Urine and Serum Biomarkers for Early Detection of Acute Kidney Injury

Purpose: This will assess whether sensitive tests for urine or serum biomarkers are able to detect acute kidney injury following cardiopulmonary bypass surgery in the context of congenital heart disease.

Background: Acute kidney injury (AKI) is defined as an abrupt decrease in renal function resulting in retention of nitrogenous (urea and creatinine) and non-nitrogenous waste products. AKI is a common complication following cardiopulmonary bypass (CPB) surgery, occurring in up to 30% of adult patients following CPB surgery, increasing morbidity, mortality, and resource utilization.

Patients with cyanotic heart disease who undergo CPB surgery are also at risk of developing AKI. These patients require multiple surgeries over the course of their lifetime to correct their congenital cardiac lesions. Cyanosis alone causes a glomerulopathy characterized clinically by sub-nephrotic range proteinuria, with higher prevalence related to length of time prior to initial corrective procedures.

Pharmacological strategies for treatment of AKI have shown little efficacy in previous studies. Thus, recent studies have aimed to evaluate novel plasma and urinary biomarkers for early diagnosis of AKI, based on the hypothesis that outcomes may improve if AKI were identified and treatment initiated earlier. Urinary IL-18 and NGAL have been shown to be predictive markers of AKI after cardiopulmonary surgery in a pediatric population with a variety of congenital heart defects. This ultimately reduced detection time from 40 hours with conventional serum creatinine assays, to 4-6 hours with urinary IL-18 and NGAL. Serum Cystatin C has also been shown to be as reliable as serum creatinine in predicting kidney filtration levels, particularly for subjects with reduced muscle mass such as a population with congenital heart disease.

However, no study has evaluated the utility of such markers in a combined pediatric and adult congenital heart disease population. These patients are unique because of the multitude of CPB surgeries required throughout their lifetime, degree of life spent cyanotic and, thus, may differ in their susceptibility to cardiac surgery associated AKI.

Our long term goal is to evaluate the value of urinary and serum biomarkers for early detection of AKI in this unique patient population. Currently, the investigators propose to perform a pilot study to evaluate the feasibility of the study methods and to obtain preliminary data to assist in power calculations for a larger study.

Methods: The investigators will enroll a total of 20 patients undergoing pulmonary valve replacement. All patients will have a history of a conotruncal anomaly with previous corrective surgery requiring cardiopulmonary bypass. Enrollment will occur at the time of cardiology or cardiovascular surgery consultation.

After informed consent and assent is obtained, urine and serum samples will be collected for the study protocol. Urine specimens for creatinine, NGAL, and IL-18 will be collected pre-operatively for baseline measurement in addition to post-operatively at 6, 12, 24, and 72 hours. Cystatin C will be measured pre-operatively to assess chronic renal function. Serum creatinine will be measured pre-operatively and post-operatively at 12 hours and daily as part of usual clinical care.

Patients will be followed for 7 days after surgery or until the day of hospital discharge, whichever occurs first. Data collected from the hospital chart will include: demographics, medical and surgical history, type of surgical procedure, underlying congenital heart disease, baseline serum creatinine and renal function, serum creatinine(s) throughout hospitalization, daily urine output, need for dialysis, date of death or discharge. The primary endpoint is development of AKI based on serum creatinine reaching double baseline or requirement for acute dialysis, as described in the RIFLE- Risk, Injury, Failure, Loss, and End Stage Renal Disease- model of renal insufficiency.