HIV Flashcards
what is the sensitivity of HIV screening tests?
high sensitivity (>98%)
What do HIV screening tests usually detect?
- antibodies to HIV-1 and HIV-2
4th gen - also detects - HIV-1 p24 antigen
Seological tests for HIV are usually based on what laboratory assay?
Serological tests - usually use
enzyme immuno assays (EIA)
4th generation (antibody and antigen) tests - more sensitive than antibody only tests
Why are 4th generation HIV tests recommended?
4th generation = antibody and antigen tests,
More sensitive than antibody only tests
Better in detecting or excluding HIV when a recent exposure has occurred (<4-6 weeks).
In what situation may there be a false negative HIV test?
A test can be falsely negative very early in the window period
e.g. If a high risk HIV exposure occurred in the previous 4-6 weeks s
A negative test with a 4th generation (antigen + antibody test) EIA at 4 weeks excludes HIV infection with a high degree of certainty.
(a few cases described of prolonged seroconversion, usually with simultaneous other viral illness)
What confirmation is required of a positive HIV screening test?
Confirmation by second and third serological test
what is an equivocal or indeterminate HIV test?
An equivocal / indeterminate tests = a positive screening test which is negative when tested by a second and third serological test.
Causes of an equivocal or indeterminate HIV test
Usually caused by a false positive reaction
Could be an early seroconversion when the screening test is more sensitive than the confirmatory tests.
Management of an equivocal or indeterminate HIV test
Repeat the sample 1 wk later
Will identify seroconversion if the confirmation test(s) become positive and/or p24Ag or HIV viral load is detectable
Patient can be reassured of false positive reaction if the repeat blood, drawn at least 1 week later, is negative
What test can be used for HIV incidence testing
Antibody avidity testing
Can predict whether the infection occurred in the preceding 4-5 months.
(sensitivity + specificity of 96% and 97%)
What principle foes HIV Antibody avidity testing utilise?
The test exploits the principle that the initial antibodies bind less strongly (low avidity) to antigen compared to antibodies produced later as part of the evolving immune response.
Can predict whether the infection occurred in the preceding 4-5 months.
When can HIV seroconversion be diagnosed?
Seroconversion can be diagnosed when the 4th generation screening test is positive but a confirmatory (3rd generation) test is negative.
A p24Ag or viral load test needs to be positive.
Evolving line blot assays with additional bands developing on follow-up sampling can also be used.
Sensitivity of HIV tests?
HIV tests - incredibly sensitive
>98%
due to the high levels of HIV antibodies produced by an infected person
Specificity of HIV tests?
specificity >98%
When might salivary HIV diagnostic tests be useful?
for children / severe needle phobia
what is the correct storage of HIV samples
No refrigeration of samples is necessary unless stored for more than 1-2 days.
What proportion of new HIV diagnoses are MSM?
UK in 2015
MSM = 46% of new HIV diagnoses
What is a late HIV diagnosis?
For public health monitoring - late HIV diagnosis = CD4 cell count <350 within 3m of HIV diagnosis
Very late HIV diagnosis = CD4 count <200.
What is the significance of a late HIV diagnosis?
People diagnosed late are at increased risk of developing an AIDS-defining illness
+ have 10x increased risk of death in the year following their diagnosis
HIV prevention strategies
Condom use
PEPSE
Serosorting/stategic positioning - mixed data
PREP
Male circumcision - data from Africa suggests MC protects heterosexual men from acquiring HIV
Reduce the number of partners
What is the approximate rate of STS and HIV co-infection
Syphilis-HIV coinfection remains high
Up to 40% of cases of syphilis being in HIV infected MSM
How may being HIV +ve affect the presentation of STS
some minor differences syphiis presentation in HIV +ve patients include:
- primary syphilis- up to 70% present with >1 chancre + larger / deeper lesions
- 25% present with concomitant lesions of primary and secondary stages at presentation
- atypical and severe presentations of syphilis occur more frequently (still a v small minority)
- Syphilis can cause transient increase in the viral load and decrease in the CD4 cell count - resolve after treatment
Differences in managing STS in HIV +ve patients
- HIV patients are more likely to present with neurological syphilis in early syphilis
- HIV infection associated with increased risk of neurological complications in the short and long term
- consider treating all HIV patients with a neurosyphilis drug regimens given the high rates of positive CSF
Globally what proportion of people living with HIV are women?
Women >15 years = approximately 50% of global adults living with HIV
- The burden of disease in women is not evenly distributed worldwide