Short answer
PrEP is HIV prevention medication for people who do not have HIV. Before starting, CDC clinical guidance says HIV status must be confirmed, and baseline care commonly includes STI screening, kidney function checks for oral PrEP, hepatitis B screening for oral PrEP, and cholesterol or triglyceride checks for some PrEP options. During PrEP, repeat HIV testing and STI follow-up are not optional details; they are how PrEP stays safe and effective.
Common PrEP labs and checks
| Lab or check | Why it matters | Important caveat |
|---|---|---|
| HIV antigen/antibody and HIV-1 RNA testing | Confirms a person does not have HIV before starting or continuing PrEP. | CDC says ambiguous or discordant results need repeat blood testing before PrEP status is settled. |
| Chlamydia, gonorrhea, and syphilis screening | CDC recommends screening sexually active adults for these STIs before starting oral or injectable PrEP. | Body sites matter: urine, vaginal, rectal, oral, or blood tests may be needed depending on exposure. |
| Serum creatinine and estimated creatinine clearance | Oral PrEP with tenofovir-containing medication requires kidney function assessment before starting and periodically after. | CDC says kidney assessments are not necessary for injectable cabotegravir. |
| Hepatitis B screening | Emtricitabine and tenofovir can affect hepatitis B. Stopping oral PrEP without follow-up can be risky for people with active HBV. | CDC says HBV infection is not a PrEP contraindication, but people considered for oral PrEP must be screened. |
| Cholesterol and triglycerides | CDC says these should be assessed before F/TAF oral PrEP and monitored during use. | This is not the same requirement for every PrEP option. |
| Symptoms and medication review | Acute HIV symptoms, STI symptoms, kidney risks, pregnancy questions, drug interactions, and adherence all affect the plan. | A lab schedule cannot replace a clinician conversation when symptoms or exposure timing changes. |
Oral PrEP follow-up schedule
CDC says oral PrEP should be prescribed as part of a combination prevention plan with ongoing assessments. At least every 3 months, CDC lists repeat HIV antigen/antibody and HIV-1 RNA testing, assessment for acute HIV symptoms, adherence and risk-reduction support, and STI testing for symptoms or selected recurrent-risk situations. At least every 6 months, CDC lists kidney monitoring for people age 50 or older or with lower baseline eCrCl, plus STI screening for sexually active people. At least every 12 months, CDC lists eCrCl monitoring for all people continuing oral PrEP and cholesterol, triglyceride, and weight monitoring for people prescribed F/TAF.
Injectable PrEP follow-up schedule
For injectable cabotegravir PrEP, CDC describes HIV antigen/antibody and HIV-1 RNA testing at the 1-month visit after the initial injection and then at least every 2 months beginning in month 3. CDC also lists bacterial STI screening for gay and bisexual men at least every 4 months beginning in month 3, and STI screening for all heterosexually active people at least every 6 months beginning in month 7.
Why HIV testing is repeated so often
PrEP is for people without HIV. CDC says oral rapid tests should not be used to screen for HIV when considering starting or continuing PrEP because they are less sensitive than blood tests and may not detect recent HIV infection. If a person starts or continues PrEP while early HIV infection is missed, drug resistance can become a concern. For timing basics, see the HIV testing window period guide.
PrEP does not replace STI testing
PrEP helps prevent HIV when taken or injected as prescribed, but it does not prevent syphilis, chlamydia, gonorrhea, herpes, hepatitis, HPV, trichomoniasis, BV, yeast, or other infections. If oral or anal sex is part of the exposure history, throat or rectal swabs may be needed; a urine-only test may miss exposed sites. For body-site testing, see the extragenital STI testing guide.
What to ask before starting or continuing PrEP
- Which PrEP option am I using: F/TDF, F/TAF, or injectable cabotegravir?
- Which HIV tests are being used today, and do I need HIV-1 RNA testing?
- Which STI tests are being done, and which body sites are included?
- Do I need serum creatinine, eCrCl, urinalysis for protein, or other kidney follow-up?
- Was hepatitis B screening done, and do I need hepatitis B vaccination or liver follow-up?
- If I am using F/TAF, are cholesterol, triglycerides, and weight being monitored?
- What happens if I miss pills, miss an injection, stop PrEP, or have possible HIV exposure?
Related Lab Intel guides
For broad STI testing, start with the STI testing guide. For HIV timing, see the HIV testing window period guide. For urgent exposure timing, see the PrEP vs PEP testing timelines guide. For condom decisions with a partner, see the STI testing before stopping condoms guide. For recurring testing with multiple partners, see the open relationship and multiple-partner testing guide. For hepatitis markers, see the hepatitis B and C testing guide. For kidney markers, see the kidney function tests guide. For cholesterol and triglycerides, see the lipid panel guide. For DoxyPEP follow-up, see the DoxyPEP and STI testing guide. For affordable care, see the free and low-cost STI testing guide.