HIV Test

Aka: HIV Test, HIV Antibody, HIV Screening, HIV Labs

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II. Indications

  1. See HIV Screening Indications

III. Labs: HIV Diagnosis (2014 U.S. protocol)

  1. Step 1: HIV-1/HIV-2 EIA Antibody Test with p24 Antigen testing (fourth generation)
    1. Negative
      1. No HIV-1 or HIV-2 Antibody or p24 Antigen
      2. p24 Antigen is detectable by HIV Testing as early as 2 weeks after infection
      3. High Negative Predictive Value
      4. Retest in 2-4 weeks if new HIV Exposure in prior 2 weeks
    2. Positive
      1. Go to Step 2 for discriminatory assay
  2. Step 2: HIV-1/HIV2 Discriminatory Assay (Multispot)
    1. Negative for HIV-1 and HIV-2
      1. Go to step 3 for confirmatory, NAAT testing
      2. If NAAT Test not available, then report as HIV Indeterminate
    2. HIV-1 Antibody positive (most common in U.S.)
      1. Obtain viral load
      2. Start Combination Antiretroviral Therapy
    3. HIV-2 Antibody positive (West Africa, nRTI resistance)
      1. Start Combination Antiretroviral Therapy
  3. Step 3: HIV-1 RNA Nucleic Acid Amplification Test (NAT or NAAT) for HIV RNA Viral Activity
    1. Negative NAAT
      1. Retest in 2-4 if new HIV Exposure in prior 2 week
    2. Positive NAAT
      1. Acute HIV Infection (although rare False Positive tests occur)
      2. Start Combination Antiretroviral Therapy

IV. Labs: Timing of HIV Test detection (from transmission)

  1. Days 10-12 (1-2 weeks)
    1. HIV 1 Nucleic Acid amplification test (NAAT) for HIV RNA Viral Activity positive
  2. Days 15-17 (2 weeks)
    1. HIV p24 Antigen positive
  3. Day 21 (3 weeks)
    1. HIV-1/HIV-2 EIA Test (fourth generation) positive
  4. Day 28 (4 weeks)
    1. HIV-1/HIV2 Discriminatory Assay (Multispot)
  5. Day >35 (5 weeks)
    1. Unigold OraQuick positive
    2. HIV Western Blot positive
  6. References
    1. Masciotra (2011) J Clin Virol 52(Suppl 1):S17-22 [PubMed]

V. Labs: HIV Screening

  1. First line screening (recommended)
    1. Combined HIV-1/HIV-2 EIA Antibody and p24 Antigen Immunoassay (fourth generation test)
  2. Other HIV rapid Screening Tests (office based, perform Multispot/NAAT testing if positive)
    1. Uni-Gold Recombigen
    2. Alere Determine
      1. Rapid finger-stick test detects p24 Antigen and detects and distinguishes HIV-1 and HIV-2 Antibody
      2. Approved in U.S. by FDA in 2013
    3. OraQuick (oral swab based)
      1. Available as In-Home HIV Test as of 2013
      2. Approved for age 17 years old and older
      3. Results in 20-40 minutes
      4. Test Sensitivity
        1. Approaches 99% when performed in clinic
        2. Drops to 92% (False Negative Rate: 1 in 12) when performed at home (due to user error)
      5. Test Specificity: 99.98% (False Positive Rate: 1 in 5000)
      6. Most accurate at 3 months after exposure

VI. Labs: HIV Tests (confirmatory, discriminatory and activity tests)

  1. CD4 Cell Count
    1. Best marker of HIV-related Immunosuppression, infection duration and prognosis
    2. Varies from person to person, lab to lab, by time of day, and most significantly by acute comorbid illness
  2. HIV Enzyme Linked Immosorbent Assay (EIA, ELISA) Antibody Test
    1. Combined with p24 for increased Test Sensitivity
    2. Positive at 3-8 weeks after exposure
    3. Initial False Negative tests in first 2 weeks
    4. Test Sensitivity: 99.5%
    5. False Positive risk and requires confirmatory testing (e.g. HIV )
  3. HIV-1/HIV2 Discriminatory Assay (Multispot)
    1. Detects circulating antibodies to both HIV-1 and HIV-2
    2. Discriminates between HIV-1 and HIV-2
  4. HIV-1 RNA Nucleic Acid Amplification Test (NAT or NAAT) for HIV RNA Viral Activity (HIV Viral Load)
    1. Test Sensitivity: 100% sensitive
    2. Test Specificity: 97.4% Specific
    3. Positive at 11-12 days from infection
    4. Higher rate of False Positives
    5. Low counts (<10,000) are often False Positives
  5. p24 Antigen (direct detection)
    1. Positive at 14-15 days from infection (falls within 6-8 weeks)
    2. Used as part of screening protocol (see above)
    3. Consider for Acute Retroviral Syndrome diagnosis
    4. Test Sensitivity: 88.7% (high False Negative Rate)
    5. Test Specificity: 100%
    6. (2001) Ann Intern Med 134:25-29 [PubMed]
  6. HIV Western Blot Assay
    1. Detects HIV Antigens (p24, gp41, gp120, gag, pol, env Proteins)
    2. Used as a second-line confirmatory test for first generation HIV Tests
    3. Used as a third-line confirmatory tests for 4th generation combination HIV-1/HIV-2/p24 tests
      1. Obtained if second-line Multispot or NAAT testing is negative, but initial testing positive

VII. Efficacy: False-negative HIV Test causes (Consider repeat testing or HIV Viral Load testing)

  1. Acute seroconversion (<4 weeks of HIV Infection)
  2. Advanced AIDS (Antibody based tests)
  3. Autoimmune Condition
  4. Hemodialysis patients (Renal Failure)
  5. Multiple pregnancies
  6. Multiple transfusions
  7. Cystic Fibrosis
  8. Liver disease
  9. Intravenous Drug Abuse
  10. Immunization
    1. HIV Vaccination (experimental only)
    2. Recent other Immunization

VIII. Labs: Related Sexually Transmitted Disease Testing

  1. Syphilis Serology (Rapid Plasma Reagin, VDRL)
  2. Hepatitis B Serology
  3. Hepatitis C Serology
  4. Gonorrhea Culture
  5. Chlamydia Antigen

IX. Labs: Disease Screening Related to Advanced HIV or AIDS

  1. Tuberculin Skin Test (PPD, Mantoux)
    1. Consider Quantiferon-TB instead
    2. Dose: 0.5 cc injected (contrast with standard 0.1 cc)
    3. Positive: >5 mm (contrast with standard 10 mm)
  2. Cytomegalovirus Serology (CMV)
  3. Toxoplasmosis Titer
  4. Gynecologic examination with Pap Smear
    1. HIV associated with advanced Cervical Cancer

X. References

  1. (1997) Med Lett Drugs Ther 39:81-3 [PubMed]
  2. Mylonakis (2000) Arch Intern Med 160:2386-8 [PubMed]
  3. Sherin (2014) Am Fam Physician 89(4): 265-72 [PubMed]

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