What baseline laboratory tests and follow‑up monitoring schedule should be used for an HIV‑positive patient starting antiretroviral therapy?

Laboratory Monitoring for HIV Patients on Antiretroviral Therapy

For HIV patients starting ART, obtain baseline CD4 count, HIV RNA viral load, resistance testing, complete blood count, comprehensive metabolic panel, fasting lipids, hepatitis B/C serology, and sexually transmitted infection screening, then monitor HIV RNA at 4-6 weeks, every 3 months until suppressed for 1 year, then every 6 months; CD4 monitoring every 6 months until >250 cells/μL for 1 year with viral suppression. 1, 2

Baseline Laboratory Testing

Before initiating ART, the following tests are essential:

HIV-Specific Tests

• CD4 cell count with percentage – establishes immune status and guides prophylaxis decisions 1
• HIV RNA viral load (plasma) – determines baseline viremia and prognosis 1
• HIV genotype resistance testing – identifies transmitted drug resistance in all treatment-naïve patients 1
• HIV serologic confirmation – especially for patients without documentation or tested anonymously 1
• HLA-B*5701 testing – required before prescribing abacavir to prevent hypersensitivity 1
• CCR5 tropism assay – only if considering maraviroc 1

Safety and Comorbidity Screening

• Complete blood count with differential – baseline hematologic assessment 1
• Comprehensive metabolic panel (electrolytes, BUN, creatinine, liver enzymes, bilirubin, albumin, alkaline phosphatase) – assesses organ function 1
• Fasting lipid profile – baseline cardiovascular risk 1, 2
• Hepatitis B surface antigen, hepatitis B core antibody, hepatitis C antibody – screen for coinfections 1, 2
• Syphilis serology (VDRL/RPR) – routine STI screening 1
• Tuberculin skin test or interferon-gamma release assay – TB screening 1
• Toxoplasma IgG serology – guides prophylaxis if CD4 <100 cells/μL 1
• Pregnancy test for women of childbearing potential 1
• Glucose-6-phosphate dehydrogenase – in appropriate ethnic groups before certain medications 1

Critical pitfall: Obtain two baseline CD4 and viral load measurements when possible to account for biological variability, though in advanced disease (CD4 <200 cells/μL), do not delay treatment 1

Follow-Up Monitoring Schedule

HIV RNA Viral Load Monitoring

Early response assessment:

• At 4-6 weeks after ART initiation – assess early virologic response and adherence 1, 2
• Expected decline: approximately 0.5-0.75 log₁₀ copies/mL by 4-8 weeks 1
• Goal: undetectable (<50 copies/mL) by 12-24 weeks, though integrase inhibitor regimens may suppress faster 2

Ongoing monitoring:

• Every 3 months until viral suppression (<50 copies/mL) achieved and maintained for at least 1 year 1, 2
• Every 6 months thereafter if patient remains virologically suppressed, clinically stable, and adherent 1, 2

Important nuance: A substantial change in viral load is defined as ≥3-fold (0.5 log₁₀) increase or decrease 1. Single detectable "blips" <200 copies/mL do not constitute virologic failure and should not prompt regimen change 2

Virologic failure definition: Confirmed HIV RNA >200 copies/mL on two consecutive measurements 2

CD4 Cell Count Monitoring

• Every 6 months until CD4 count consistently >250 cells/μL for at least 1 year with concurrent viral suppression 1, 2
• Discontinue routine CD4 monitoring after sustained CD4 >250 cells/μL for 1 year, unless virologic failure occurs or immunosuppressive conditions develop 2

Key consideration: CD4 percentage is preferred over absolute count in children <5 years due to age-related variability 1. A substantial CD4 decrease is >30% decline in absolute count or >3% decline in percentage 1

Safety Laboratory Monitoring

• Renal function (creatinine, estimated GFR): at baseline and periodically during treatment, especially with tenofovir-containing regimens 2, 3
• Liver function tests: at baseline and as clinically indicated 2
• Fasting lipid panel: baseline and periodically for cardiovascular risk assessment 2
• Complete blood count: baseline and as needed to monitor hematologic toxicity 2
• Serum phosphorus, urine glucose, urine protein: before and during tenofovir therapy in patients at risk for renal dysfunction 3

Additional Screening

• Sexually transmitted infection screening at all exposed mucosal sites (pharyngeal, urethral, rectal) – frequency based on risk 2
• Hepatitis C screening annually for men who have sex with men with ongoing risk 2
• Cervical/anal dysplasia screening – age and risk-appropriate 2
• Opportunistic infection assessment if initial CD4 count was low 2

Critical Pitfalls to Avoid

1. Do not delay initial follow-up beyond 6 weeks – early identification of inadequate response allows timely intervention 2

2. Do not switch ART based on single detectable viral load – isolated blips do not constitute failure; confirm with repeat testing within 4 weeks 1, 2

3. Do not order resistance testing for viral loads <200 copies/mL – amplification unlikely to succeed and does not meet threshold for confirmed failure 2

4. Do not continue indefinite CD4 monitoring once sustained suppression and immune reconstitution achieved – adds unnecessary cost without clinical benefit 2

5. Use same laboratory and assay method for serial viral load measurements to ensure consistency, as different assays have varying thresholds (20-400 copies/mL) 1

6. Avoid viral load testing during or within 4 weeks after acute illness, vaccination, or treatment of intercurrent infections – these transiently increase HIV RNA 1

When Discordance Occurs

Viral load is more informative than CD4 count for guiding ART decisions 1, 4. When CD4 and viral load trends are discordant (occurs in ~20% of patients), prioritize viral load trends but consider expert consultation 1. If HIV RNA has not declined considerably by 4-6 weeks despite adequate adherence, perform genotypic resistance testing 1, 2