Treatment: methotrexate (low weekly dose)

Laboratory tests

• FBC with platelets
• Serum creatinine with eGFR
• AST
• ALT
• Bilirubin
• Serum albumin
• Hepatitis B serology (HBsAg, anti-HBs, anti-HBc)
• Hepatitis C serology
• HIV serology (with the patient's consent)
• Serum β-hCG (if woman of childbearing potential)if neededMethotrexate is teratogenic: absence of pregnancy must be confirmed before treatment ^[3,4]; the 2009 international 3E recommendations suggest considering a pregnancy test ^[5].
• Vitamin B12 (before folic acid supplementation, especially after 50)if neededThe SmPC recommends measuring vitamin B12 before prescribing folic acid, especially after age 50, as folic acid can mask a deficiency ^[3].
• IGRA (if risk factor for latent tuberculosis)if needednon-French guidelineThe 2025 BSR (British Society for Rheumatology) recommends looking for latent tuberculosis in at-risk patients (origin from or long stay in an endemic area, contact, occupational exposure) before conventional disease-modifying treatment; universal screening is not recommended ^[6].
• Not a laboratory test: chest X-ray (less than a year old); pulmonary function tests if smoker or lung disease.

At 2 weeks

• FBC with platelets
• Serum creatinine with eGFR
• AST
• ALT
• Serum albumin

Then every month for 3 to 6 months

• FBC with platelets
• Serum creatinine with eGFR
• AST
• ALT
• Serum albumin

Every 3 months (more often if risk factor for toxicity)

• FBC with platelets
• Serum creatinine with eGFR
• AST
• ALT
• Serum albumin