Top 10 Labs in Rheumatology — And How to Interpret Them

Ordering is easy.
Interpreting in context is where clinical medicine begins 👇
#Rheumatology #MedTwitter
@IhabFathiSulima @DrAkhilX

1/
🔬 ANA (Antinuclear Antibody)
✅ Best screening test for CTDs
🧠 Significant = ≥1:160
⚠️ False positives common (up to 15% in healthy adults)
🔍 Pattern helps:
•Homogeneous → SLE
•Speckled → Sjögren’s, MCTD
•Centromere → Limited SSc
•Nucleolar → Diffuse SSc

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2/
🔬 Anti-dsDNA
🎯 Highly specific for SLE
📈 Levels correlate with disease activity
⬆️ Rising titres suggest flare, especially nephritis

3/
🔬 Anti-Sm (Smith)
✅ Highly specific for SLE
❌ Not sensitive (~25%)
🧠 Once positive, always positive
🚫 Does not track disease activity

4/
🔬 Anti-Ro/SSA & Anti-La/SSB
🎯 Sjögren’s, SLE, subacute cutaneous lupus, neonatal lupus
⚠️ Anti-Ro + pregnancy → risk of congenital heart block
📌 Ro+ can occur even if ANA-negative

5/
🔬 Rheumatoid Factor (RF)
📌 IgM against IgG Fc
⚠️ Non-specific: ↑ in infections, liver disease, age
🧠 High titers = worse prognosis in RA
🎯 Confirm with anti-CCP

6/
🔬 Anti-CCP (ACPA)
✅ High specificity (~95%) for RA
📌 Appears early, even pre-clinical
📈 Predicts erosive, severe disease
🧠 Stronger diagnostic tool than RF

7/
🔬 ANCA (c-ANCA/p-ANCA)
🎯 Used for vasculitis work-up
•c-ANCA (PR3) = GPA
•p-ANCA (MPO) = MPA, EGPA
⚠️ Always confirm with ELISA
📌 False + in infections, IBD, drugs

8/
🔬 Complement (C3/C4)
⬇️ Low in active lupus, especially nephritis
📈 Rising = improvement
🎯 Also low in cryoglobulinemia, immune complex vasculitis

9/
🔬 Ferritin
📈 Acute phase reactant
🎯 Very high (>10,000) in MAS, AOSD
🧠 Mild elevation = inflammation
⚠️ Check with LDH, TG, AST in HLH work-up

10/
🔬 ESR & CRP
📌 CRP: rises/falls rapidly
📌 ESR: lags behind
🧠 CRP often normal in active SLE
📈 High CRP? Think infection or vasculitis

💡 Takeaway:
Lab values are tools, not answers.
Rheumatology = clinical reasoning + serology + follow-up