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Difficulty: EasyDiagnostic and Screening Test Performance

A hospital committee is reviewing the screening protocol for a newly identified respiratory virus. The current rapid antigen test uses a specific quantitative threshold to determine a positive result. To minimize the number of infected patients who are mistakenly told they do not have the virus, the committee decides to lower the cutoff threshold required for a positive test. Which of the following is the most likely consequence of lowering this cutoff threshold?

  1. Increased sensitivityAnswer
  2. B
    Increased specificity
  3. C
    Increased false-negative rate
  4. D
    Increased positive predictive value
  5. E
    Decreased negative predictive value

Answer

Increased sensitivity
The correct answer is increased sensitivity. Lowering the cutoff threshold for a positive test means that a smaller amount of the measured biomarker is required to trigger a positive result. This causes a larger overall number of patients to test positive. Consequently, more patients who genuinely have the disease will correctly test positive, which increases the number of true positives and decreases the number of false negatives. Because sensitivity is the ability of a test to correctly identify those with the disease, this shift leads directly to an increase in sensitivity.

Step-by-Step Solution

1
Analyze the change in the test threshold
The cutoff threshold for a positive test is lowered, meaning less of the measured antigen is needed to trigger a positive result.
Understanding the directional shift of the cutoff is required to determine its effects on test parameters.
2
Determine the effect on diagnostic populations
A lower cutoff will classify more people overall as 'positive'. This increases both True Positives (catching more infected patients) and False Positives (mislabeling more healthy patients).
Test characteristics are calculated based on the distribution of True Positives, False Positives, True Negatives, and False Negatives.
3
Calculate the impact on specific statistical measures
Because True Positives increase and False Negatives decrease, the sensitivity (TP / [TP + FN]) increases.
Sensitivity specifically measures the proportion of actual positives correctly identified as such.

Key Concept

Effect of shifting diagnostic cutoffs on test performance parameters
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Topics

Diagnostic and Screening Test Performance

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