POC Infectious diseases + Stats Flashcards
(31 cards)
What is measured in HIV tests? (3)
HIV antigens
HIV RNA
Antibodies
What do POC rapid HIV test for?
Antibodies
- indicator of body’s response to the virus
Why do we use POC HIV testing in labour/delivery?
It is possible to reduce HIV transmission to the infant if HIV status is known
- provide more rapid results than lab tests and possibly more accurate than ELISA (more expensive though)
What are types of POC HIV tests available?
- Lateral flow tests (similar to pregnancy, RATs)
- Flow-through tests
What is the INSTI test?
Detects?
What kind of test?
What does it use from your body?
HIV test
Flow through test
Detects presence of HIV-1/HIV-2 antibodies
- uses blood (at home), serum or plasma
What are the steps of a flow-through test?
- Analyte capture molecules: HIV antigens
- Located at the bottom of the test (to capture) - Specimen: usually blood
- Diluted in specific solution –> flows through membrane toward capture molecule - Analyte molecules: HIV antibodies
- If present, will bind to capture molecules (HIV antigens) - Detection molecules: specific solution, added last
- If antibodies bind to antigens, detection molecules will bind captured analyte and allow visual detection (dot)
What do tests for strep throat (pharyngitis) test for?
What kind of assay?
Group A streptococcus
Lateral flow assays
What symptoms can indicated bacterial pharyngitis rather than viral? Need to confirm?
- Under 14
- Enlarged, tender lymph nodes
- Fever
- Absence of cough
Confirm with microbial testing + throat culture
Are pharyngitis rapid antigen detection better at ruling in or ruling out strep throat
Better at ruling in
- high specificity (SPIN)
What do the following tests test for COVID-19?
PCR
Rapid antigen
Serological tests
PCR
- Viral RNA
Rapid antigen
- Viral antigens
Serological tests
- Measure antibodies to show past infection
When will the tests start to work?
PCR
Rapid antigen
Serological tests
PCR
- can detect sooner
- BUT can stay positive after no longer infectious
Rapid antigen
- Can produce FALSE NEGATIVES early on
Serological tests
- used detect host response to injection a week after symptoms
How to improve sensitivity in COVID tests
- swab both cheeks, back of tongue or throat, then both nostrils
- no food/drink/smoking/meds 30 minutes before test
What are reasons for false positives for COVID-tests?
- Acidic foods/bev
- Not using buffer, using water drinks
- Leaving test too long
- Lot-specific devices
Define sensitivity
Probability of getting a POSITIVE result WITH disease
Define specificity
Probability of getting a NEGATIVE result WITHOUT disease
Define false positive. Equation?
Getting an incorrect positive result WITHOUT the disease
1-specificity
Define false negative. Equation?
Getting an incorrect negative result WITH disease
1-sensitivity
Define positive predictive value
Probability of actually HAVING the disease AMONG people with a POSITIVE test
Define negative predictive value
Probability of NOT having the disease AMONG people with a NEGATIVE test
Low sensitivity leads to..
high false negative/positive rates?
high False negative
Low specificity leads to..
high false negative/positive rates?
high false positive
What do positive and negative predictive value highly dependant on?
Prevalence of the disease
Positive predictive value
- HIGHER with high prevalence
Negative predictive value
- LOWER with high prevalence
Define likelihood ratio
The probability of a particular test result for a person WITH disease
divided by
WITHOUT disease
Define likelihood ratio for a positive test result.
Equation for LR+
How is it expressed as?
The probability of a positive test result for a person WITH disease
divided by
positive WITHOUT disease
Equation: Sensitivity/(1-specificity)
OR
True positive rate/false positive rate
Expressed as a decimal
