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Objective To evaluate clinical and biochemical predictors of metabolic bone disease in preterm infants and determine the diagnostic performance of serum biomarkers for radiographic osteopenia.Design Retrospective cohort study.Setting Level III tertiary neonatal intensive care unit, King Abdulaziz Medical City, Riyadh, Saudi Arabia.Patients 484 infants born at <28 weeks’ gestation or birth weight <1000 g enrolled in a structured Bone Health Programme (2017–2024); infants who died before 4 weeks or had skeletal dysplasia/genetic bone disease were excluded.Main outcome measures Radiographic osteopenia on standardised anteroposterior babygrams. Biomarkers included parathyroid hormone (PTH), alkaline phosphatase (ALP), phosphate and 25-OH vitamin D. A paediatric radiologist, blinded to biochemistry, classified images using predefined criteria. Predictive accuracy was assessed with receiver operating characteristic (ROC) analysis; non-parametric tests were used for group comparisons.Results Biochemical abnormalities were common: hypophosphataemia <1.8 mmol/L in 38% and <1.6 mmol/L in 25%; elevated PTH >10 pmol/L in 77% and >18 pmol/L in 43%; ALP >500 IU/L in 21%; vitamin D <50 nmol/L in 41%. Radiographic osteopenia occurred in 35/484 (7.2%), including 9 fractures (1.9% of the cohort; 25.7% of osteopenia). Compared with infants without osteopenia, affected infants had higher peak PTH (33.2 vs 19.6 pmol/L, p<0.001), screening PTH (21.4 vs 14.2 pmol/L, p=0.002) and peak ALP (558 vs 427 IU/L, p=0.006). On ROC analysis, peak PTH showed the best discrimination for radiographic osteopenia (area under the curve, AUC 0.821, 95% CI 0.754 to 0.889; optimal cut-off >28.7 pmol/L), followed by screening PTH (AUC 0.761, 95% CI 0.676 to 0.845; cut-off >17.6 pmol/L) and peak ALP (AUC 0.657, 95% CI 0.563 to 0.750; cut-off >525 IU/L).Conclusions In this large single-centre cohort, peak PTH was the most accurate biochemical marker for radiographic osteopenia, outperforming ALP and phosphate. Incorporating PTH into routine screening, alongside ALP and phosphate, may improve early identification and targeted mineral optimisation, potentially reducing fractures and streamlining follow-up.