Recent polyarthritis or oligoarthritis in adults (early inflammatory arthritis, before diagnosing RA)

• Fever, chills, infectious portal of entry or organ involvement: opinion or emergency department without waiting for the tests.

Laboratory tests

• FBC
• CRP
• Rheumatoid factor
• Anti-CCP antibodies
• Antinuclear antibodies (stating the clinical context)
• Serum creatinine with eGFR
• AST
• ALT
• Anti-dsDNA antibodiesif neededPositive antinuclear antibodies lead to testing for anti-DNA and anti-ENA ^[1]; in a global prescription, the NABM reimburses them only if the antinuclear antibodies are positive ^[2].
• Anti-ENA antibodiesif neededPositive antinuclear antibodies lead to testing for anti-DNA and anti-ENA ^[1]; in a global prescription, the NABM reimburses them only if the antinuclear antibodies are positive ^[2].
• Serum urate (if foot or ankle involvement or previous attacks suggesting gout)if neededA serum urate > 360 µmol/L points to gout, but hyperuricaemia may be asymptomatic and serum urate may be normal during the attack ^[3].
• Hepatitis B serologyif neededJaundice or liver abnormalities point to viral hepatitis B or C in oligoarthritis or polyarthritis ^[3]; raised transaminases point to viral or autoimmune hepatitis ^[1].
• Hepatitis C serologyif neededJaundice or liver abnormalities point to viral hepatitis B or C in oligoarthritis or polyarthritis ^[3]; raised transaminases point to viral or autoimmune hepatitis ^[1].
• Parvovirus B19 serology, IgG and IgM (if rash or contact with young children)if neededA viral erythema (parvovirus, rubella) is among the guiding signs of oligoarthritis or polyarthritis ^[3]; NABM procedure 1763 covers the diagnosis of recent infection (IgG and IgM) ^[2].
• Lyme serology (if tick bite in an endemic area or history of erythema migrans)if needednon-French guidelineThe American College of Rheumatology (Choosing Wisely campaign), taken up by American Family Physician in 2023, says to look for Lyme disease in joint symptoms only in case of exposure and suggestive clinical signs ^[4]. The COFER lists a history of erythema migrans among the guiding signs of oligoarthritis or polyarthritis ^[3]. See the page “Lyme borreliosis: tick bite, erythema migrans, disseminated forms”.
• Chlamydia trachomatis and gonococcus NAAT (PCR) on first-void urine (if urethritis, at-risk intercourse, lower-limb oligoarthritis)if neededUrethritis and infectious diarrhoea point to reactive arthritis, urethritis and risk behaviour to gonococcal infection ^[3]; the NABM lists the aetiological diagnosis of reactive arthritis among the indications for this PCR ^[2].
• Joint fluid examination: cytology, bacteriology, crystals (if effusion in a joint that can be aspirated)if neededAspiration remains routine for an unexplained effusion, even in oligoarticular or polyarticular involvement ^[3]; it is done whenever possible on a medium or large joint ^[1].

Urine tests

• Urine dipstick (proteinuria, haematuria)