HIV Serology Flashcards
HIV Epidemiology and Testing Accuracy Frequencies
(As per CDC National HIV Surveillance System) Between 2006 and 2009, estimated 125,104 new cases of HIV infection
- 49% diagnosed on first test
- 59% diagnosed within 1-2 years after initial negative test
HIV Window Period
(duration, testing during that time)
Duration: 2-6 weeks
Testing:
- Older testing methods were not sensitive enought to detect window Ab, so many cases went undiagnosed
- Currently, two tests exist:
- circulating p24 antigen
- viral DNA/RNA
- not typically performed for individual testing due to cost
- Red Cross does it for bulk bld screening
HIV Screening Guidelines
(3 groups)
- CDC - 2006
- Voluntary HIV screening of all patients 13-64 years without written consent or counseling
- Verbal concent required
- American College of Physicians (ACP) – 2009
- Universal screening up to 75 years
- USPTF – 2013
- Universal HIV screening for ages 15-65 years
HIV Screening Guidlines, by Individual
(2 tiers, 1/5 specifics per tier))
- One time testing at medical clinic visit
- low risk pts
- Annual/frequent testing
- IV drug users
- men sexually active c men
- persons who exchange money for sex
- sex partners of…
- HIV infected persons
- bisexual individuals
- IV drug users
- people c unknown HIV status
- pregnant women, even if screened in earlier pregnancies
CDC HIV Test Reccomendations
(2 old, 2 new)
Old, no longer recommended:
- Screening - ELISA test
- Confirmation - Western blot
Current recommendations: combination testing
- p24 antigen (will appear first)
- HIV antibodies
Modes, Current HIV Tests
(
- Rapid Ab testing
- 99% sensitivity and specificity
- Must be confirmed c Ag/Ab test
- Availible OTC, eval saliva (Planed Parenthood used to use these)
- Combination HIV Ag/Ab tests
- Most sensitive and accurate
- First confirmatory test
- HIV1/HIV2 differentiation assay
- Performed if combination test is positive
HIV Type-Specific Prevalence
HIV1 - Dominant HIV in USA
HIV2 - Dominant HIV in 3rd world countries
Current Untestable Period, Ab/Ag testing
15-20 days
Currently in 4th generation of enzyme-linked immunoassay testing
HIV Diagnostic Testing Algorhythm
NYS follows this federal algorhythm, too
Home-Based HIV Testing
(2 types c general facts for each, indication)
Indication: individuals unlikely to seek medical care (these are availible OTC)
Tests:
- OraQuick In Home HIV Test
- MOA - detect HIV1/HIV2 ab in saliva
- Positive results must be confirmed (Ab/Ag test, Viral DNA/RNA tests)
- May be negative during window period
- Home Access HIV 1 Collection Test System
- MOA - evaluate finger prick bld
- Screening enzyme immune assay
- Confirmatory immunofluorescent Ab
- Bld taken at home then mailed to lab for testing
- 100% estimated sensitivity and specificity
- MOA - evaluate finger prick bld
Viral Detection
*“Alternate approach” to HIV testing, usually due to cost *
- Viral components are present before HIV ab’s are detected
- Most commonly used methods detect
- HIV RNA
- HIV p24 Ag
HIV RNA
(sensitivity, FDA status, uses)
Sensitivity: lower than immunoassays for established HIV1 infection
FDA: only approves HSV1 testing
Uses: Primarily for screening and monitoring disease
- Blood donors – screening
- Management of HIV infected patient - monitoring
HIV p24 Ag
(sensitivity, detectable time range)
Less expensive than HIV RNA
Detectability: ~1-2 weeks post viral transmission
Sensitivity: 89%
ELISA Testing
- Enzyme Linked Immunoabsorbent Assay
- Tests for antibodies to HIV
- High sensitivity
- Designed to detect all infected individuals
- Because it does not detect antigens, this test cannot detect infection in its earliest stages
Western Blot Test
- Gold standard for validating positive ELISA test (OLD PROTOCOLS)
- Detects presence of antibodies to HIV virus in patient
- Electrophoresis that separates lab grown HIV antigens
- p24, gp41, gp120/160
