What labs and frequency are required for Pre-Exposure Prophylaxis (PrEP)?

PrEP Laboratory Monitoring Requirements

For PrEP, perform HIV testing every 3 months, renal function testing at 3 months then every 6 months (or every 3-6 months if high-risk), STI screening quarterly, and hepatitis C testing annually. 1

Baseline Testing (Before Starting PrEP)

Before initiating PrEP, the following labs are mandatory:

• HIV testing: Combined HIV antibody/antigen test (4th generation) to confirm HIV-negative status 1

  • If acute HIV infection is suspected (recent high-risk exposure or symptoms), add HIV RNA testing 1
  • Do not start PrEP until HIV RNA confirms negative status if acute infection is suspected 1

• Renal function: Serum creatinine with calculated creatinine clearance (must be ≥60 mL/min) 1

• Hepatitis B surface antigen (HBsAg): Screen for active hepatitis B infection 1

  • Critical because stopping TDF/emtricitabine in HBsAg-positive patients can cause hepatitis flares or hepatic decompensation 1

• Hepatitis C antibody: Screen at baseline 1

• STI screening: Test for gonorrhea and chlamydia (genital and extragenital sites by NAAT) and syphilis 1

• Pregnancy test: For individuals of childbearing potential 1

Follow-Up Monitoring Schedule

At 1 Month After Initiation

• HIV antibody/antigen test: Confirm HIV-negative status and assess for acute infection 1
• Adherence assessment and adverse effects evaluation 1

Every 3 Months (Quarterly Visits)

• HIV antibody/antigen testing: Mandatory at every quarterly visit 1

  • PrEP prescription should not exceed 90 days without HIV testing 1

• STI screening: Test for gonorrhea, chlamydia (genital and extragenital), and syphilis 1

• Pregnancy testing: For individuals of childbearing potential 1

• Renal function at first quarterly visit: Calculate estimated creatinine clearance 1

Every 6 Months

• Renal function: Measure serum creatinine and calculate creatinine clearance 1

  • Exception: Monitor every 3-6 months for high-risk patients including those aged >50 years, baseline eGFR <90 mL/min, or comorbidities like diabetes or hypertension 1

• Bacterial STI screening: If not already done quarterly 1

Annually

• Hepatitis C antibody testing: Screen at least once yearly 1

  • Exception: Test every 3-6 months for people who inject drugs, MSM using recreational drugs during sex, or those with elevated transaminases 1

• Renal function: Annual creatinine clearance if not in high-risk category 1

Critical Monitoring Caveats

Renal function monitoring is particularly important because TDF can cause proximal tubular dysfunction and decreased eGFR 2. The risk is substantially higher in patients aged ≥50 years (hazard ratio 13-14.7) and those with baseline eGFR <90 mL/min (hazard ratio 28.9-34) 3, 4.

For patients with active hepatitis B, never discontinue TDF/emtricitabine abruptly without careful monitoring, as this can precipitate acute hepatitis flares or hepatic decompensation, especially in those with cirrhosis 1.

If HIV testing is missed for 7+ consecutive days after stopping PrEP, repeat combined HIV antibody/antigen testing before restarting 1.

Same-day PrEP initiation is reasonable if rapid HIV test is negative and patient is asymptomatic, without waiting for baseline labs (creatinine, HBsAg, STI results), as long as these are drawn and results reviewed promptly 1.