Correlates with disease activity, especially lupus nephritis. Rising titers may predict flare. |
| Anti-Smith (Sm) | SLE | Baseline only. Highly specific for SLE. |
| Anti-U1 RNP | MCTD (defining antibody), SLE, overlap syndromes | Baseline only. High titer in isolation suggests MCTD. |
| Anti-Histone | Drug-induced lupus (DIL), Felty Syndrome | Baseline only. Common medications causing DIL: TNFi, procainamide, hydralazine, minocycline, phenytoin, lithium, INH, quinidine, terbinafine. |
| Anti-Ribosomal P | SLE; neuropsychiatric lupus (NPSLE), lupus hepatitis | Uncertain clinical utility. |
| Anti-C1q | SLE; lupus nephritis (especially proliferative) | May monitor in lupus nephritis. Correlates with renal disease activity. |
| Anti-SSA/Ro | Sjögren, SLE, PBC, ILD, neonatal lupus | Baseline. Repeat if newly pregnant or planning pregnancy in SLE, RA, and SSc. Predicts congenital heart block risk for the child in expecting mothers. |
| Anti-SSB/La | Sjögren, SLE, neonatal lupus | Baseline only. Combined Ro/La positivity in Sjögren is associated with lymphoma risk factors. |
| Anti-Centromere (ACA/CENP-B) | Limited cutaneous SSc (lcSSc), CREST, primary biliary cholangitis | Baseline only. Associated with PAH, digital ulcers, calcinosis. Lower ILD risk. |
| Anti-Scl-70 (Topoisomerase I/ATA) | Diffuse cutaneous SSc (dcSSc) | Baseline only. Associated with severe ILD, digital ulcers, diffuse skin involvement. Worse prognosis. |
| Anti-RNA Polymerase III (RNAP III) | Diffuse cutaneous SSc; malignancy | Baseline only. CANCER SCREENING REQUIRED. Associated with rapid skin progression and scleroderma renal crisis (SRC). |
| Antiphospholipid Antibodies (aCL IgG/IgM, anti-β2GPI IgG/IgM, LAC) | Antiphospholipid syndrome (APS), SLE (20–40% of patients) | Baseline, then repeat in 12 weeks to confirm persistence. Positive LAC or triple positivity indicates highest thrombosis risk. Check if thrombosis, recurrent pregnancy loss, or unexplained prolonged PTT. ALL SLE PATIENTS SHOULD BE SCREENED FOR aPL. Testing should be repeated with new pregnancy or pregnancy planning. |
| INFLAMMATORY ARTHRITIS | ||
| Rheumatoid Factor (RF) | RA, Sjögren, cryoglobulinemia, chronic infections (HCV, TB, endocarditis) | Baseline only. Less specific than anti-CCP for RA. High titers associated with extra-articular disease and worse prognosis. May be positive in any condition with chronic B-cell stimulation. |
| Anti-CCP (ACPA) | RA | Baseline only. Predicts erosive disease. Can precede clinical RA by years. |
| HLA-B27 | Ankylosing spondylitis, reactive arthritis, PsA, IBD-arthritis, uveitis | Baseline only. Supports SpA diagnosis but NOT diagnostic alone. Helpful for patients with uveitis. Sensitivity ~50%, specificity ~90% for AS. |
| ANCA-ASSOCIATED VASCULITIS | ||
| PR3-ANCA (c-ANCA) | Granulomatosis with polyangiitis (GPA) (85%); some MPA (15%) | Baseline for diagnosis. PR3+ patients have higher relapse rates than MPO+. Persistence may modestly predict relapse. |
| MPO-ANCA (p-ANCA) | Microscopic polyangiitis (MPA) (85%); EGPA (40%); some GPA (15%) | Baseline for diagnosis. Associated with more renal involvement. Lower relapse rate than PR3+. |
| MYOSITIS-SPECIFIC ANTIBODIES (MSAs) | ||
| Anti-Jo-1 (histidyl-tRNA synthetase) | Anti-synthetase syndrome (most common ASS antibody, 15–25% of IIM) | Baseline only. Associated with ILD, arthritis, mechanic’s hands, Raynaud’s, fever. |
| Anti-Mi-2 | Classic dermatomyositis | Baseline only. GOOD PROGNOSIS. Excellent response to steroids. Prominent skin manifestations (heliotrope rash, Gottron papules, shawl sign). Higher relapse risk but favorable survival. |
| Anti-MDA5 (CADM-140) | Clinically amyopathic DM (CADM) | Baseline only. HIGH MORTALITY RISK. Associated with rapidly progressive ILD (RP-ILD), skin ulcers, arthritis, alopecia. Requires aggressive ILD screening and early immunosuppression. |
| Anti-TIF1-γ (p155/140) | DM with malignancy (adults >40); juvenile DM | Baseline only. CANCER SCREENING REQUIRED. Strongest malignancy association (OR 3.5). |
| Anti-SRP (signal recognition particle) | Immune-mediated necrotizing myopathy (IMNM) | Baseline only. Severe, treatment-resistant myopathy; cardiac involvement. |
| Anti-HMGCR | IMNM | Baseline only. Statin-associated myopathy (but can occur without statin exposure). |
Key pearls for interpretation
- While ANA patterns (homogenous, speckled, nucleolar, centromere, cytoplasmic) can suggest specific antibodies, they are NOT diagnostic alone. Always reflex to specific antibody testing. At VUMC, ANA will automatically reflex to DNA/ENA panel if positive.
- Only anti-dsDNA, complement C3/C4, and anti-C1q correlate with disease activity and can be monitored serially in SLE. Most other antibodies are diagnostic markers only and do NOT change with disease activity—check at baseline and do not repeat.
- ANA can be positive in up to 30% of healthy individuals (especially elderly), chronic infections, malignancy, and with certain medications. Always interpret in clinical context. Low-titer ANA (<1:160) in asymptomatic patients often lacks clinical significance.
- For antiphospholipid antibodies (aPL), two positive tests at least 12 weeks apart are required for APS diagnosis. Do not diagnose APS on a single positive test, especially during acute illness when transient positivity can occur. For aCL and anti-β2GPI, titers > 40 units or >99th percentile are considered clinically significant. Need hematology approval to order aPL panel inpatient.
| Test | Clinical Utility | Interpretation Pearls |
|---|---|---|
| ACUTE PHASE REACTANTS | ||
| ESR | Nonspecific marker of inflammation. Reflects preceding 7-10 days. | Elevated in: PMR/GCA (≥40 mm/hr in classification criteria), RA, SLE, infections, malignancy, anemia, pregnancy. Affected by: immunoglobulins, RF, anemia (↑ESR), polycythemia (↓ESR), DIC (↓ESR), and MAS (↓ESR). |
| CRP | More specific acute phase reactant; faster response than ESR. Reflects preceding 24 hours. | Elevated in: Infection, RA, PMR/GCA, AOSD, serositis. SLE: Can be positive >50-60 mg/L. In SLE, elevated CRP suggests infection. In RA, CRP correlates better with inflammatory activity than ESR. |
| Ferritin | Key marker in hyperferritinemic syndromes: AOSD, HLH/MAS, catastrophic APS, sepsis. | AOSD: Markedly elevated (often >1000 ng/mL); ferritin >1225 ng/mL predicts AOSD. HLH: Often >10,000 ng/mL. Glycosylated ferritin ≤20% more specifically predicts RP-ILD. |
| Procalcitonin (PCT) | Helps distinguish bacterial infection from autoimmune flare. | Infection vs. flare: PCT ≥0.5 ng/mL strongly suggests bacterial infection. NOT elevated in uncomplicated autoimmune flares. Caution: May be elevated in severe systemic inflammation. |
| MUSCLE ENZYMES | ||
| CK | Most sensitive marker of muscle damage. | IMNM: Very high (often >50× ULN). PM/DM: Elevated but variable (may be 10× ULN). IBM: Often only mildly elevated or normal. Anti-MDA5 DM: Often NORMAL despite active disease. Normal CK in up to 20% of myositis. AST/ALT can also be elevated (muscle source, not necessarily liver disease). |
| Aldolase | Complementary to CK; may be elevated when CK is normal. | DM: May be the ONLY elevated enzyme (especially with fasciitis or perimysial pathology). Elevated aldolase + normal CK: Think DM, overlap myositis, fasciitis. |
| LDH | Nonspecific marker of tissue damage. | Myositis: Elevated with CK/aldolase. HLH: Often markedly elevated. Hemolysis: Elevated LDH with concomitant indirect hyperbilirubinemia and low haptoglobin. Malignancy: Lymphoma. Infection: PJP. |
| CRYSTAL DISEASE MARKERS | ||
| Uric Acid (Serum Urate) | Gout | During flare: May be NORMAL (inflammation increases renal excretion), so do NOT use to rule out gout. Diagnosis: Low specificity; most hyperuricemic patients never develop gout. Target <6 mg/dL on urate-lowering therapy. Approximately 95% of gout flares occur with urate ≥6 mg/dL. |
| COMPLEMENT | ||
| C3 | Consumed in immune complex diseases. | Low in: Active SLE (especially nephritis), cryoglobulinemia, MPGN, endocarditis. Normal/high in: RA, vasculitis (acute phase reactant). SLE: Low C3 + low C4 + elevated anti-dsDNA = active disease. |
| C4 | More sensitive than C3 for SLE activity; very low in cryoglobulinemia. | Very low C4: Think cryoglobulinemia (often <10 mg/dL), hereditary angioedema, active SLE. C4 often decreases before C3 during flare. Cryoglobulinemia: Disproportionately low C4 with near-normal C3. |
| OTHER | ||
| Soluble IL-2 Receptor | T-cell activation marker; HLH diagnosis. | HLH: Elevated (>2400 U/mL in HLH-2004 criteria). AOSD vs. HLH: >3900 U/mL favors AOSD; >3900 U/mL also favors HLH depending on clinical context. |
| Fibrinogen | Acute phase reactant; consumed in HLH/DIC. | HLH: Hypofibrinogenemia (<150 mg/dL) due to consumption. DIC: Low fibrinogen with elevated D-dimer. Inflammation: Elevated as acute phase reactant. |
| Triglycerides | Elevated in HLH. | HLH: Hypertriglyceridemia (≥265 mg/dL or ≥3 mmol/L) in HLH-2004 criteria. Mechanism: Lipoprotein lipase inhibition by cytokines. |
| D-dimer | Fibrinolysis marker; elevated in inflammation, thrombosis, DIC. | HLH: Often markedly elevated. AOSD vs. HLH: Similar levels in both (not discriminatory). COVID-19/MIS: Elevated in cytokine storm. |
| Cryoglobulins | Diagnose cryoglobulinemic vasculitis. |
Type I: Monoclonal Ig (IgM or IgG),
associated with lymphoproliferative disorders;
precipitates within hours. Type II/III (mixed): Polyclonal IgG + monoclonal/polyclonal IgM with RF activity; accounts for 85-90% of cases; HCV is the leading cause; may take days to precipitate. CRITICAL: Sample must be collected, transported, and processed at 37°C. Talk to laboratory staff regarding logistics before ordering. |