Creatinine Filtration Kinetics in Critically Ill Neonates

BACKGROUND: Creatinine values are unreliable within the first weeks of life; however, creatinine is used most commonly to assess kidney function. Controversy remains surrounding the time required for neonates to clear maternal creatinine. METHODS: Eligible infants had multiple creatinine lab values and were admitted to the NICU. A mathematical model was fit to the lab data to estimate the filtration onset delay, creatinine filtration half-life, and steady-state creatinine concentration for each subject. Infants were grouped by gestational age (GA) [(1)22-27, (2)>27-32, (3)>32-37, and (4)>37-42 weeks]. RESULTS: 4,808 neonates with mean GA 34.4 ± 5 weeks and birth weight 2.34 ± 1.1 kg were enrolled. Median (95% CI) filtration onset delay for Group 1 was 4.3 (3.71,4.89) days and was significantly different than all other groups (p<0.001). Creatinine filtration half-life of Groups 1, 2, and 3 were significantly different from each other (p<0.001). There was no difference in steady-state creatinine concentration amongst the groups. CONCLUSION: We quantified the observed kidney behavior in a large NICU population as a function of day of life and GA using creatinine lab results. These results can be used to interpret individual creatinine labs for infants to detect those most at-risk for acute kidney injury.