Baseline Laboratory Testing Required When Starting PEP
At PEP initiation, you must obtain HIV testing to exclude pre-existing infection, baseline renal and liver function tests, and testing for other sexually transmitted infections based on exposure circumstances. 1
Required HIV Testing at Baseline
The primary goal is to rule out pre-existing HIV infection without delaying PEP initiation:
- Perform a rapid (point-of-care) or laboratory-based HIV antigen/antibody (Ag/Ab) test immediately 1
- If using a rapid test, also order a laboratory-based Ag/Ab test to increase sensitivity for detecting HIV 1
- Consider adding an HIV nucleic acid test (NAT) if the patient has recently taken oral antiretrovirals or received cabotegravir injection within the past year 1
Critical Timing Consideration
Do not delay PEP initiation while waiting for HIV test results 1. If results will not be available during the initial evaluation, start PEP immediately based on the assumption that the exposed person is HIV-negative. PEP can be discontinued later if the patient is found to have HIV infection. 1
Required Baseline Organ Function Tests
Obtain baseline renal and liver function tests before starting PEP 1. These are essential because:
- Antiretroviral medications can cause renal and hepatic toxicity 1
- Pre-existing renal or hepatic disease may require regimen modification 1
- Baseline values are needed to monitor for drug-related toxicities during the 28-day course 1
Additional Testing Based on Exposure Type
Test for other sexually transmitted infections when the exposure involves sexual contact 1:
- Screen for chlamydia, gonorrhea, and trichomonas (in women) or chlamydia and gonorrhea (in men) 1
- Consider presumptive STI treatment, particularly in sexual assault cases where follow-up may be challenging 1
- Assess hepatitis B immune status and consider postexposure hepatitis B vaccination with or without hepatitis B immunoglobulin as indicated 1
Source Person Testing (When Possible)
Attempt to obtain HIV testing from the source person if available and consent is granted 1:
- A fourth-generation HIV antigen-antibody test is preferred because it can detect recent infection earlier than standard antibody tests 1
- If the source person tests negative and has no signs/symptoms of acute HIV infection, PEP is not indicated 1
- However, do not delay PEP initiation while attempting to obtain source person testing or risk factor assessment 1
Common Pitfalls to Avoid
- Never use oral fluid-based rapid HIV tests for PEP screening as they are less sensitive for detecting acute or recent infection than blood tests 1
- Do not wait for laboratory results before starting PEP - the 72-hour window for effectiveness is critical 1
- Remember that inability to provide HIV NATs should not prevent provision of PEP - use the most sensitive accessible HIV test available 1
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