What are the recommended intervals for HIV testing after exposure?

From the Guidelines

HIV testing after exposure should be conducted at specific intervals, including initial testing as soon as possible, followed by testing at 4-6 weeks, 3 months, and sometimes 6 months post-exposure, as recommended by the most recent guidelines 1. The recommended intervals for HIV testing after exposure are crucial to ensure accurate detection of the virus.

• Initial testing should occur as soon as possible after exposure to establish a baseline.
• Testing at 4-6 weeks is critical, as most modern HIV tests can detect infection by this point.
• The 3-month test is considered definitive for most people, as approximately 99% of individuals will have detectable antibodies by this time.
• In some cases, testing at 6 months may be necessary. The window period, which is the time between infection and when tests can detect it, varies based on the type of test used:
• Nucleic acid tests (NATs) can detect HIV in 10-33 days.
• Antigen/antibody tests can detect HIV in 18-45 days.
• Antibody tests can detect HIV in 23-90 days after infection. For those taking post-exposure prophylaxis (PEP), testing should continue for 3 months after completing the 28-day medication course, as PEP can delay antibody production 1. It's essential to note that the guidelines for HIV testing after exposure are based on the latest research and recommendations from reputable health organizations, such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) 1. However, the most recent and highest-quality study should be prioritized when making a definitive recommendation, which in this case is the 2016 study published in JAMA 1.

From the Research

Recommended Intervals for HIV Testing After Exposure

The recommended intervals for HIV testing after exposure vary depending on the type of test used and the individual's circumstances.

• For laboratory-based combination tests that detect both HIV antibody and antigen, a follow-up period of 6 weeks after possible HIV-1 exposure is recommended 2.
• If point-of-care rapid HIV tests are used, a follow-up period of 8 weeks is recommended due to the insufficient sensitivity of currently available rapid tests for detecting HIV-1 antigen 2.
• For HIV-2 exposure, a follow-up period of 12 weeks is recommended since presently used assays do not include HIV-2 antigens and limited information is available on the development of HIV antibodies during early HIV-2 infection 2.

Factors Influencing Testing Intervals

Several factors can influence the recommended testing intervals, including:

• The type of HIV test used, with different tests having varying window periods 3.
• The use of pre- or post-exposure prophylaxis, which can affect the timing of testing 2.
• The individual's age, with different testing algorithms recommended for infants and young children 4.
• The presence of symptoms or other laboratory evidence of HIV infection, which can inform the interpretation of test results 4.

Estimated Window Periods for Different Tests

Studies have estimated the window periods for different HIV tests, including:

• Laboratory screening tests that detect both antigen and antibody, with a 99th percentile window period of 44 days 3.
• Western blot tests, with a 99th percentile window period of 65 days 3.
• The mean eclipse period, estimated to be 8-10 days 5.