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• An increase in the expression or activity of ALP suggests osteoblast differentiation. • ALP activity can be an important indicator of metabolic bone diseases. • A percentile curve for ALP activity per month in infants was created. • This curve is a reference for diseases related to abnormal ALP activity in infants. Alkaline phosphatase (ALP) is a ubiquitous enzyme in humans that can be used for diagnosing childhood diseases. Infants have the highest rapid growth rate and are susceptible to metabolic bone diseases. In infants, ALP activities exhibit significant month-wise variations, and authoritative standards are lacking. The present study aimed to provide a reference for the diagnosis of diseases related to abnormal ALP activities in infants. This study included 24,618 samples collected from infants aged 0–12 months from three medical centers in Chongqing, China. Samples of infants diagnosed with diseases that may affect ALP activity have been exclude. ALP activity was analyzed using an automatic biochemical analyzer. A percentile curve for ALP activity in male and female infants was constructed using MATLAB, and the skewness-median-coefficient of variation method was employed for curve fitting. ALP activity in male and female infants peaked at 0–4 months; the peak appeared at 1–2 months and declined gradually thereafter. After 4–5 months of age, the ALP activities declined further, with the lowest values observed at 11–12 months of age. A comparison between the data from this study and a those from a published German study indicates that Chinese infants exhibited peak ALP activity later and subsequent decline greater than German infants. A percentile curve was constructed for month-wise ALP activity in male and female infants, which could provide a reference for diagnosing diseases related to abnormal ALP activity in infants. [ABSTRACT FROM AUTHOR]

Due to the higher birth rate of preterm infants and improvements in their management, metabolic bone disease of prematurity (MBDP) has a high incidence and is attracting attention. However, clear indicators for the early diagnosis of MBDP are lacking. We aimed to explore simple and feasible early warning indicators for diagnosing MBDP. Our study collected case data of premature infants from two medical centers in Chongqing from January 2020 to February 2022. According to the inclusion and exclusion criteria, data from 136 cases were collected. The correlation between 14 variables in each case and the occurrence of MBDP was analyzed. According to area under the receiver operating characteristic curve (AUROC) analysis, the best cutoff value for each variable was determined. Potential predictors were selected, and Least Absolute Shrinkage and Selection Operator (LASSO) regression analysis was used to establish the association of two models with MBDP, whose results were used to develop a diagnostic nomogram. Furthermore, a model decision curve was analyzed. Four predictors were selected from 14 clinical variables by LASSO regression, and Model I was established, including the following characteristics: height (>36 cm), head circumference (≤29.49 cm), total serum calcium (Ca) (>2.13 mmol/L), and alkaline phosphatase (ALP) (>344 U/L) levels. A single predictor, the ALP level (>344 U/L), was used to establish Model II. The AUROC values of the two models were 0.959 for Model I and 0.929 for Model II. In conclusion, in this study, two diagnostic models of MBDP were developed using four combinations of predictors and ALP as a single predictor. Both models showed good sensitivity and specificity for the early diagnosis of metabolic bone disease (MBD), and an ALP level of 344 U/L was defined as a simple and effective diagnostic threshold. In future studies, using larger samples, diagnostic threshold values of ALP for premature infants of different ages should be established, and internal and external validations are needed to improve the adaptability of the current model. • Metabolic bone disease of prematurity (MBDP) has high incidence recently. • No easy-to-measure biomarkers are available for MBDP. • We assessed 4 predictors in 2 models; both showed good sensitivity and specificity. • Alkaline phosphatase 344 U/L is a cutoff for an early warning of metabolic bone disease in premature infants. [ABSTRACT FROM AUTHOR]