A nurse is teaching a female adult client who has a new prescription for azathioprine to treat active rheumatoid arthritis. The nurse should inform the client about the need for which of the following diagnostic tests prior to starting the medication?

A. Bone density scan: Bone density scans assess for osteoporosis risk but are not required before starting azathioprine. They are unrelated to the medication’s safety profile. B. Pregnancy test: Azathioprine can be teratogenic, posing risks to a developing fetus. A pregnancy test is essential before initiating therapy to ensure the client is not pregnant and to guide safe use of the medication. C. Electrocardiogram: ECGs are used to assess cardiac function and detect arrhythmias. Azathioprine does not typically affect cardiac conduction, so this test is not required prior to therapy. D. HbA1c: HbA1c measures long-term blood glucose control for diabetes management. It is not necessary for assessing safety before starting azathioprine for rheumatoid arthritis.