Estimating glomerular filtration rate via cystatin-C in preterm infants: a comparative analysis

Background Glomerular filtration rate (GFR) is considered the best marker of renal function. Until the 36^th week of gestation, GFR gradually increases due to increased size and number of nephrons. Renal clearance of inulin is known as the gold standard marker to measure eGFR. Serum cystatin-C (sCysC) is a cationic cysteine protease inhibitor produced at a constant rate from all nucleated cells and not related to infant age, gender, muscle mass, inflammation, or nutritional status. Serum creatinine (sCr) level is dependent on age, gender, maternal renal function, muscle mass, and catabolic status. Objective To determine the course of sCr, sCysC, and urine cystatin-C (uCysC) levels as well as calculate estimated glomerular filtration rate (eGFR) using sCr-and sCysC-based formulas in preterm infants in the first 28 days of life. Methods A total of 52 neonates were included in this prospective study. The neonates were divided into three groups according to gestational age (GA): group 1 (GA ≤28 weeks, 15 subjects), group 2 (GA 29-31 weeks, 16 subjects), and group 3 (GA 32-34 weeks, 21 subjects). Blood and urine specimens were obtained at 24-48 hours of life and then weekly until the 28th day of life. The value and course of eGFR was determined by sCr-and sCysC-based formulas. Results The sCr level was negatively correlated with GA (r=-0.36; P=0.014), but not with BW (r=-0.15; P=0.31). While sCr levels showed significant variations in all study groups on day 7, day 14, and day 21, sCysC did not differ among groups at any time points. All study groups had significantly different uCysC levels, except at day 28. Conclusion In preterm infants, eGFR results calculated with a sCr-based formula are detected to be closer to the inulin values. Therefore, sCr is more reliable for calculating eGFR than sCysC.