Pharmacology · patient case question
Which laboratory test is the essential routine monitor for her METHOTREXATE therapy?
Patient case: Rheumatoid arthritis managed with adalimumab and methotrexate
Patient: Female, 55 years old
Chief Complaint: “I need a crown replaced and my hands make brushing hard.”
Background: Rheumatoid arthritis of eight years' duration. Adalimumab (Humira) every other week and weekly oral methotrexate with folate supplementation. No other medications.
Vital Signs: BP 122/78 mmHg · HR 74 bpm · T 98.1°F
Findings: Symmetric swelling of the metacarpophalangeal and proximal interphalangeal joints with reduced grip strength. Limited mouth opening, 32 mm. Bilateral TMJ crepitus. Generalized plaque accumulation.
Show answer and explanation
Correct answer: A. Complete blood count with differential
- A. CORRECT. Methotrexate is a folate antagonist that suppresses the BONE MARROW, so the COMPLETE BLOOD COUNT WITH DIFFERENTIAL is the test that matters: leukopenia raises infection risk and impairs healing, thrombocytopenia adds bleeding risk, and macrocytic anaemia reflects the antifolate effect. Standard monitoring pairs the CBC with liver function tests and renal function, checked every two to three months once the dose is stable.
- B. A lipid panel has no role in methotrexate monitoring.
- C. Renal function is monitored, because methotrexate is renally cleared and impairment causes accumulation — but creatinine ALONE misses the marrow suppression, which is the effect that determines whether she can safely undergo a procedure.
- D. Calcium and phosphate relate to bone and parathyroid metabolism, not to antifolate toxicity.
Note: What this item adds is the MONITORING test and its interpretation. Two practical points: never prescribe an NSAID alongside methotrexate — NSAIDs reduce its renal clearance and can precipitate toxicity — and remember that adalimumab is a TNF-α inhibitor, so infection risk is compounded and postoperative healing warrants closer review.