Validation of the Q87.11 ICD Code for Prader-Willi Syndrome.
James Luccarelli, Theresa V Strong, Thomas H McCoy
The Q87.11 billing code flags the right patient 96.8% of the time, making it a reliable way for researchers to pull PWS cohorts from claims data.
It reports no treatment outcomes and does not change what a clinician does with a patient.
Key findings
1A single Q87.11 code in a patient's record has a positive predictive value of 96.8% (95% CI 92.0–99.1%) for that person actually having Prader-Willi syndrome, with specificity and negative predictive value both at 100%.
2Per-encounter sensitivity drops substantially: 79.4% (95% CI 62.6–91.1%) for inpatient visits but only 46.0% (95% CI 44.1–47.9%) for outpatient visits, because clinicians often code the acute problem rather than the underlying PWS.
3Among 2,147 patients whose notes mentioned PWS-related terms but who lacked the Q87.11 code, a 10% sample review found only 1 true missed case, yielding an any-time sensitivity of 92.4% (95% CI 68.9–100%).
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How it was doneWhat they found
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What it does not show
Single US health system; coding and documentation practices may differ elsewhere, and the authors explicitly caution against extrapolating outside the US. The PWS cohort is small (122 confirmed cases), and the false-negative estimate rests on a 10% sample of 2,147 text-matched records, giving a wide confidence interval on sensitivity (68.9% to 100%). Full genetic subtyping was unavailable for a significant fraction of patients, so some clinical diagnoses of PWS could not be confirmed molecularly. Retrospective design with a waiver of informed consent; no prospective follow-up or outcome tracking. The 4 false-positive cases include one where the code was applied to a fetus during a genetics evaluation, suggesting the code can be attached to the wrong person in the record.
Declared interests
No funding source or conflict-of-interest declaration is stated in the supplied text.
The easy way to misread this
Do not read the 96.8% positive predictive value as meaning the code is equally reliable on every visit. Per-encounter sensitivity falls to 46% for outpatient encounters, so a patient with PWS may not carry the code on a given clinic visit. Also, the validation was done in one large US academic health system; the authors themselves warn that coding patterns may differ in other settings, so the accuracy figures should not be assumed to hold in a different country or a smaller community hospital.
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