A patient with rheumatoid arthritis takes methotrexate and adalimumab. Which laboratory investigation is MOST important before invasive dental treatment?

Correct answer: D. A complete blood count with differential

• A. Thyroid function is unrelated to methotrexate or anti-TNF therapy.
• B. A lipid panel has no bearing on dental treatment risk in this patient.
• C. Electrolytes alone do not assess the marrow suppression that is the primary concern.
• D. CORRECT. Methotrexate is a folate antagonist that causes MYELOSUPPRESSION (leukopenia, thrombocytopenia, anemia) and mucositis; adalimumab is a TNF-alpha inhibitor causing further IMMUNOSUPPRESSION and infection risk. A CBC WITH DIFFERENTIAL reveals the absolute neutrophil count (infection risk) and the platelet count (bleeding risk) — the two parameters that directly change dental management. Methotrexate also requires periodic renal (creatinine) and hepatic monitoring, so a comprehensive metabolic panel is a reasonable adjunct.

Note: Both are part of routine methotrexate monitoring (CBC + LFTs + creatinine). For DENTAL decision-making the CBC is the one that changes management (ANC and platelets). Discuss with the group.