Diagnosis Flashcards
2013-18
A study was made of clinicians’ ability to diagnose infection on 149 patients coming to the emergency department with sore throats. (20) Doctors’ clinical impressions were compares to results of throat cultures for group streptococcus. Thirty-seven patients had positive throat cultures, and 27 of these were diagnosed by doctors as having strep throat. One hundred twelve patients had negative cultures, and doctors diagnosed 35 of those as having strep throat.
What is the sensitivity of the doctors’ clinical impression of strep throat in this study?
Sensitivity = 27/37 = 73%
Solution:
First, determine the numbers for each of the four cells: a=27; b-35; c=37-27 (or 10); d=112-35 (or 77)
2013-18
A study was made of clinicians’ ability to diagnose infection on 149 patients coming to the emergency department with sore throats. (20) Doctors’ clinical impressions were compares to results of throat cultures for group streptococcus. Thirty-seven patients had positive throat cultures, and 27 of these were diagnosed by doctors as having strep throat. One hundred twelve patients had negative cultures, and doctors diagnosed 35 of those as having strep throat.
What is the specificity?
Specificity = 77/112 = 69%
Solution:
First, determine the numbers for each of the four cells: a=27; b-35; c=37-27 (or 10); d=112-35 (or 77)
2013-18
A study was made of clinicians’ ability to diagnose infection on 149 patients coming to the emergency department with sore throats. (20) Doctors’ clinical impressions were compares to results of throat cultures for group streptococcus. Thirty-seven patients had positive throat cultures, and 27 of these were diagnosed by doctors as having strep throat. One hundred twelve patients had negative cultures, and doctors diagnosed 35 of those as having strep throat.
If the doctor thought the patient had strep throat, for what percent of patients was she correct?
Positive predictive value = 27/62 = 44%
Solution:
First, determine the numbers for each of the four cells: a=27; b-35; c=37-27 (or 10); d=112-35 (or 77)
2013-18
A study was made of clinicians’ ability to diagnose infection on 149 patients coming to the emergency department with sore throats. (20) Doctors’ clinical impressions were compares to results of throat cultures for group streptococcus. Thirty-seven patients had positive throat cultures, and 27 of these were diagnosed by doctors as having strep throat. One hundred twelve patients had negative cultures, and doctors diagnosed 35 of those as having strep throat.
If the doctor thought the patient did not have strep throat, for what percent was he correct?
Negative predictive value = 77/87 = .89
Solution:
First, determine the numbers for each of the four cells: a=27; b-35; c=37-27 (or 10); d=112-35 (or 77)
2013-18
A study was made of clinicians’ ability to diagnose infection on 149 patients coming to the emergency department with sore throats. (20) Doctors’ clinical impressions were compares to results of throat cultures for group streptococcus. Thirty-seven patients had positive throat cultures, and 27 of these were diagnosed by doctors as having strep throat. One hundred twelve patients had negative cultures, and doctors diagnosed 35 of those as having strep throat.
How common was strep throat in patients coming to the emergency department?
Prevalence of strep throat in this emergency room = 37/149 = 25%
Solution:
First, determine the numbers for each of the four cells: a=27; b-35; c=37-27 (or 10); d=112-35 (or 77)
2013-18
A study was made of clinicians’ ability to diagnose infection on 149 patients coming to the emergency department with sore throats. (20) Doctors’ clinical impressions were compares to results of throat cultures for group streptococcus. Thirty-seven patients had positive throat cultures, and 27 of these were diagnosed by doctors as having strep throat. One hundred twelve patients had negative cultures, and doctors diagnosed 35 of those as having strep throat.
Calculate the posttest probability of a clinical impression of strep throat in this study.
LR+ = {[27/(27+10)]} / [35/(35+77) = 2.3
Pretest odds = prevalence/ (1-prevalence) = 0.25/(1-0.25) =1/3
Posttest odds = LR+ x pretest odds = 2.3 x 1/3 = .77
Posttest probability = posttest odds/ (1 + posttest odds) = 0.77/(1 + 0.77) = 0.44 or 44%
(simpler approach is that posttest probability = positive predictive value
+PV = 27/62 = 44%)
2013-18
T or F: Overall, clinical impression of doctors about whether a patient has strep throat is about the same as flipping a coin to decide whether a patient has strep throat.
F
Accuracy of physician impression is (27 + 77)/149 = .70 or 70%, which is better than a coin toss.
2013-18
T or F: Overall, clinical impression of doctors about whether a patient has strep throat could be affected if doctors knew results of the throat cultures when recording their clinical impressions.
T
Knowing the results of the “gold standard” would likely influence the physicians’ clinical impression of whether or not the patient’s sore throat is due to strep infection.
2013-18
T or F: Overall, clinical impression of doctors about whether a patient has strep throat could be affected if only some patients with sore throats got throat cultures.
T
If only certain patients with sore throats are selected for throat cultures, the spectrum of patients would be altered and may affect calculations of the test characteristics.
2013-18
T or F: Overall, clinical impression of doctors about whether a patient has strep throat is sufficiently accurate that no other testing is necessary.
T or F, depending of the medical environment. In a medical setting in which throat culture is not available, such as in many areas of developing countries, clinical impression is better than nothing. However, in most clinical settings in the Unites States, this is an example of a test that is not accurate enough to stop testing. Either a throat culture, the gold standard, or a rapid antigen detection test with culture of negative results is used in these settings.
2013-18
What is the formula of: sensitivity
a/ (a+c)
2013-18
What is the formula of: specificity
d/ (b+d)
2013-18
What is the formula of: PPV
a/ (a+b)
2013-18
What is the formula of: NPV
d/ (c+d)
2013-18
A general practitioner will require a diagnostic test that is highly _______.
a. Specific
b. Sensitive
c. Accurate
d. Reliable
B
