What labs are required for individuals on Pre-Exposure Prophylaxis (PrEP) for Human Immunodeficiency Virus (HIV) prevention and at what intervals?

Laboratory Monitoring for HIV PrEP

Individuals on PrEP require HIV testing every 3 months, with renal function monitoring at least every 6 months (more frequently if at risk), and quarterly STI screening to ensure safety and prevent undiagnosed HIV infection. 1

Baseline Testing (Before PrEP Initiation)

Before starting PrEP, the following labs are mandatory to prevent administering PrEP to someone with undiagnosed HIV and to establish safety baselines:

• HIV testing with combined antibody/antigen assay (4th generation test preferred) 1

  • If acute HIV infection is suspected based on symptoms (fever, rash, lymphadenopathy, pharyngitis), add HIV RNA testing and withhold PrEP until results confirm negative status 1
  • For high-risk populations with recent exposure, HIV RNA may be helpful even without symptoms 1

• Serum creatinine and estimated creatinine clearance 1

  • PrEP should not be started if creatinine clearance is <60 mL/min 1

• Hepatitis B surface antigen (HBsAg) 1

  • Critical because discontinuing TDF-based PrEP in HBV-positive patients can cause hepatitis flares or hepatic decompensation, especially with cirrhosis 1

• Hepatitis C antibody 1

• STI screening (genital and extragenital sites as appropriate):

  • Gonorrhea and chlamydia by nucleic acid amplification test (NAAT) 1
  • Syphilis serology 1
  • Test oral, rectal, urine, and vaginal sites based on sexual practices 1

• Pregnancy testing for individuals of childbearing potential 1

• Hepatitis A antibody for MSM and people who inject drugs if not known to be immune 1

Critical caveat: If a combined HIV antibody/antigen test was performed within 7 days and is negative with no symptoms of acute HIV, PrEP can be started same-day without waiting for other baseline results 1. However, rapid follow-up for safety labs is essential.

Follow-Up Monitoring During PrEP

At 1 Month After Initiation

• Combined HIV antibody/antigen test 1
  • This early visit assesses adherence, tolerability, and catches any missed acute infections 1

Every 3 Months (Quarterly)

This is the cornerstone of PrEP monitoring:

• Combined HIV antibody/antigen test (mandatory—PrEP should not be prescribed for >90 days without HIV testing) 1

  • If symptoms of acute HIV develop, order HIV RNA immediately regardless of timeline 1

• STI screening (genital and extragenital):

  • Gonorrhea and chlamydia NAAT 1
  • Syphilis serology 1
  • Adjust frequency based on individual risk 1

• Pregnancy testing for individuals of childbearing potential 1

• Estimated creatinine clearance at the first quarterly visit only, then annually thereafter 1

Every 6-12 Months

• Creatinine and estimated creatinine clearance annually for standard-risk patients 1

• Hepatitis C antibody annually 1

  • Test every 3-6 months for people who inject drugs or MSM who use recreational drugs during sex 1
  • If transaminases are elevated, test more frequently and consider acute HCV 1

High-Risk Patients Requiring More Frequent Renal Monitoring

Monitor creatinine every 3-6 months (not annually) for patients with: 1

• Age >50 years
• Baseline creatinine clearance 60-90 mL/min
• Diabetes
• Hypertension
• Other comorbidities predisposing to kidney dysfunction

The 2020 IAS-USA guidelines emphasize this more frequent monitoring because TDF can cause reversible glomerular dysfunction, though bone mineral density loss (1-1.5% at 48 weeks) returns to baseline after discontinuation 1.

Special Monitoring Situations

If PrEP is Stopped for ≥7 Days

• Repeat combined HIV antibody/antigen test before restarting PrEP 1
  • This prevents restarting PrEP during an undiagnosed acute infection acquired during the gap

If HIV Infection Occurs on PrEP

• Immediate HIV RNA and genotype resistance testing 1
• Add a boosted protease inhibitor (darunavir/ritonavir) and/or dolutegravir to the TDF/emtricitabine while awaiting resistance results 1
• Resistance is rare but most commonly M184V/I, typically when PrEP was started during occult acute infection 1, 2, 3

Injectable Cabotegravir PrEP

For long-acting injectable cabotegravir (600 mg IM every 8 weeks after initial 4-week interval): 1

• Rapid point-of-care HIV test on the day of each injection before administering the injection
• Combined antibody/antigen testing should still occur but timing differs from oral PrEP protocols

Common Pitfalls to Avoid

1. Never prescribe PrEP for >90 days without interval HIV testing—this is when resistance can develop if acute infection is missed 1

2. Do not skip HIV RNA testing if acute HIV is suspected—antibody/antigen tests can be negative during the eclipse phase 1, 2

3. Do not forget to monitor renal function more frequently in older patients or those with baseline kidney issues—waiting a full year could miss progressive dysfunction 1

4. Do not overlook extragenital STI screening—pharyngeal and rectal gonorrhea/chlamydia are common in MSM and often asymptomatic 1

5. Do not discontinue TDF-based PrEP abruptly in HBV-positive patients without close monitoring—hepatitis flares can be severe 1