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HIV Testing

HIV Testing. Enzyme Linked Immunosorbent Assay ELISA. First real test to detect HIV (1983) Was developed 4 years after the first cases of AIDS Initially designed to screen blood supply First month of testing, 1% of blood supply was HIV positive, Retesting, 17% Confirmatory test, 4%

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HIV Testing

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  1. HIV Testing

  2. Enzyme Linked Immunosorbent AssayELISA • First real test to detect HIV (1983) • Was developed 4 years after the first cases of AIDS • Initially designed to screen blood supply • First month of testing, 1% of blood supply was HIV positive, • Retesting, 17% • Confirmatory test, 4% • Is cheap $8 in state labs, $60-75 in private labs • Is a positive predictive value test • Designed to be very sensitive • Result, gets more false positives • 90% accuracy rate

  3. How it Works • Virus protein is first attached to a lab dish • Serum sample is prepared from the patients blood • Is placed in the dish containing bound HIV viral proteins. • If HIV antibodies are in the serum, they will bind to the dish with HIV proteins • Remove serum and wash dish • Apply a stain that detects antibodies • If positive, dish is stained • If negative, dish is not stained • Is now automated

  4. False Positives • Fewer than 1% of results are false positives • 1/1000 = 10/10,000 = 100/100,000 • Say positive when you are not • Can be devastating • Is one argument against mass screening • Cost as well • 2,800,000/280 million US citizens • Why • Had several children • Rheumatological diseases • Malaria • Alcoholic Hepatitis • Others • Consequence • Develop another test

  5. Consequences of a False Positive • Life goes on hold • Depression/Suicide • Family and emotional issues • Others

  6. False Negatives • Fewer than 1% of results say you are negative when you are actually infected with HIV • 1/1000 = 10/10,000 = 100/100,000 • 280,000/280 million people • Many reasons for false negatives • Window period • Some people do not develop a immune response to the virus • Are rare • Still spread the virus

  7. Other Issues • Some people who are exposed to HIV may have a successful immune response and completely eliminate the virus • VERY VERY Rare • Most people who are exposed remain infected

  8. Western Blot • Is a confirmatory test • Also tests for HIV antibodies • Has a lower level of false positives than ELISA • Usually used when a ELISA test has a positive hit • Today, use the combination. If positive in both, then the sample is considered positive. • 99% positive for results when used together.

  9. How it Works • Uses Gel electrophoresis • HIV is cultured in Human leukemia cells • Cells are broken open • Proteins are placed on a gel that receives an electrical charge • Viral proteins are separated and settle out at different levels • Proteins at different levels are blotted onto strips of nitrocellulose paper • Serum is placed on the paper • If antibodies are present, they bind to the proteins • Strip is washed • Add a enzyme and color agent • If HIV is present, a color reaction will occur at the site of the HIV protein.

  10. Problems • Lack of standardization between NIH, ARC, DuPont, DOD, and other organizations • No real agreement about what constitutes a positive test • Takes longer to run (12-24 hours) • Is more labor intensive • Result – Costs more to run

  11. Viral Load Test • p24 antigen test (1995) • Measures the major core protein of HIV (p24) • Detects the protein by using an antibody against it. • Can detect as early as 16 days after infection • Past - Done when full-blown AIDS developed • Today – Mandatory use at blood and plasma centers

  12. Nucleic Acid Testing NAT • 1999 • Used to test for HIV-1, and Hepatitis B and Hepatitis C in blood centers • Use molecular techniques • Generally tests for viral nucleic acids • Does not indirectly test for antibodies • Has closed the window to 10 days for detection.

  13. Problems • Is expensive ($80 minimum) • Requires specially trained lab technicians • Takes 12 hours • Still have a 1% chance for a false negative

  14. Polymerase Chain ReactionPCR • Indirectly can measure viral load • Takes any DNA fragment from a single cell • Is exponentially multiplied to an amount large enough to be measured. • Does not require antibody formation • Very sensitive • Six molecules/150,000 cells • One molecule in 10 micro liters of blood • Can be used to detect HIV in people who are suspected of having the virus but test negative by other techniques.

  15. Serologic Testing Algorithm for Recent HIV Seroconversions (STARHS) • Uses two different ELISA tests to determine if a person was recently infected or has had HIV for a period of time (6 Months) • Test 1 • Very Sensitive. Detects small numbers of antibodies • Test 2 • Is less sensitive but picks up large antibodies that appear 3-5 months after infection.

  16. Other Tests of Importance

  17. Rapid Tests • Single Use Diagnosis System (SUDS) • Use reagents to bind to HIV antibodies in Serum • Has a 99.9% accuracy rate • Is comparable to the newer ELISA tests • Good where people do not return for results.

  18. Other Rapid Tests • HEMA - Strip • SERO – Strip • Are used in over 20 countries • Require no additional equipment • Blood or serum is paced at the tip of a strip and allowed to diffuse along it. • Strip has reagents that react to antibodies • Can be done in 10 minutes • Also has a built in quality control

  19. Saliva Tests • Example OraSure • Are easier • Less expensive • Noninvasive • May be slightly less accurate • Also has a home version under trials

  20. Urine tests • Sentinel • Has same advantages as saliva tests • Is less sensitive than blood tests • Testing is done by professional laborites

  21. Home Testing • Example Home Access Express-HIV Test • Take a blood sample at home with finger stick • Mail it to a lab • Call in for results • Advantage • Cost • Most people are the worried well (May be changing) • Disadvantage • What happens if positive • May need face to face counseling (Hotlines???)

  22. Who Should Be Tested? • Persons who engage in high-risk behaviors • Anal sex • IDU • Have sex with people in high-risk groups • Have certain medical symptoms or conditions • Become Pregnant • Had a blood transfusion before 1985 • If positive for other STD

  23. Anonymous vs. Confidential Testing • When testing began was a big debate • Anonymous was a big mistake • Now, most states require confidential testing only (Idaho)

  24. Conclusions and the Future • Have come a long way • Currently have good and reliable tests • Will get better • Cost needs to get lower • Need fast tests that are cheap • Are being done by insurance companies • Implications are huge for health care and life insurance companies

  25. Testing is Not the Answer • It only tells you if you are positive or negative • Only does so if there is enough virus to detect • At this time Prevention is the only answer • In the future, a vaccine or evolution will be the solution to HIV • Problem: With new strains and multiple mutations, does not appear close at this time.

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