What code should be assigned for a patient with an inconclusive HIV test result?

The appropriate code for a patient with an inconclusive HIV test result is R75. This code is specifically designated for "inconclusive laboratory evidence of human immunodeficiency virus (HIV)." An inconclusive test means that the results do not definitively diagnose or rule out HIV infection, thus requiring a specific coding that indicates uncertainty rather than a confirmed diagnosis.

In contrast, the other codes are not suitable for this scenario. B20 refers to "HIV disease" and is used when there is a confirmed diagnosis of HIV. Z21 is used for "asymptomatic human immunodeficiency virus (HIV) infection status," applicable when a patient is confirmed to be HIV positive but does not have any symptoms. Lastly, O98.7 is related to complications of HIV in pregnancy, which is irrelevant to an inconclusive HIV test result. Therefore, R75 is the correct choice, as it specifically captures the notion of inconclusiveness in HIV testing.