HIV Diagnosis and Treatment Guidelines
Diagnostic Testing Algorithm
- The Centers for Disease Control and Prevention recommends beginning with a sensitive screening test, such as enzyme-linked immunosorbent assay (ELISA) or rapid HIV test, for HIV diagnosis 1
- Informed consent must be obtained before performing HIV testing, as per the Centers for Disease Control and Prevention guidelines 2, 3
- All reactive screening tests must be confirmed by Western blot or indirect immunofluorescence assay (IFA) before being considered definitive, according to the Centers for Disease Control and Prevention 2, 1
- If confirmatory testing results are negative or indeterminate, follow-up testing should be performed on a blood specimen collected 4 weeks after the initial reactive test, as recommended by the Clinical Infectious Diseases society 4
- Antibody tests cannot rule out infection that occurred less than 6 months before the test, as HIV antibody is detectable in ≥95% of patients within 6 months of infection, according to the Centers for Disease Control and Prevention 2, 3
Special Considerations
- For infants <15 months born to HIV-positive mothers, definitive diagnosis should be based on laboratory evidence of HIV in blood or tissues by culture, nucleic acid, or antigen detection, as per the Centers for Disease Control and Prevention guidelines 2, 3
- HIV-2 testing should be considered in persons from endemic regions or their sexual partners, according to the Centers for Disease Control and Prevention 2, 3
- Testing for HIV-2 is recommended when there is clinical evidence of HIV disease but negative HIV-1 antibody tests, as per the Centers for Disease Control and Prevention guidelines 3
Post-Diagnosis Protocol
Medical Evaluation
- All persons with positive HIV tests must receive comprehensive medical evaluation or be referred for these services, as recommended by the Centers for Disease Control and Prevention 2, 3
- Early intervention is critical even for asymptomatic patients, as persons newly diagnosed may be at different stages of infection, according to the Centers for Disease Control and Prevention 2, 3
- Immune function should be monitored through CD4 count and viral load testing to determine disease progression and treatment needs, as per the Centers for Disease Control and Prevention guidelines 3
Psychosocial Support
- Behavioral and psychosocial services should be provided as an integral part of HIV care, according to the Centers for Disease Control and Prevention guidelines 2, 3
- Patients should be helped to navigate challenges including accepting potential life implications, coping with stigma, developing strategies for maintaining physical and emotional health, and initiating behavioral changes to prevent HIV transmission, as recommended by the Centers for Disease Control and Prevention 2, 3
Common Pitfalls and Caveats
- False-negative results can occur during the "window period" (recent infection within 6 months), as per the Centers for Disease Control and Prevention guidelines 2, 3
- Never disclose a positive HIV diagnosis without confirmatory testing, as false positives can occur with screening tests, according to the Centers for Disease Control and Prevention and Clinical Infectious Diseases society guidelines 2, 1
HIV Confirmatory Testing
Introduction to HIV Testing Algorithms
- The Centers for Disease Control and Prevention (CDC) recommends a newer algorithm for HIV testing that does not require Western blot for most cases, starting with a fourth-generation HIV antigen/antibody combination assay for initial screening, followed by an HIV-1/HIV-2 antibody differentiation immunoassay if reactive, and then viral load and CD4 testing for management if the differentiation assay is positive 5
Modern Testing Algorithm
- The CDC and Association of Public Health Laboratories recommend an initial screening using a fourth-generation HIV antigen/antibody combination assay, which detects both HIV antibodies and p24 antigen, and if reactive, perform an HIV-1/HIV-2 antibody differentiation immunoassay to distinguish between HIV-1 and HIV-2 5
- If the differentiation assay is positive, it confirms HIV infection, and if negative, a qualitative or quantitative nucleic acid amplification test (NAAT/HIV RNA) should be performed to rule out acute HIV-1 infection 5
Traditional Testing Algorithm
- The traditional approach, still valid, uses an enzyme immunoassay (EIA/ELISA) for HIV-1/HIV-2 antibodies as the initial screening, followed by confirmatory testing with Western blot if repeatedly reactive, and a positive Western blot confirms HIV infection 6
- A negative Western blot result indicates the person is considered uninfected, unless acute infection is suspected, and an indeterminate Western blot result requires follow-up testing at 4-6 weeks and consideration of HIV RNA testing 6, 7
Alternative Confirmatory Methods and Critical Pitfalls
- Immunofluorescence assay (IFA) can be used as an alternative supplemental test, with positive and negative results interpreted similarly to Western blot, but indeterminate IFA results require Western blot testing for resolution 8, 9
- Never diagnose HIV based on a screening test alone, as all reactive screening tests must be confirmed before diagnosis, and false-positive screening results can occur, with devastating psychological and social consequences 6
Special Populations and Post-Confirmation Requirements
- For infants under 15-18 months born to HIV-positive mothers, standard antibody tests are unreliable due to maternal antibody transfer, and definitive diagnosis requires two positive HIV RNA PCR or viral culture tests on separate specimens 6
- HIV-2 testing should be considered in persons from endemic regions, their sexual partners, or when clinical evidence suggests HIV disease but HIV-1 tests are negative, and if HIV-2 EIA is repeatedly reactive with negative/indeterminate HIV-1 Western blot, send specimen to state public health laboratory for HIV-2 supplemental testing 8, 9
Confirmatory Testing for HIV Diagnosis
Introduction to Confirmatory Testing
- If the HIV-1/HIV-2 antibody differentiation immunoassay is indeterminate, proceed to Step 3, as recommended by the MMWR Recommendations and Reports 10
Special Considerations for PrEP Users
- PrEP use can attenuate or delay HIV seroconversion in diagnostic assays, and reactive results may represent true infection or false positives, as reported in JAMA 11
- Management of PrEP users with reactive results depends on pre-test probability and may range from stopping PrEP for 3-4 weeks and retesting, to intensifying to full ART if clinical suspicion is high, according to JAMA 11
Confirmatory HIV Testing Recommendations (CDC, MMWR 1992)
Traditional Confirmatory Testing
- A repeatedly reactive ELISA must be confirmed with a Western blot before a definitive HIV diagnosis can be made (CDC recommendation) 12, 13, 14.
- A positive Western blot result confirms HIV infection and establishes the diagnosis (CDC recommendation) 12, 13.
- When the Western blot is indeterminate and the HIV‑2 enzyme immunoassay is not repeatedly reactive, the specimen is classified as indeterminate and requires further evaluation (CDC recommendation) 12, 13.
Alternative Confirmatory Methods
- An immunofluorescence assay (IFA) may be used in place of a Western blot for confirmatory testing (CDC recommendation) 12, 13.
- Positive and negative IFA results are interpreted in the same manner as Western blot results for confirming or excluding HIV infection (CDC recommendation) 12, 13.
Retesting Protocol
- For individuals with a positive Western blot result on first testing, a second specimen should be tested to exclude contamination or laboratory error (CDC recommendation) 12, 13, 14.