A patient on methotrexate for rheumatoid arthritis — before prescribing dental procedures, what blood test is most important to monitor?

Correct answer: C. Creatinine clearance (kidney function)

• A. Platelet count may be affected by methotrexate (myelosuppression) but creatinine clearance is the most critical specific test for methotrexate monitoring.
• B. INR monitors warfarin therapy — not methotrexate.
• C. Correct. Methotrexate can cause nephrotoxicity (kidney damage). Creatinine clearance (or serum creatinine/eGFR) monitors renal function, which is critical because methotrexate is renally excreted — impaired kidney function leads to drug accumulation and toxicity. Monitoring kidney function is essential for methotrexate safety.
• D. HbA1c monitors diabetes — not relevant to methotrexate monitoring.