Purpose: Acute Kidney Injury (AKI) in Very Low Birth Weight (VLBW) infants can cause interruptions to nephrogenesis and result in functional renal loss. Serum Creatinine (S.Cr), although a useful marker for the diagnosis of AKI, is not reliable in monitoring ongoing renal dysfunction due to the lack of normal baseline values. On the other hand, glomerular filtration rate (GFR) is a better measure of ongoing renal dysfunction as it represents S.Cr values in relation to height and age dependent constant values. Effect of early injury to the developing kidneys can be estimated by tracking GFR in these patients over time. In this study, we intend to examine the impact of early AKI on GFR in VLBW infants during the first month of life. Methods: We conducted a retrospective chart analysis of VLBW infants admitted to a single-center tertiary level NICU between August 2012 and April 2015. We identified infants with AKI based on the Acute Kidney Injury Network (AKIN) criteria and compared them at a 1:2 ratio with gestational age (GA)-, birth-weight (BW)- and gender-matched controls without AKI. Average GFR computed using weekly S.Cr and height [using equation GFR (ml/min/1.73 sq.m) = 0.33*Height (cm)/S.Cr (mg/dl)] was compared between these two groups during weeks 1, 2, 3 and 4. Contributions of other co-morbid conditions and nephrotoxic drugs to poor GFR were also analyzed using a regression model. Results: o Fifty-five infants with AKI were identified during the 2.5-year time-period and compared to 110 matched controls. o Median age at onset of AKI was 6 days. o Average GA and BW of infants in the AKI and non-AKI groups were 25.47 vs 27.12 weeks and 759.05 vs 943.71 grams, respectively. o Presence of AKI was the single most predictive factor for poor GFR in the first month of life. o Average weekly GFR was significantly lower during weeks 1, 2, 3 and 4 in infants with AKI compared to controls (Table 1). o In addition to AKI, other significant predictors of poor GFR in this population included: o Week 1: Lower GA and BW o Week 2: Lower GA and presence of PDA o Week 3: Indomethacin use o Week 4: Higher percentage of weight loss since birth Conclusion: VLBW infants with early onset AKI had persistently poor renal function during the first month of life compared to infants without AKI. GFR remained low in these patients despite stabilizing creatinine values following the initial surge. GFR should therefore be monitored in all patients with AKI. Infants with persistently low or worsening GFR should be appropriately referred and evaluated for chronic kidney disease.