To assess the relationship between radiographic findings of metabolic bone disease (MBD) and serum biochemical markers in preterm infants.

A total of 159 preterm infants were included in this study. Two readers reviewed the wrist radiography for grading according to MBD severity. We recorded the levels of alkaline phosphatase (ALP) and phosphorous (P) immediately after birth, on the same day of the first wrist radiography (ALP-s, P-s), the highest/lowest ALP/P levels before the first wrist radiography (ALP-hb/P-lb) and during follow-up (ALP-h/P-l). For analysis, the patients were first subdivided into 4 groups according to MBD severity, and were then divided into 2 groups according to MBD presence or absence.

Of the 159 patients, 94, 39, 19, and 7 infants were classified into grades 0,1, 2, and 3. Analysis according to severity showed that ALP-s, ALP-hb, and ALP-h differed between grades 0–1 and 2–3 (all P<0.001); P-lb differed between grades 0 and 2 (P=0.001); and P-l differed between grades 0 and 2 or 3 (P<0.001 or P=0.001). Moreover, ALP-s, ALP-hb, ALP-h, P-s, P-lb, and P-l differed according to the presence or absence of MBD (P<0.001). ALP-h showed the largest area under the curve value (0.752, 95% confidence interval=0.676–0.828, P<0.001). The optimal cut-off value of ALP-h was 473.5U/L. The sensitivity and specificity were 81.5% and 47.9%. ALP-h was measured at 6.9±5.3 weeks after birth.

Taking the wrist radiography with reference to an ALP level measured at around 6.9 weeks after birth could be helpful for screening of MBD in preterm infants, unless a fracture is clinically suspected.