Validating Obstructive Genitourinary Defects in an Environment of Potential Overdiagnosing

The mission of the Department of Defense Birth and Infant Health Registry (Registry) is to conduct ongoing surveillance of birth defects among military families, following the National Birth Defects Prevention Network (NBDPN) case definitions. From 2009 to 2011, a 30% increase in diagnoses of obstructive genitourinary defects (OGDs) was observed in the Registry. To explore the source of this finding, we identified the location with the highest increase and conducted a validation study for OGD cases.

The study population consisted of a random sample of 30 infants defined as OGD cases in the Registry (2010-2011), born at 1 specific military hospital. OGD cases were defined by the presence of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnostic codes 753.2 and/or 753.6 in administrative claims data. A physician reviewed electronic medical records for each infant to confirm true OGD cases and a positive predictive value and 95% CI was calculated.

Physician review confirmed only 10% (95% CI, 2%-27%) of the random sample of OGD cases (n = 30) from the identified hospital as true cases. Approximately 97% of infants in this sample were assigned the less severe ICD-9-CM code, 753.2.

These results support the 2014 modifications to the NBDPN OGD case definition, which excluded from reporting ICD-9-CM diagnostic code 753.2, which is the less severe OGD diagnosis that may spontaneously resolve without the need for intervention and is more likely to increase the number of false positive cases.