Examkin

Question

Difficulty: EasyDiagnostic Testing Performance

A 32-year-old man comes to a public health clinic for a sexually transmitted infection screening. The physician considers using a newly implemented point-of-care serologic assay for *Treponema pallidum*. To evaluate the reliability of a positive result, the physician reviews a recent local validation study involving 500 high-risk patients.

In this study, 150 patients tested positive using the new point-of-care assay. Subsequent gold-standard confirmatory testing revealed that 135 of these 150 patients were truly infected. The remaining 350 patients tested negative with the new assay, and 315 of them were confirmed to be truly free of the disease by the gold standard.

Based on these study data, what is the positive predictive value (in percentage) of the new point-of-care assay?

Answer: 90 %

Answer

90
The positive predictive value (PPV) answers the clinical question: 'If a patient tests positive, what is the chance they actually have the disease?' It is calculated by dividing the number of true positive results by the total number of positive results. In this validation study, 150 patients tested positive (total positives). Of these, 135 were confirmed to truly have the infection (true positives). The calculation is 135/150=0.90135 / 150 = 0.90, which corresponds to a PPV of 90%90\%.

Step-by-Step Solution

1
Identify the total number of positive test results in the study.
A total of 150 patients tested positive with the new point-of-care assay.
The denominator for positive predictive value is the total number of individuals who tested positive.
2
Identify the number of true positive results.
Among the 150 who tested positive, 135 were truly infected.
The numerator for positive predictive value is the number of individuals who tested positive and actually have the disease.
3
Calculate the Positive Predictive Value (PPV) by dividing true positives by total positives.
135/150=0.90135 / 150 = 0.90, which is 90%90\%.
This directly yields the probability that a patient with a positive test actually has the disease.

Key Concept

The positive predictive value (PPV) is the proportion of positive test results that are true positives, representing the probability that a patient with a positive test actually has the disease.
Estimated Time:45s
Rate this question

Topics

Diagnostic Testing Performance

More questions from this topic