Final answer:
Before starting PrEP with emtricitabine/tenofovir disoproxil, an HIV test is essential to ensure the patient is not already HIV-positive, and a creatinine clearance test is necessary to evaluate renal function for baseline and ongoing monitoring.
Step-by-step explanation:
Before prescribing pre-exposure prophylaxis (PrEP) with emtricitabine/tenofovir disoproxil (Truvada), clinicians must ensure that the patient is not already HIV-positive and must establish baseline renal function. The critical lab test that should be done no more than 7 days before starting PrEP is an HIV test, specifically an HIV antibody test using indirect ELISA or a fourth-generation antigen/antibody test, which can detect both HIV antibodies and p24 antigen. It is essential to wait a minimum of three weeks after a potential exposure to minimize the risk of false negatives due to the seroconversion window, typically about three weeks, although in some cases, it can exceed two months.
Additionally, a patient's renal function should be evaluated through a creatinine clearance test as emtricitabine/tenofovir disoproxil can affect kidney health and baseline function needs to be known to monitor for potential drug-induced nephrotoxicity. Following these recommendations ensures that PrEP is safely and appropriately prescribed, contributing to effective HIV prevention.