What are the recommended tests and treatment options for diagnosing HIV?

Recommended Tests for HIV Diagnosis

The recommended initial HIV screening test is a combination HIV antibody/p24 antigen test, which has sensitivity and specificity greater than 99.5%, followed by confirmatory testing with Western blot or immunofluorescent assay for positive results. 1, 2

HIV Testing Algorithm

Initial Screening

• Combination HIV antibody/p24 antigen test (preferred initial screening test)

  • Detects both HIV antibodies and p24 antigen
  • Allows earlier detection of HIV infection than antibody-only tests
  • Sensitivity and specificity >99.5%
  • Results available within 1-2 days from commercial laboratories 1

• Rapid HIV testing (alternative for immediate results)

  • Can use blood or oral fluid specimens
  • Results available in 5-40 minutes
  • Sensitivity and specificity >99.5%
  • Positive results require confirmation with conventional methods 1

Confirmatory Testing

For reactive initial screening tests:

1. HIV-1/HIV-2 antibody differentiation immunoassay

   • Differentiates between HIV-1 and HIV-2 antibodies 2

2. If differentiation assay is negative or indeterminate:

   • Nucleic Acid Amplification Test (NAAT) such as HIV RNA PCR
   • Rules out acute HIV infection
   • Detects virus directly rather than antibody response 2

Special Testing Considerations

For Infants and Children <18 Months

• HIV DNA PCR testing is preferred

  • Detects HIV genetic material directly
  • Not affected by maternal antibodies
  • 93% of infected infants test positive by 14 days of age 2

• Recommended testing schedule:

  • Initial test by 48 hours of age
  • Testing at 14 days (if available)
  • Testing at 1-2 months
  • Testing at 3-6 months 2

For Recent Exposures

• Persons with recent known or possible HIV exposure should be tested using:

  • Rapid or laboratory-based Ag/Ab test
  • Consider adding HIV NAT (RNA test) for very recent exposures 1

• Follow-up testing after exposure:

  • Laboratory-based Ag/Ab test AND diagnostic NAT at 4-6 weeks
  • Final HIV testing 12 weeks after exposure 1

Additional Laboratory Tests After HIV Diagnosis

Once HIV infection is confirmed, the following tests should be ordered:

1. CD4 cell count with percentage

   • Assesses immune status and disease progression
   • Baseline for monitoring treatment response 1

2. HIV viral load (HIV RNA level)

   • Establishes baseline viral activity
   • Helps determine need for antiretroviral therapy
   • Used to monitor response to therapy 1

3. HIV genotype testing

   • Assesses for transmitted drug resistance
   • Guides selection of antiretroviral therapy 1

4. Additional screening tests

   • Complete blood count with differential
   • Comprehensive metabolic panel
   • Screening for co-infections (hepatitis, tuberculosis, STIs)
   • HLA-B*5701 testing before abacavir use
   • CCR5 tropism testing if considering maraviroc 1

Recommended Screening Frequency

• All sexually active individuals: At least once in their lifetime 1
• High-risk populations: Every 3-12 months
  • Men who have sex with men
  • Transgender women
  • People who inject drugs
  • Persons with multiple sexual partners 1
• Pregnant women: During each pregnancy 2

Common Pitfalls to Avoid

1. False-negative results during "window period"

   • Antibody tests may be negative during early infection
   • Consider NAT testing for suspected acute infection 1, 3

2. False-positive screening results

   • Can occur with autoimmune disorders or pregnancy
   • Always confirm positive screening tests 1

3. Relying solely on antibody tests for infants <18 months

   • Maternal antibodies persist up to 18 months
   • Use virologic tests (DNA PCR) instead 2

4. Missing acute infections

   • Fourth-generation Ag/Ab tests shorten but don't eliminate window period
   • Consider HIV RNA testing when acute infection is suspected 3

5. Delayed linkage to care

   • Immediately connect diagnosed individuals to HIV care
   • Early treatment improves outcomes and reduces transmission 1