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HIV Testing

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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 ... – PowerPoint PPT presentation

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Title: HIV Testing


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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