HIV Testing

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HIV Testing
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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

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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

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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

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Consequences of a False Positive

• Life goes on hold
• Depression/Suicide
• Family and emotional issues
• Others

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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

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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

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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.

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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.

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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

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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

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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.

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Problems

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

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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.

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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.

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Other Tests of Importance
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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.

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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

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Saliva Tests

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

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Urine tests

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

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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???)

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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

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Anonymous vs. Confidential Testing

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

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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

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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.