Validation of early biomarkers in urine: studies in healthy subjects and cardiac patients

Abstract

Background: The novel urinary biomarkers for the early detection of kidney injury after ischemic or toxic insults have recently been well studied, including neutrophil gelatinase associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), cystatin C (Cys-C)and Nacetyl- β Dglucosaminidase (NAG). The lack of reference values have greatly impeded progress in the diagnosis and treatment of patients with AKI and have a detrimental effect on the possibly outcomes of clinical trials of cardiac surgery. Objective: The first objective of this study was to estimate the normal value of urinary NGAL, KIM-1, Cys-C and NAG in a healthy population. The second objective was to evaluate the diagnostic performance of urinary biomarkers in a prospective pilot study including adults after cardiopulmonary bypass (CPB) surgery. Methods: The age study population consist of 337 healthy non-smoking subjects (191 female, 146 male ranging from 4 months to 90 years). Urine samples were obtained at routine visit to the ZOL hospital. ELISA was used to measure urinary NGAL, KIM-1 and Cys-C. BIOQuant N-acetyl-B-D-Glucosaminidase (NAG) assay was used to measure NAG. The prospective pilot study consists of 25 adults (7 females, 18 males ranging from 51 to 84 years) who required CPB surgery. Urine and blood samples were obtained before and 3, 6, 12 and 24 hours after CPB surgery. Patients were divided into the AKI and non-AKI groups according to developed AKI after surgery, AKI was defined as a ≥ 0.3 mg/dl increase in sCr from the base line within 48h after the surgery. Urinary KIM-1 and NGAL were measured using ELISA assay. Results: Age study: significant age related differences were found for KIM-1, NGAL, Cys- C and NAG. In addition, significant differences between gender were found for KIM-1, NGAL and NAG. Cardiac study: 25 patients were enrolled, 20% developed AKI. Urinary KIM-1/Cr level was significantly increased 24h post surgery and was significantly associated with AKI within 24h ,while urinary NGAL level did not show such a performance. Conclusions: Based on our results, further study in larger population with biomarker panel is needed for the evaluation of normal values with variance factors as well as to establish the prediction value to diagnose AKI for long and short outcomes after cardiac surgery.