Dr. Julie Mongeau on the Laboratory Workup of Early SLE

Ordering an ANA “just to rule out lupus” is one of the most common — and most consequential — testing decisions in primary care. In Part 2 of Virtual Hallway’s early SLE diagnosis series, Dalhousie-trained rheumatologist Dr. Julie Mongeau delivered a masterclass on rheumatologic investigations: what routine blood work can tell you, how to interpret inflammatory markers, and why the ANA is so frequently misused. Here are the essential takeaways from her expert session and why you should catch the full recording.

Start with Routine Blood Work

Lupus is called the disease of a thousand faces, but the initial workup starts with tests you order every day. On the CBC, look for:

• Leukopenia (<4,000/µL), usually lymphopenia, though neutropenia occurs.
• Thrombocytopenia (<100,000/µL) — more specific for lupus, whereas marked thrombocytosis points elsewhere, especially infection.
• Anemia, typically from autoimmune hemolysis or chronic disease. For suspected hemolysis, check reticulocytes, haptoglobin, indirect bilirubin, LDH, direct Coombs, and the smear for spherocytes.

For the kidney — the organ complication rheumatologists worry about most — check creatinine, urinalysis for hematuria and proteinuria (and remember to consider menstruation before acting on hematuria), and quantify proteinuria, with more than half a gram per 24 hours being concerning. And a pearl for the liver panel: hepatitis is rarely due to lupus itself, so unexplained AST/ALT elevations with a negative liver workup should prompt a CK to look for myositis.

ESR vs. CRP: Choosing and Interpreting Wisely

Dr. Mongeau demystified the inflammatory markers:

• ESR is the older, less specific test — raised by age, female sex, anemia, obesity, pregnancy, diabetes, and renal disease. For older patients, the age-adjusted upper limit is age ÷ 2 for men and (age + 10) ÷ 2 for women.
• CRP is more dynamic, shifting within hours of a change in inflammatory state, making it the better monitoring tool.
• In lupus, expect only mild to moderate elevations. A CRP above 100 should make you think infection first — even in an established lupus patient — with serositis and vasculitis as the two lupus manifestations that can drive CRP that high.
• Know your local assay: high-sensitivity CRP flags results above 3 for cardiovascular risk purposes, which frequently triggers unnecessary rheumatology referrals for “elevated” CRPs of 6 or 9.

The ANA: Powerful, Misunderstood, and Massively Overused

The heart of the session. Virtually all lupus patients (99–100%) are ANA positive, so a negative ANA largely rules lupus out — but a positive one comes with a false positive rate of 5–30% in the general population. The numbers on overuse are striking: an Alberta review found roughly 60,000 ANA tests ordered per year against an expected ~200 new lupus cases, and a US rheumatology study found 17% of consults were for a positive ANA, with 81% of those patients having no rheumatic disease at all.

Other key points:

• Method matters. Indirect immunofluorescence is the sensitive gold standard; multiplex bead assays and ELISA test only a fixed antibody panel. In some labs, ordering an “ANA” actually orders a connective tissue disease panel — which will not answer a question about autoimmune liver disease.
• Don’t repeat a positive ANA. In one follow-up study, the ANA remained positive in 91% of patients a decade later, and only a small minority (under 6%) ever developed an ANA-associated rheumatic disease. Retest only if the clinical picture changes.
• Follow Choosing Wisely Canada: don’t order the ANA as a screen without specific signs or symptoms of lupus or another connective tissue disease. The downstream costs — inflated referral volumes, year-long waits, and patients left anxious and mislabeled — are the real price of the test.

Beyond the ANA: RF, Complements, and Antiphospholipid Antibodies

• Rheumatoid factor is not synonymous with rheumatoid arthritis (sensitivity 60–80%, specificity 80–90%). Dr. Mongeau’s CHRONIC acronym covers the differential: CHronic disease (hepatic, pulmonary), Rheumatoid arthritis, Other rheumatic diseases, Neoplasm, Infection (hepatitis B/C, endocarditis), and Cryoglobulinemia. Mild elevations in patients over 70 are often not clinically meaningful.
• Anti-CCP is highly specific for rheumatoid arthritis — a positive result should raise real suspicion.
• Complements (C3/C4): high levels just mean inflammation; low levels are the useful finding, suggesting consumption from an immune-complex process like lupus, cryoglobulinemia, or vasculitis. A normal result doesn’t rule out active lupus.
• Antiphospholipid antibodies (anticardiolipin, anti-beta-2 glycoprotein 1, lupus anticoagulant) are worth testing after unexplained thrombosis or obstetrical complications, with positivity confirmed 12 weeks apart.

The Takeaway

Blood tests are only one facet of rheumatologic diagnosis, with both false positives and false negatives. A good history and physical exam is more valuable than any serology — order the ANA when clinical suspicion warrants it, and refer when clinical concern persists even with negative tests, because patients can still have rheumatic disease with negative serologies.

Watch the Full Lecture

Ready to bring more precision to your rheumatologic workups? Watch the full session with Dr. Mongeau on Virtual Hallway to:

• Review her CRP interpretation table and full testing summary slides.
• Earn MainPro+ credits.
• Sign up for free at virtualhallway.ca

And if a puzzling ANA lands on your desk, remember you can book a direct consult with a rheumatologist in your province through Virtual Hallway. Log in, learn, and test wisely.