The Utility of the Creatinine Excretion to Production Ratio and the Plasma Creatinine and Cystatin C Based Kinetic Estimates of Glomerular Filtration Rates in Critically Ill Patients with Sepsis

INTRODUCTION: Creatinine kinetics denotes that under steady-state conditions, creatinine production (G) will equal creatinine excretion rate (E). The glomerular filtration (GFR) is impaired when excretion is less than production. The kinetic estimate of GFR (keGFR) and E/G ratio were proposed as a more accurate estimate of GFR in acute settings with rapidly changing kidney function. We evaluated keGFR and E/G to diagnose AKI, predict recovery, death or dialysis.

METHODS: This is a prospective observational study of critically ill patients. Inclusion criteria were patients >18 years old with sepsis, defined as clinical infection with an increase in SOFA score >2, and plasma procalcitonin >0.5 ng/mL. Plasma creatinine and Cystatin C were measured on ICU admission and 4 h later, and their keGFR was calculated. Urine creatinine and urine output were measured over 4 h to calculate the E/G ratio.

RESULTS: A total of 70 patients were recruited, of which 49 (70%) had AKI. Of these, 33 recovered within 3 days, and 15 had a composite outcome of death or dialysis. Day 1 keGFRCr and keGFRCysC discriminated AKI from non-AKI with AUCs of 0.85 (95% Confidence interval: 0.74-0.96), and 0.86 (0.76-0.97), respectively. The E/G ratio predicted AKI recovery (AUC: 0.81 (0.69-0.97)). The keGFRs were not predictive of death or dialysis, whereas E/G was predictive (AUC: 0.76 (0.63-0.89).

CONCLUSION: keGFR was strongly diagnostic of AKI. The E/G ratio predicted AKI recovery and a composite outcome of death and dialysis.