Creatinine filtration kinetics in critically Ill neonates

Abstract

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 neonatal intensive care unit (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: A total of 4808 neonates with a mean GA of 34.4 ± 5 weeks and birth weight of 2.34 ± 1.1 kg were enrolled. Median (95% confidence interval) 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 among the groups.

Conclusions: 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.

Impact: One of the largest cohorts of premature infants to describe the evolution of kidney development and function over their entire hospitalization. New concept introduced of the kidney filtration onset delay, the time needed for the kidney to begin clearance of creatinine, and that it can be used as an early indicator of kidney function. The smallest premature infants from 22 to 27 weeks gestation took the longest time to begin and complete maternal creatinine clearance. Clinicians can easily compare the creatinine level of their patient to the normative curves to improve understanding of kidney function at the bedside.

Figure 1.

10^th to 90^th Percentile curves by group number with highlighted 10^th percentile (blue), 50^th percentile (dashed black line), and 90^th percentile (red line).

Figure 2.

95% Confidence region for moving median for each group

Figure 3.

Mathematical model fit to creatinine lab for one patient from Group 1

Figure 4.

Filtration onset delay in days versus gestational age in weeks by Group

Figure 5.

Half-life for creatinine filtration in days versus gestational age in weeks by Group

Figure 6.

Steady-state creatinine concentration versus gestational age in weeks by Group