Diagnostic and Screening Tests Flashcards
(14 cards)
what is a diagnostic test?
established or rules out disease in individuals with abnormal signs/symptoms
What is a screening test?
establishes or rules out disease in individuals that appear healthy but may be at risk
When would you screen?
when dz is an important problem
natural history of dz presents a window of opportunity for early detection AND tx
cots of screening/dx/tx is favorably weighed against tx cost at usual time of diagnosis
suitable test avialable
What are the req’s for a suitable screening tests?
Accurate
acceptable to population
safe
inexpensive
able to ID cases that would benefit from early detection Tx
What are the 4 possible outcomes of any test?
True positive
True Neg
False pos
False neg
Define SENSITIVITY of a test
likelihood of a positive test among those witht the disease (TP)
“How good is the test at identifying people with the disease?”
decreases FALSE NEGATIVES
Define SPECIFICITY of a test
the likelihood of a negative test among those without the disease (TN)
“How good is the test at identifying individuals w/o the disease?”
Decreases FALSE POSITIVES
Write the equation for sensitivity:
TP / ( TP + FN )
A / ( A + C )
Write the equation for specificity:
TN / ( FP + TN )
D / ( B + D )
Describe the relationship between specificity and sensitivity?
Inverse relationship
define PVP:
Predictive Value Positive
if patient test positive, what is the probability they have the disease?
define PNV:
Predictive Value Negative
if the test is negative, what is the probability they are truly negative?
give the equation for PVP
PVP = A / A+B
give the equation for PVP:
PNP = D / C + D
