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Routine HIV Screening in Health Care Settings

Routine HIV Screening in Health Care Settings. HIV Diagnostic Testing. David Spach, MD Clinical Director Northwest AIDS Education and Training Center Professor of Medicine, Division of Infectious Diseases University of Washington Seattle.

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Routine HIV Screening in Health Care Settings

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  1. Routine HIV Screening in Health Care Settings HIVDiagnostic Testing David Spach, MDClinical DirectorNorthwest AIDS Education and Training CenterProfessor of Medicine, Division of Infectious DiseasesUniversity of Washington Seattle This project was funded under cooperative agreement number U65/PS000821from the Centers for Disease Control and Prevention (CDC). 

  2. HIV Diagnostic Testing • Types of HIV Diagnostic Tests • Initial and Supplemental HIV Tests • Sensitivity and Specificity of HIV Tests • Laboratory-Based HIV Testing Algorithms • Point-of-Contact (Rapid) HIV Testing Algorithms • Diagnosis of Acute HIV

  3. HIV Diagnostic Testing • Types of HIV Diagnostic Tests • Initial and Supplemental HIV Tests • Sensitivity and Specificity of HIV Tests • Laboratory-Based HIV Testing Algorithms • Point-of-Contact (Rapid) HIV Testing Algorithms • Diagnosis of Acute HIV

  4. Types of HIV Diagnostic Tests HIV Antibodies HIV-1 RNA HIV p24 Antigen Most Common Test for Established Infection Used for Acute HIV and Indeterminate WB Rarely UsedFuture use: 4th Generation EIA

  5. HIV Diagnostic Testing • Types of HIV Diagnostic Tests • Initial and Supplemental HIV Tests • Sensitivity and Specificity of HIV Tests • Laboratory-Based HIV Testing Algorithms • Point-of-Contact (Rapid) HIV Testing Algorithms • Diagnosis of Acute HIV

  6. Initial and Supplemental HIV Tests • Initial Test - Enzyme Immunoassay (EIA) - Chemiluminescent Immunoassay (CIA) • Supplemental Tests - Western blot - Indirect Immunofluorescence Assay (IFA) - Qualitative HIV-1 RNA

  7. Initial and Supplemental HIV Tests • Initial Test - Enzyme Immunoassay (EIA) - Chemiluminescent Immunoassay (CIA) • Supplemental Tests - Western blot - Indirect Immunofluorescence Assay (IFA) - Qualitative HIV-1 RNA

  8. Generation of EIA Tests First Second Third *Fourth *Not US FDA-approved as of 10/1/09 Uses crude viral lysate Uses recombinant HIV antigens or peptides Detects IgM and IgG in “Sandwich” EIA Detects HIV antibodies and p24 antigen

  9. Traditional HIV EIAs 96-Well Microtiter Plate EIA Interpretation of EIAs • Based on color change/fluorescence • Change compared with standardized cut-off • Result positive or negative • No specific antibody reaction information • Multiple samples run with traditional EIA

  10. HIV-1 Western Blot Antigens p = protein gp = glycoprotein Number = molecular weight

  11. Components Used in HIV-1 Western Blot HIV Western blot Strip Color Reagent Enzyme Detector Y Y Y Antihuman IgG Antibodies Y Y Y Y Y Y Human HIV Antibodies (from patient serum) HIV Antigens (on Western blot)

  12. Sample HIV-1 Western Blot Color Reagent Enzyme Detector Y Anti-human IgG Y Y Y Antibodies to gp120 Y Y HIV gp120 antigen Color Reagent Enzyme Detector Y Y Anti-human IgG Y Y Y Y Antibodies to p24 HIV p24 antigen Test Completed gp120 & p24 bands Visible

  13. HIV-1 Gene Products & Western Blot

  14. HIV-1 and HIV-2 Gene Products & Western Blot

  15. Interpretive Criteria for HIV-1 Western Blot Positive Control Source: CDC. MMWR. 1989:38(S-7):1-7.

  16. Interpretive Criteria for HIV-1 Western Blot Negative No bands: Source: CDC. MMWR. 1989:38(S-7):1-7.

  17. Interpretive Criteria for HIV-1 Western Blot Positive At least two of the following bands:p24gp41gp120/160 Source: CDC. MMWR. 1989:38(S-7):1-7.

  18. Interpretive Criteria for HIV-1 Western Blot Examples Indeterminate One or more bands presentNot meeting positive criteria Most common bands seen withindeterminate Western blot (IWB)p17, p24, p55 Source: CDC. MMWR. 1989:38(S-7):1-7.

  19. HIV Diagnostic Testing • Types of HIV Diagnostic Tests • Initial and Supplemental HIV Tests • Sensitivity and Specificity of HIV Tests • Laboratory-Based HIV Testing Algorithms • Point-of-Contact (Rapid) HIV Testing Algorithms • Diagnosis of Acute HIV

  20. HIV Antibody Test: Sensitivity Sensitivity Probability that test is positive if person is infected

  21. HIV Antibody Test: Sensitivity Persons Infected with HIV: n = 50 Example

  22. HIV Antibody Test: Sensitivity Persons Infected with HIV: n = 50 HIV Antibody Testing: 49/50 Positive Example

  23. HIV Antibody Test: Sensitivity Persons Infected with HIV: n = 50 HIV Antibody Testing: 49/50 Positive Sensitivity = 49/50 = 98% Example

  24. Sensitivity of HIV Antibody Tests Used in US HIV Antibody TestsSensitivity >> 99%

  25. HIV Antibody Test: False Negative HIV-Infected Persons HIV Antibody Testing Example

  26. HIV Antibody Test: False Negative HIV-Infected Persons HIV Antibody Testing False Negative Example

  27. Some Causes of False-Negative Antibody Tests • Acute HIV Infection • Advanced HIV Infection • Antiretroviral Therapy

  28. HIV Antibody Test: Specificity SpecificityProbability that test is negative if person is not infected

  29. HIV Antibody Test: Specificity Persons NOT Infected with HIV: n = 50 Example

  30. HIV Antibody Test: Specificity Persons NOT Infected with HIV: n = 50 HIV Antibody Testing: 48/50 Negative Example

  31. HIV Antibody Test: Specificity Persons NOT Infected with HIV: n = 50 HIV Antibody Testing: 48/50 Negative Specificity = 48/50 = 96% Example

  32. HIV Antibody Test: False Positive Persons NOT Infected with HIV HIV Antibody Testing Example

  33. HIV Antibody Test: False Positive Persons NOT Infected with HIV HIV Antibody Testing False Positive Example

  34. Specificity of HIV Antibody Tests Used in US Initial HIV Antibody TestsSpecificity > 98% Supplemental HIV Test (if initial test positive)Specificity >> 99%

  35. HIV Antibody Test: Specificity True Infection False Positive False Positives: proportion of false-positive tests increases in populations with low HIV prevalence

  36. Causes of False-Positive HIV Antibody Tests • Other Viral Diseases • Hematologic Disorders • Liver Disease • Immunizations • Autoimmune Disorders

  37. Interpreting Test Results Sensitivity:Probability test = positive IF person = positive Specificity:Probability test = negative IF person = negative Positive Predictive Value:Probability person = positive IF test = positive Negative Predictive Value:Probability person = negative IF test = negative

  38. Positive Predictive Value of HIV Tests in Populations with Differing HIV Prevalence Example: HIV Testing 1,000 Persons

  39. HIV Diagnostic Testing • Types of HIV Diagnostic Tests • Initial and Supplemental HIV Tests • Sensitivity and Specificity of HIV Tests • Laboratory-Based HIV Testing Algorithms • Point-of-Contact (Rapid) HIV Testing Algorithms • Diagnosis of Acute HIV

  40. General Approach to HIV Diagnostic Testing Initial Supplemental Optimized for Sensitivity Optimized for Specificity

  41. 1989 CDC/ASTPHLD HIV Testing Algorithm Initial Supplemental EIA Western blotorIFA Repeatedly Reactive Source: CDC. MMWR. 1989;38(S-7):1-7.

  42. Modern HIV Testing Algorithms Initial Point-of-Contact Approach to HIV Testing Laboratory-Based Approach to HIV Testing Diagnosing Acute HIV Source: CDC. MMWR. 2001;50(RR19):1-58.

  43. HIV Testing Algorithms http://www.aphl.org/aphlprograms/infectious/hiv/Pages/HIVStatusReport.aspx

  44. HIV Testing Algorithms http://www.aphl.org/aphlprograms/infectious/hiv/Pages/HIVStatusReport.aspx

  45. Laboratory-Based HIV Testing Algorithms Initial HIV-1/HIV-2Immunoassay* Nonreactive HIV Negative *Enzyme Immunoassay (EIA) or Chemiluminescent Immunoassay (CIA)

  46. Laboratory-Based HIV Testing Algorithms Initial Repeat Testing (in duplicate) HIV-1/HIV-2Immunoassay* Reactive *Enzyme Immunoassay (EIA) or Chemiluminescent Immunoassay (CIA)

  47. Laboratory-Based HIV Testing Algorithms Initial Repeat Testing (in duplicate) HIV-1/HIV-2Immunoassay* Reactive Both Nonreactive HIV Negative *Enzyme Immunoassay (EIA) or Chemiluminescent Immunoassay (CIA)

  48. Laboratory-Based HIV Testing Algorithms Initial Supplemental HIV-1 Western blotorHIV-1 IFAor HIV-1 RNA HIV-1/HIV-2Immunoassay* Repeat Testing (in duplicate) Reactive Repeatedly Reactive *Enzyme Immunoassay (EIA) or Chemiluminescent Immunoassay (CIA)

  49. Laboratory-Based HIV Testing Algorithms Initial Supplemental HIV-1 Western blotorHIV-1 IFAor HIV-1 RNA HIV-1/HIV-2Immunoassay* Repeat Testing (in duplicate) Reactive Repeatedly Reactive Negative HIV Negative *Enzyme Immunoassay (EIA) or Chemiluminescent Immunoassay (CIA)

  50. Laboratory-Based HIV Testing Algorithms • Test for HIV-2 with any of Following: • Indicated by local HIV-2 prevalence • Indicated by travel or risk history • Indicated by clinical presentation Initial Supplemental HIV-1 Western blotorHIV-1 IFAor HIV-1 RNA HIV-1/HIV-2Immunoassay* Repeat Testing (in duplicate) Reactive Repeatedly Reactive Negative HIV Negative *Enzyme Immunoassay (EIA) or Chemiluminescent Immunoassay (CIA)

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