In the July 2002 issue of Pediatrics, Engle et al conclude that in a population of infants at risk for hyperbilirubinemia who are referred for retesting, transcutaneous bilirubinometry has limited usefulness. This study and many like it are quite necessary, but in this case, the result was very predictable provided one accepts the following:

Engle’s population consisted of infants in whom “the primary caregiver determined that clinically apparent jaundice necessitated retesting.” In contrast, Bhutani et al (who reported on the same device) selected a population who, for the most part, had testing done at the time of routine metabolic screening or essentially were all “well” newborns. Presumably, some of these infants newborns will later become jaundiced and some will not. Thus, the spectrum of patients tested in each study was different.

The specificity of a test answers the question, “If a patient does not have disease,...

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