Comprehensive Guide to HIV Testing and Results Interpretation

1. HIV Diagnosis Jose-Luis Burgos, MD, AAHIVM Prevenmed-UCSD International Heath & Cross Cultural Medicine

2. “Appearances to the mind are of four kinds. Things either are what the appear to be; or they neither are, nor appear to be; or they are, and do not appear to be; or they are not, yet appear to be. Rightly to aim in all these cases is the wise man’s task.” Epicteus, 2nd Century A.D.

3. Objectives • Demonstrate knowledge about current HIV testing methods and interpretation of results • Ability to understand how a VCT program can prevent HIV transmission • Distinguish what tests are useful in infants • Identify rapid tests and their use in high risk and vulnerable population

4. Typical Course of Primary HIV 1 mil HIV RNA 100,000 + HIV RNA HIV-1 Antibodies _ 10,000 Ab P24 + 1,000 Exposure 100 Symptoms 10 0 20 30 40 50 Days

5. Basic Principles of HIV testing • All persons receiving an HIV test should receive counseling for risk reduction before and after an HIV testing • Positive results need to be referred for initial evaluation. • HIV tests should be voluntary and with informed consent

6. Many patients at highest risk for HIV have not been tested • Up to one third of patients receive their first HIV test within two months of an AIDS defining illness • 40% of patients undergoing HIV testing do not return for results • ARV, Prevention of OI, effective interventions

7. Risk Assessment • Tuberculosis • Sexually transmitted disease • Behavioral risk factors • Sexual contact with commercial sex workers, injection drug users, multiple partners, MSM • Unprotected sex involving exchange of body fluids • Injection drug abuse • Blood product receipt (before reliable screening introduced) • In countries with generalized epidemics (e.g. South Africa), screening for HIV should be part of routine primary care

8. Risk Assessment • Testing should be recommended for all pregnant women as soon as pregnancy is detected • Women with high risk for HIV infection, should have a repeat test during the third trimester • During labor, all women with unknown serologic status for HIV should be tested with the use of rapid tests • All exposed new born children should be tested between within 48 hours, 1 -2 months and 3-6 months.

9. Anonymous vs Confidential • Anonymous • Identifying information not provided • Results not linked to identifying information • Allows reporting of HIV infection without breaching confidentiality • Disadvantage: may not be able to locate clients for test results • Confidential • Clients linked to test result by identifying information • Results remain confidential • Informed consent

10. Pre-Test Counseling • Goal: reduce HIV acquisition and transmission • Accurate and current information about HIV • Obtain informed consent • Transmission and acquisition • HIV test info: risk, benefits, meaning of potential test results • Assessment of individuals risks and appropriate risk reduction activities • Capacity to comprehend HIV testing and consent

11. Post-Test Counseling • Accurate and current information about HIV • Local resources • Risk reduction education • Referrals for ongoing care and support • Healthy living strategies • Meaning of test results and state reporting guidelines • Mental health support / counseling

12. Patient centered counseling • Talk with rather then to the patient • Individualize sessions (patients needs) • Neutral non-judgmental • Use open ended questions • Aim for a realistic risk-reduction plan • Offer options not directives • Recognize the counselor's limited role.

13. Diagnosis of HIV Infection • Viral antibodies • Viral antigens • Viral RNA/DNA • Culture Lancet, 1996; 348: 176.

14. Sensibility & Specificity Sensibility: Ability to identify infection in individuals that are truly infected. Specificity: Ability of the test to identify as negative individuals that are NOT infected

15. HIV Diagnostics • Approximate times to positivity* • 1st generation ELISA 42 days • 3rd generation ELISA 23 days • p24 antigen assays 16 days • RNA PCR 11 days • 95% seroconvert by 6 months • False positives • autoimmune disease, renal failure, cystic fibrosis, multiple pregnancies/transfusions, liver disease, post immunization • False negatives • window period, agammaglobulinemia, Group O, N, ± HIV-2 *Busch et al., Transfusion 1995;35:91-97

16. Negative Antibody Test Results • HIV negative • Recent infection: too early for seroconversion • CDC: follow-up testing at 6 weeks, 12 weeks, 6 months

17. Confirmation Process • Non-negative screenings should be confirmed • Western Blot (WB) • Immunofluorescent Antibody Assay (IFA) • Higher specificity than EIA • Interpretation can be subjective

18. IFA (Immunofluorescent Antibody Assay • Fluorognost HIV-1 IFA uses human material from infected T cells that express HIV-1 antigens. The cells are fixed to the surface of a glass slide, non infected cells are used as controls. When HIV antibodies are present in serum or plasma they attach to the infected cells but not to the non-infected cells. • Uses microscope, faster results

19. Western Blot • Detects antibodies to HIV-1 proteins • Core: p17, p24, p55 • Polymerase: p31, p51, p66 • Envelope: gp41, gp120, gp160 • Negative: no bands • Positive: • Reactivity to gp41 + gp120/160 or • Reactivity to p24+gp120/160 • Indeterminate: • EIA repeatedly reactive • Presence of any band pattern not meeting criteria for positive results

20. Predictive Value: HIV Ab Tests • Importance of pre-test probability in determining false + rate (Bayes theorem) • Depends on the prevalence of HIV infection in the population • Low HIV prevalence: predictive value of a positive test is low • HIV Ab testing of low prevalence populations likely to produce more false-positive than true-positive results

21. False Positive Results in Low vs. High Prevalence of HIV infection

22. Window Period • Time delay from infection to positive EIA • Average: 10-22 days • Most seroconvert within six months Am J Med 2000; 109

23. False Negative Results • High-prevalence population: 0.3% • Low-prevalence: <0.001% • Usually due to testing during window period • Rare patients seroconvert in late-stage disease • Technical or clerical error • Type N or O • HIV-2

24. False Positive Test Results • Much less common than in earlier times • Frequency: 0.0004% to 0.0007% • Causes • Autoantibodies (single case, Lupus, ESRD) • HIV vaccines • EIA+: 68% • WB+: 0-44% • Technical / clerical error NEJM 1988;319:961 Ann Intern Med 1989;110:617

25. Indeterminate Results • 4-20% of WB assays with positive bands • Testing during seroconversion • p24 usually appears first • Late stage HIV: loss of core antibody • HIV vaccine recipients • Technical / clerical error • Infection with O strain or HIV-2

26. Indeterminate Results (continued) • Cross-reacting nonspecific antibodies • Collagen-vascular disease • Autoimmune disease • Pregnancy • Organ transplantation • Lymphoma, other malignancies • Liver disease • Multiple sclerosis • Recent immunization

27. Indeterminate Results • Evaluate HIV risk • Low risk: almost never infected with HIV-1 or HIV-2 • Repeat testing: often continued indeterminate • Cause: frequently not established • HIV unlikely • Follow-up serology in 3 months • Seroconversion: usually WB+ in 1 month • Repeat testing at 1, 2, 6 months • Counseling to reduce potential transmission

28. Frequency of HIV Testing • High risk behavior: every 6-12 months • Annual seroconversion • General population: 0.02% • Military recruits: 0.04% • MSM: 0.5 - 2% • IDU in high prevalence area: 0.7-6%

29. Alternative Testing • Rapid Testing • Alternative body fluids • Saliva • Urine • Vaginal secretions • Viral detection • Home test kits

30. Rapid HIV Antibody Detection • Results in 15-20 minutes • Occupational exposure • Women in labor with unknown HIV status • Clients unlikely to return for visits • Outreach • ERs

31. Rapid HIV Antibody Detection • OraQuick HIV-1 Antibody Test (OraSure) • Results read by provider in 20 minutes • Sensitivity: 99.6% / Specificity: 100% • $20-30 • Fingerstick sample of blood • Negative test: definitive • Positive test: needs standard serology confirmation • Not recommended for HIV-2 screening

32. OraQuick Advance HIV-1/2 • CLIA (Clinical Laboratory Improvement Amendment) waived for whole blood, saliva, plasma • Room temperature • Detects VIH-1/2 • Results in 20 minutes

33. HIV 1/2

35. Rapid Test Results • Reactive (preliminary positive) rapid test • Screening test is positive • Preliminary result • Confirmatory testing required • Precautions to avoid viral transmission • Negative rapid test • No recent exposure: definitive negative • Possible recent exposure: • Recommend re-test • Counseling to prevent transmission

36. P24 Antigen • Part of blood bank algorithms since 1996 • Uncommon in clinical practice • Detects free, non-complex HIV antigens in peripheral blood

37. Indications for HIV Viral Detection • Confusing / indeterminate serologic test results • Acute retroviral infection • Neonatal infection • Window period following exposure • Not FDA approved for diagnosis of HIV • Expensive

38. Viral Detection • p24 Antigen • HIV-1 DNA PCR • Most sensitive: able to detect 1-10 copies of proviral DNA • S/S: 99% / 98% • HIV-1 RNA (RT-PCR, bDNA) • S/S: 95-98% • Viral culture of PBMC: expensive, labor intensive, reliability variable

39. National RecommendationsFor HIV Testing ofPregnant Women • Recommendations for HIV Screening of Pregnant Women Universal testing for all pregnant women as a routine part of prenatal care using an “opt out” approach • Labor and Delivery: routine rapid testing if HIV status unknown • Postnatal: rapid testing for all infants whose mother’s status is unknown • Regulations, laws, and policies about HIV screening of pregnant women vary from state to state

40. Diagnosis in Children < 18 months

41. DNA PCR DNA PCR (detects HIV proviral DNA within PBMC) Qualitative • Reactive • Non Reactive Sensitivity increases from 38% at birth to93% at 14 days at one mont S-S between 90-100% (Dunn 1995)

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43. Detuned Antibody Testing • Less sensitive ELISA test • May help distinguish between recent seroconverters and those with long-standing HIV infection • Current ELISAs can detect relatively low levels of Ab • HIV Ab levels increase over first few months • Recent infection: standard ELISA positive • Detuned assay: negative • Able to diagnose individuals who have already seroconverted on a standard ELISA but are still early in infection

44. Recommended Websites • AIDSInfo website (www.aidsinfo.nih.gov) • AETC National Resource Center • http://www.aidset.org • http://www.cdc.gov/spanish/enfermedades.htm • http://www.womenchildrenhiv.org/ • www.aahivm.org

45. “If we begin with certainties, we shall end in doubts; but if we begin with doubts, and are patient with them, we shall end with certainties” Sir Francis Bacon