Examkin

Soru

Zorluk: OrtaDiagnostic Testing Performance

An infection control committee at a large urban medical center evaluates the ongoing use of a rapid nucleic acid amplification test (NAAT) for a seasonal viral pathogen. The manufacturer data indicates the test has a sensitivity of 94% and a specificity of 97%. During the winter peak, the prevalence of the viral infection among patients presenting with acute respiratory symptoms is 25%. By mid-summer, the prevalence in the same symptomatic population decreases to 2%. A physician considers ordering the NAAT for a patient presenting with a cough in July.

Compared to testing performed during the winter peak, which of the following best describes the statistical implications of using this test during the mid-summer period?

  1. A higher proportion of positive test results will be false positivesCevap
  2. B
    A higher proportion of negative test results will be false negatives
  3. C
    The test will fail to identify a greater percentage of the truly infected patients
  4. D
    The test will falsely identify a greater percentage of uninfected patients as having the disease
  5. E
    The ratio of the probability of a positive test in infected patients to uninfected patients will decrease

Cevap

A higher proportion of positive test results will be false positives
The correct answer accurately describes the effect of decreased prevalence on the Positive Predictive Value (PPV). In the summer, the disease is much rarer (2% prevalence). When a disease is rare, the absolute number of true positive results drops significantly. However, the test will still produce false positives at a constant rate (1 - 0.97 = 3%) from the now much larger pool of uninfected patients. Consequently, the false positives make up a much larger proportion of the total positive results, meaning the PPV has decreased.

Adım Adım Çözüm

1
Identify the changing variable in the clinical scenario.
The prevalence of the disease decreases significantly from 25% in the winter to 2% in the summer, while the intrinsic test characteristics (sensitivity and specificity) remain constant.
Prevalence is the primary epidemiological variable that shifts between seasons.
2
Determine how the change in prevalence affects the predictive values of the test.
A decrease in disease prevalence leads to a decrease in Positive Predictive Value (PPV) and an increase in Negative Predictive Value (NPV).
When a disease is rare, even a highly specific test will produce a number of false positives that equals or outnumbers the true positives, lowering the PPV.
3
Translate the change in PPV to the clinical outcomes described in the options.
PPV is the proportion of true positives among all positive tests. If PPV decreases, the remaining proportion of positive tests (which are false positives) must increase.
The sum of the proportion of true positives and false positives among all positive results is always 100%. Therefore, a lower PPV directly equates to a higher False Discovery Rate (proportion of false positives among all positives).

Anahtar Kavram

Positive and Negative Predictive Values are highly dependent on disease prevalence; as prevalence decreases, Positive Predictive Value decreases and the proportion of false positives among all positive results increases.
Tahmini Süre:1m 30s
Bu soruyu puanla

Konular

Diagnostic Testing Performance

Bu konudan daha fazla soru