A person has unprotected sex 3 weeks back. To rule out HIV infection the best test is-
**Core Concept**
The question is testing the understanding of the window period of HIV infection, which is the time between exposure to the virus and when it can be detected by a test. During this period, the virus may not be present in sufficient quantities to be detected by standard tests.
**Why the Correct Answer is Right**
The correct answer is the test that can detect HIV antibodies and p24 antigen, which is the viral protein that is present in the blood before the body produces antibodies. The p24 antigen test is particularly useful because it can detect the presence of the virus 14-24 days after exposure, which is before the body has produced antibodies. This is important because it allows for early detection and treatment of HIV infection.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a test for hepatitis B, not HIV.
**Option B:** This option is incorrect because it is a test for hepatitis C, not HIV.
**Option C:** This option is incorrect because it is a test for syphilis, not HIV.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the window period for HIV testing can vary depending on the individual and the type of test used. However, the p24 antigen test can detect the virus as early as 14-24 days after exposure, making it a valuable tool in early diagnosis and treatment.
**Correct Answer: D. HIV p24 antigen test**