Abstract
Plasma alkaline phosphatase activity was measured in 349 infants aged between 5 and 10 days to establish a normal range for different gestational ages. Significant differences were observed between term and preterm infants, the highest values being associated with the shortest lengths of gestation. Plasma calcium, phosphate, and alkaline phosphatase activity were measured sequentially in 51 preterm infants less than 1500 g at birth. A significant correlation was found between raised plasma alkaline phosphatase activity and radiological changes of osteoporosis, metaphyseal change, and periosteal reaction. Plasma alkaline phosphatase appears to be of value in screening for and monitoring rickets of prematurity.