Diagnosis of subclinical rickets.

44 randomly selected infants under age one year with suspected lower respiratory infections were investigated for the presence of subclinical rickets. Seven infants had metaphyseal changes at the wrist compatible with a diagnosis of rickets and all of these infants had 25-hydroxy-vitamin D (25-OHD) concentrations less than 12 ng/ml. Serum calcium and phosphorus concentrations were normal in all 44 children. Alkaline phosphatase concentrations did not correlate with the presence of metaphyseal changes. The clinical presence of craniotabes or splaying and loss of definition of the anterior ends of the ribs on x-rays did not correlate with metaphyseal changes at the wrist or with 25-OHD concentrations. An x-ray of the wrist is essential to confirm the presence of subclinical rickets and the at-risk infant can be detected by measuring serum 25-OHD concentrations.