Screening in Medicine Flashcards
What are the two questions patients should always ask their physician when a medical screening test is recommended?
1) How accurate is the test you are recommending? (Sensitivity and specificity)
2) How confident are you with the test results of wether i do or do not have dz? (PPV or NPV)
True positive (TP)
Test correctly reports a ______ result in a patient that ____ have the dz.
It belongs in what box?
Positive; DOES have the dz
Box A
True Negative (TN)
Test correctly reports a _______ result in a pt that ______have the dz.
What box?
Negative; DOES NOT
Box D
False Positive (FP)
Test INCORRECTLY reports a _______ result in a pt that ______have the dz.
What box?
Positive; DOES NOT
Box B
False Negative (FN)
Test INCORRECTLY reports a _______ result in a pt that ______have the dz.
What box?
Negative; DOES
Box C
What are the two measurements that describes the accuracy of TEST RESULT based on known dz status?
Sensitivity and specificity
- we know the outcome
- just dealing with the test, not the ppl
- % in correctness of answer that I already know
- Box A is the numerator for sensitivity
- Box D is the numerator for specificity
1) Sensitivity is the percentage of time that a TEST is ____ in a patient that is _____ to have the dz.
2) What is the formula?
3) A highly sensitive test has a low _____ rate.
1) positive; known
- how accurately a test can correctly detect presence of dz when in face dz is actually known to be present
2) TP/(All dz’ed) x 100%
- A/(A+C)
- TP/ (TP + FN)
3) False negative
(want it to be 100% sensitive so 0% FN’s
1) Specificity is the percentage of time that a TEST is ____ in a patient that is _____ to have the dz.
2) What is the formula?
3) A highly specific test has a low _____ rate.
1) Negative; known NOT to have the dz
- how accurately a test can correctly detect absence of dz when in face the dz is KNOWN TO BE ABSENT
- negativity-of-test in the healthy (% of time that TN are found)
2) TN/(All non-dz’ed) x 100% - D/(B+D)
- TN/(FP+TN)
3) False positive rate
What two tests predict accuracy of DX based on KNOWN test result?
Positive predictive value (PPV)
Negative predictive vaule (NPV)
- predicitng a dx, treating patients, and talking to patients about their result
- answer to question 2
Positive predicitve value (PPV)
1) How accurately a ____ test correctly predicts the ____ of dz.
2) Percentage of _____ in patients with a ____ test. (correct prediction)
3) What is the calculation?
4) A test with a high PPV has a low _____ rate.
1) positive; presence of dz
2) True Positives; positive
3) PPV = TP/(All positive tests) x 100%
- A/(A+B)
- TP/(TP+FP)
4) low FP rate
Negative predicitve value (NPV)
1) How accurately a ____ test correctly predicts the ____ of dz.
2) Percentage of _____ in patients with a ____ test. (correct prediction)
3) What is the calculation?
4) A test with a high NPV has a low _____ rate.
1) Negative; absence of dz
2) True Negatives; negative
3) NPV = TN / (All negative tests) x 100%
- D/(C+D)
- TN/ (FN+TN)
4) False negative
Prevalence affects _____ but not ______.
PPV or NPV, but not sensitivity or specificity
What describes the percentage of all correctly-ID patients (TPs and TNs, collectively) out of the total (all) number of screened patients?
What is the formula?
Diagnostic accuracy - DA
DA = (TP + TN) / (All patients) x 100%
- (A+D)/(A+B+C+D)
1) Likelihood ratios is the ratio of 2 _______.
2) Its the ratio of percentage of given test result (positive or negative) for a person _____ dz divided by % of the same test result (+ or -) for a person ____ dz.
1) 2 probabilities/percentages
2) with; without
Likelihood ratio positive (LR+)
1) Percentage of a _____ test in the ___ of dz divided by the percentage of a ____ test in the ____ of dz.
2) Formula
3) Should LR+ be very high or very low?
1) positive; presence / postivie; absence
2) LR+ = (A/(A+C) / (B/(B+D)
- Sensitivity / (1-Specificity)
3) very high
want it to be greater than 10
