What laboratory tests and monitoring are required for a patient on Pre-Exposure Prophylaxis (PrEP) with emtricitabine/tenofovir disoproxil fumarate (Truvada) in a specific location?

Laboratory Monitoring for Patients on PrEP

For patients on Truvada PrEP, you must perform HIV testing every 3 months, STI screening at all exposed anatomic sites every 3 months, and renal function monitoring (creatinine clearance) every 6 months, with more frequent renal monitoring (every 3 months) for patients over 50 years old or with baseline kidney function concerns. 1, 2

Pre-Initiation Testing (Before Starting PrEP)

Before prescribing the first dose, obtain these mandatory tests:

• HIV testing with combination antigen-antibody assay (4th generation) – this is mandatory and must be negative before starting 3, 4
• HIV RNA testing – add this if any clinical suspicion of acute HIV infection exists (fever, rash, lymphadenopathy, pharyngitis, or recent high-risk exposure within the past month) 3, 1, 2
• Serum creatinine with calculated creatinine clearance using Cockcroft-Gault formula – do not start if CrCl <60 mL/min 3, 1, 4
• Hepatitis B surface antigen (HBsAg) – essential because stopping TDF in HBV-positive patients can cause severe hepatitis flares 3, 1, 2
• Hepatitis C antibody testing 3, 1, 2
• STI screening at all potentially exposed anatomic sites (oral, rectal, urogenital) for gonorrhea and chlamydia by NAAT, plus syphilis serology 3, 1, 2
• Pregnancy testing for individuals of childbearing potential 3, 1, 2
• Urine glucose and urine protein 4

Ongoing Monitoring Schedule While on PrEP

Every 3 Months (Quarterly Visits)

• HIV testing with combination antigen-antibody assay – this is mandatory and PrEP prescriptions should not exceed 90 days without documented negative HIV testing 3, 1, 2, 4
• Three-site STI screening (rectal, pharyngeal, urogenital) for gonorrhea and chlamydia by NAAT 3, 1, 2, 5
• Syphilis serology 3, 1, 2
• Pregnancy testing for applicable individuals 3, 1, 2
• Adherence assessment and counseling 1, 2
• Risk behavior assessment and condom provision 1

Every 6 Months (Biannual Testing)

• Serum creatinine and estimated creatinine clearance for standard-risk patients 3, 1, 2
• Hepatitis C antibody testing annually, but every 6 months for high-risk individuals (people who inject drugs or MSM who use recreational drugs during sex) 1, 2

Special Monitoring Considerations: More Frequent Renal Testing

Increase renal monitoring to every 3 months for patients with these risk factors: 3, 1, 2

• Age >50 years
• Baseline creatinine clearance <90 mL/min
• Taking hypertension or diabetes medications
• Chronic kidney disease
• Any mild creatinine elevation on previous testing

Research data support this approach, showing that older patients (≥40 years) have 3.9 times greater risk of renal impairment despite similar rates of decline 6, and that mean creatinine clearance declines are greater in those starting PrEP at older ages (-4.2% for ages 40-50 and -4.9% for >50 years) 6.

One-Month Follow-Up Visit

Schedule a visit at 30 days after PrEP initiation to assess for adverse effects, perform follow-up HIV testing, and support adherence 1. This early visit is particularly important for adolescents who may benefit from more frequent counseling 4.

Critical Contraindications and When to Stop PrEP

• Do not prescribe or continue TDF-based PrEP if creatinine clearance falls below 60 mL/min 3, 1, 4
• Do not prescribe TDF-based PrEP for patients with osteopenia or osteoporosis (consider tenofovir alafenamide-based PrEP instead for MSM) 3, 5
• Avoid concurrent use with nephrotoxic agents such as high-dose or multiple NSAIDs 4

If HIV Infection Occurs During PrEP

If HIV infection is suspected while on PrEP (positive screening test, symptoms of acute infection, or high-risk exposure with nonadherence):

• Immediately add a boosted protease inhibitor (ritonavir-boosted darunavir) and/or dolutegravir to the TDF/emtricitabine regimen while awaiting HIV RNA and resistance testing results 3, 1, 2
• Order HIV RNA and genotype resistance testing immediately 1, 2
• Switch to a recommended initial antiretroviral treatment regimen once HIV is confirmed 1, 2, 5

This approach is critical because initiating PrEP during undiagnosed acute HIV can lead to drug resistance, particularly M184V/I mutations 2.

Common Pitfalls to Avoid

• Never prescribe >90-day supplies of PrEP without documented negative HIV testing – this is a critical safety measure to prevent inadvertent monotherapy in someone who seroconverts 1, 2
• Do not discontinue PrEP based solely on mild creatinine elevation if CrCl remains >60 mL/min – check for proteinuria and recheck in 1-3 months, as mild elevations are often transient 2
• Do not refer to nephrology unless proteinuria is significant or CrCl continues declining below 60 mL/min on repeat testing 2
• Do not abruptly discontinue PrEP in patients with chronic hepatitis B without careful monitoring, as this can cause acute hepatitis flares or hepatic decompensation, particularly in those with cirrhosis 3, 1, 4
• Do not use only antibody-based HIV tests – always use combination antigen-antibody assays, as antibody-only tests may miss acute HIV infection 4

Renal Function Monitoring: Practical Approach

Research demonstrates that PrEP causes an initial drop in eGFR of approximately -2.5 mL/min/1.73m² followed by progressive decline of -0.38 mL/min/1.73m² per month 7. However, significant renal impairment (eGFR <70 mL/min/1.73m²) occurs in only 6.5% of patients, with persistent impairment in just 1.0% 7. PrEP discontinuation due to renal concerns is rare (0.4% in one cohort) 7, and renal dysfunction is mostly reversible following discontinuation 7, 8.