Relationship between initial serum creatinine after birth and subsequent changes to the peak level in preterm neonates

Background In preterm neonates, the postnatal course of serum creatinine is influenced by maternal serum creatinine levels and physiological changes after birth. While transient postnatal increases in serum creatinine have been reported, the relationship between the initial value at birth (Cr ₀ ) and subsequent changes to the peak value (ΔCr) has not been clarified. Methods A total of 467 preterm neonates admitted to our neonatal intensive care unit were analyzed after excluding those with conditions or treatments that could affect circulatory dynamics. The peak day of serum creatinine was determined according to gestational age. Simple linear regression analysis was performed to evaluate the correlation between Cr ₀ and ΔCr, and multiple regression analysis was conducted to identify factors associated with ΔCr. Results The serum creatinine peak occurred on day 2 in neonates with gestational age ≤ 29 weeks and day 1 in neonates with gestational age ≥ 30 weeks. Simple regression revealed a significant correlation between Cr ₀ and ΔCr (ΔCr = 0.602 − 0.635 × Cr ₀ , R ²  = 0.423, P  < 0.001); ΔCr was zero when Cr ₀ was 0.95 mg/dL. Multiple regression identified Cr ₀ (β = −0.701, P  < 0.001), 5-minute Apgar score (β = −0.013, P  = 0.009), and 24-hour urine output (β = −0.039, P  < 0.001) as independent factors influencing ΔCr. Conclusions The neonatal serum creatinine levels converge toward 0.95 mg/dL between day 1 and day 2 before declining. These findings provide new insights into physiological serum creatinine changes and may aid interpretation of creatinine-based acute AKI diagnosis in preterm neonates.