Identification of renal dysfunction in critically ill children is often delayed due to lack of accurate methods for evaluation of glomerular filtration rate (GFR). The investigators compared GFR measurement by the gold standard technique iohexol plasma clearance with estimated GFR (eGFR) based on selected established formulas incorporating the renal biomarkers creatinine, cystatin C and betatrace protein.

Acute kidney injury (AKI) is a frequent comorbidity of critical illness associated with poor outcome, including prolonged duration of mechanical ventilation, longer length of stay and increased mortality or progression to chronic kidney disease on the long term. The reported incidence of AKI in critically ill children and neonates varies widely between 10% and 80% depending on the diagnostic criteria. Besides a decline in renal function, also the phenomenon of augmented renal clearance (ARC) and in consequence enhanced clearance of renally eliminated drugs, is increasingly recognized in pediatric intensive care patients. Hence, accurate assessment of renal function is crucial in the intensive care population to guide therapy. But to date consensus is lacking about the reliability of common GFR estimation methods based on the endogenous renal biomarkers serum creatinine, cystatin C and betatrace protein in critical care patients. the aim of this study is to measure GFR in a reliable way by iohexol plasma clearance and evaluate the agreement between the gold standard technique iohexol plasma clearance and biomarker-based formula to estimate GFR.

Inclusion criteria:

• patients admitted to the pediatric or neonatal intensive care unit
• 0 - 15 years
• for neonates: gestational age ≥ 37 weeks
• bodyweight >2.5kg
• intra-arterial and/or intravenous access available for iohexol administration and blood sampling

Exclusion criteria:

• no vascular access in place for iohexol administration and blood sampling
• absence of parental/patient consent
• known hypersensitivity to contrast media or previous history of adverse reaction after administration of contrast agents
• known thyroid dysfunction, or for newborns: mother with known thyroid dysfunction
• extracorporeal circuit (haemodialysis, extra corporal membrane oxygenation (ECMO), peritoneal dialysis)
• patients with chronic kidney disease or congenital kidney anomalies
• preterm neonates (gestational age < 37 weeks)
• body weight < 2.5 kg
• dehydrated newborns (i.e. loss of birth weight ≥ 10%)
• planned/expected surgery with extracorporeal circulation within 5 days after inclusion