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Difficulty: MediumDiagnostic and Screening Test Performance

A 55-year-old man visits his primary care physician to discuss prostate cancer screening. The physician explains the use of prostate-specific antigen (PSA) testing. The hospital laboratory recently announced a change in their reporting guidelines: the threshold for an "abnormal" PSA result, which triggers a recommendation for a biopsy, has been increased from 4.0 ng/mL to 5.0 ng/mL. The laboratory implemented this change to reduce the number of patients undergoing unnecessary prostate biopsies. Which of the following changes in the test's performance characteristics is the most likely consequence of increasing this cutoff threshold?

  1. Increased false-negative rate and increased positive predictive valueAnswer
  2. B
    Increased false-negative rate and decreased positive predictive value
  3. C
    Decreased false-negative rate and increased positive predictive value
  4. D
    Decreased false-negative rate and decreased positive predictive value
  5. E
    Decreased false-positive rate and increased negative predictive value

Answer

Increased false-negative rate and increased positive predictive value
Increasing the cutoff threshold for a diagnostic test makes the criteria for a positive result more stringent. This directly decreases the number of false positives, effectively increasing the test's specificity. Because there are fewer false positives diluting the pool of positive results, the proportion of true positives among all positive tests rises, leading to an increased positive predictive value (PPV). However, this stricter criterion also means more patients who actually have the disease will incorrectly test negative. This decreases the test's sensitivity and inherently increases the false-negative rate. Therefore, the expected impact is an increased false-negative rate combined with an increased positive predictive value.

Step-by-Step Solution

1
Determine how raising the cutoff threshold affects the likelihood of testing positive.
A higher threshold (from 4.0 to 5.0 ng/mL) means fewer patients overall will have a positive test result.
The test criteria have become more strict, requiring a higher biomarker level to be flagged as abnormal.
2
Analyze the impact on sensitivity and specificity.
Sensitivity decreases (more diseased patients missed) and specificity increases (fewer healthy patients falsely flagged).
Sensitivity and specificity have an inverse relationship when adjusting a single continuous variable cutoff.
3
Translate these changes into error rates and predictive values.
Decreased sensitivity means the false-negative rate increases. Increased specificity reduces the false-positive rate, which in turn increases the positive predictive value.
Positive predictive value is highly dependent on specificity; eliminating false positives increases the proportion of true positives among all positive results.

Key Concept

Raising the cutoff threshold for a diagnostic test increases specificity (and positive predictive value) while decreasing sensitivity, which consequently increases the false-negative rate.
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Diagnostic and Screening Test Performance

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