Sensitivity/Specificity Question

[Masato Kobayashi]

Referencing the question below:
64. A 56-year-old female presents to the emergency department via ambulance 45 minutes after she collapsed in the bathroom at the office where she works as a marketing executive. The patient’s medical history is remarkable for hypertension, type II diabetes mellitus, and atrial fibrillation. Upon arrival, the patient is confused and dependent for transfers. Given the sudden change in status, a stroke is suspected.

Scores on the Postural Assessment Scale for Stroke Patients are predictive of future ambulatory ability. Total scores greater than 12.5/36 predict independence with ambulation at discharge from inpatient rehabilitation with 78.9% sensitivity and 83.7% specificity. The patient’s score on the PASS was 13. What conclusion is most appropriate?

a. High confidence that the patient will be independently ambulatory upon discharge from inpatient rehabilitation due to the high sensitivity of the PASS
correct
b. High confidence that the patient will be independently ambulatory upon discharge from inpatient rehabilitation due to the high specificity of the PASS
c. Low confidence that the patient will be independently ambulatory upon discharge from inpatient rehabilitation due to the low sensitivity of the PASS
d. Low confidence that the patient will be independently ambulatory upon discharge from inpatient rehabilitation due to the low specificity of the PASS

Explanation: Sensitivity is the true positive rate – or the likelihood that the score will be positive (>12.5) given the person has the condition (future independence with ambulation). Specificity is the true negative rate – or the likelihood that the score will be negative (<12.5) given the person does not have the condition. The PASS has fairly high sensitivity and specificity – so, because this patient scored >12.5, we are fairly confident she will be independently ambulatory in the future. Highly sensitive tests are most useful for ruling IN conditions if the test result is positive. Highly specific tests are most useful for ruling OUT conditions if test results are negative. Therefore, because this patient’s test result was positive (>12.5/36), we are confident that the patient will be independently ambulatory due to the sensitivity of the PASS.

My question – if the patient scored less than the cut-off of 12.5, would the correct answer be something along the lines of “high confidence that patient will NOT be independent with ambulation upon discharge from inpatient rehab due to high specificity of the PASS?”

Just want to make sure I’m understanding both sensitivity and specificity correctly.

[Chrissy Durrough Lugge]

Hi Masato! Correct – this PASS has a fairly high specificity, which tells us the true negative rate. If the patient had a negative result (meaning he scored less than 12.5 on the PASS), we would have high confidence that he would not be independently ambulatory at discharge due to the PASS’s 83.7% specificity. 🙂

[Author]

Posts