Rheumatology Serology Overview

Suspecting Lupus: patients with arthritis, malar rash, Raynaud’s, alopecia, serositis

⇨ Screen with: ESR, CRP, & ANA ➙ if +

⇨ Refer to rheum, or ⇨ Anti ds-DNA, ENA & C3/C4, then refer to rheum:
⇨ if negative ➙ very unlikely to be systemic lupus erythematosus (SLE), especially if ENA is negative
⇨ if positive ➙ refer to rheum to assess for Lupus or other connective tissue disease (CTD) ⍟ ANA is Sn, but not Sp ➙ 20-30% of normal can have it positive

Suspecting Rheumatoid Arthritis (RA): patients with small/large joint inflammatory arthritis

⇨ Screen with: ESR, CRP, RF ➙ if +

⇨ Anti-CCP
⍟ Not covered in the community
⍟ Cost is ≥ $100
⍟ Can be negative early in the disease
⍟ If >2-3 folds of the UL of N ➙ 50% will get RA in the next 5 years

Suspecting SLE or RA:

⇨ Screen with: ESR, CRP, ANA & RF ➙ if +

⇨ Refer to rheum, or
⇨ Anti ds-DNA, ENA & C3/C4, Anti-CCP, then refer to rheum:

⍟ Once a patient is ANA, RF, or Anti-CCP Positive ➙ NO need to repeat it ⍟
They are not useful in measuring disease activity

Suspecting inflammatory back pain ≈ Ankylosing Spondylitis

⇨ Screen with dedicated SI x-rays (not just LS spine x-ray) ⇌ + ⇌ HLA B27

⇨ If x-ray is negative, but history suggestive ➙ MRI
⍟ Don’t order ANA ➙ SLE doesn’t come with back pain

Authors: Dr. Ahmed Aljefri MD CFP and Dr. Natasha Gakhal MD FRCP (May 12, 2021 PR ND)

Abbreviations:

ANA – anti-nuclear antibody

Anti CCP – anti- cyclic citrullinated peptides

Anti ds-DNA –  anti – double stranded DNA

C3 – Complement component 3

C4 – Complement component

CRP – C-reactive protein

CTD – Connective tissue disease

ENA – Extractable nuclear antigen panel

ESR – erythrocyte sedimentation rate

HLA-B27 – human leukocyte antigen B27

RF – Rheumatoid factor

References:

Featured image – Wasserman AM. Diagnosis and management of rheumatoid arthritis. Am Fam Physician. 2011 Dec 1;84(11):1245-52. PMID: 22150658.