What documentation is essential before coding Z21 for asymptomatic infection?

The correct answer is based on the requirement that a healthcare provider's diagnostic statement is necessary to properly code Z21 for asymptomatic infection. This code specifically indicates an asymptomatic carrier of the HIV virus. For accurate coding, it is essential to have documentation from a provider that confirms the diagnosis, which can be based on clinical evaluation and testing. This ensures that the coding reflects the patient's true health status as determined by a qualified medical professional.

Other choices may provide relevant information about the patient's condition, but they do not fulfill the requirement for official coding. For instance, while a patient's HIV symptoms or a positive serologic test could indicate HIV status, coding guidelines emphasize the need for a definitive diagnostic statement from the provider. Family history, on the other hand, does not establish an individual's current health status and would not suffice for coding Z21.