A patient comes to the hospital with a history of a sore throat, diarrhoea and sexual contact 2 weeks before. The best investigation to rule out HIV is –
**Core Concept**
The patient's symptoms and recent sexual contact raise concern for a sexually transmitted infection (STI), with HIV being a potential cause. Early diagnosis and treatment of HIV are crucial to prevent disease progression and transmission to others.
**Why the Correct Answer is Right**
The best investigation to rule out HIV in this patient would be a fourth-generation HIV antibody and antigen test. This test detects both antibodies and p24 antigen, which is the core protein of the virus. The presence of p24 antigen indicates an acute infection, and the detection of antibodies confirms a past exposure. This test is more sensitive than earlier generations of tests and can detect HIV infection earlier, typically within 14-24 days after exposure.
**Why Each Wrong Option is Incorrect**
**Option A:** A complete blood count (CBC) may show nonspecific abnormalities in HIV infection, but it is not a specific test for diagnosing HIV.
**Option B:** A throat culture may help diagnose pharyngitis, but it is not a reliable test for ruling out HIV.
**Option C:** Stool examination may show gastrointestinal symptoms, but it is not a specific test for diagnosing HIV.
**Clinical Pearl / High-Yield Fact**
It is essential to note that HIV testing should be performed in a confidential and non-judgmental setting to encourage patients to disclose their risk factors and undergo testing.
**Correct Answer:** D.