Nearly 1 in 10 Americans have diabetes, and the number keeps growing. Diabetes is the leading cause of chronic kidney disease (CKD), with 44% of all cases of kidney failure the result of diabetes. By the time patients are in kidney failure, called end-stage renal disease, they require dialysis or transplantation.
The 2.5-hour symposium on August 2 at the 68th AACC Annual Scientific Meeting & Clinical Lab Expo, Diabetic Nephropathy: Where Are We Now? is designed to explore issues related to key biomarkers for diabetic kidney disease (creatinine, glomerular filtration rate [eGFR], cystatin C, and urine albumin) in the context of physiologic and laboratory limitations that may influence interpretation of the results. Speakers will also explain how clinicians use eGFR to make treatment decisions, and explore whether current biomarkers are adequate for assessing renal function in diabetes.
“Because CKD is asymptomatic until fairly advanced, it is difficult to identify a reference population that is free of CKD to establish a reference interval for creatinine,” said Greg Miller, PhD, of Virginia Commonwealth University in Richmond, who is leading the session. “Consequently, the upper reference interval for creatinine is consistent with loss of approximately half of kidney function.”
Thus, he said, “it is essential that laboratories report eGFR to better reflect the status of kidney function so that people with early CKD can be identified.”
Meanwhile, he said, specimens from people with diabetes show fairly common positive interferences with some Jaffe methods, but not with enzymatic methods for creatinine. This, he said, suggests that enzymatic methods are preferred for this population.
Miller and his co-speakers, Andrew Narva, MD, of the National Kidney Disease Education Program at the National Institute of Diabetes and Digestive and Kidney Diseases, and Katherine Tuttle, MD, FASN, FACP, of Washington State University in Spokane, will also discuss new equations for eGFR.
The value is most commonly calculated from creatinine, age, gender, and race. The 2012 Kidney Disease Improving Global Outcomes guidelines added a recommendation to also use cystatin C when calculating an eGFR based on creatinine 45-59 mL/min/1.73 m2 and urinary albumin concentration <30 mg/G to clarify the risk classification at this critical threshold for treatment decisions, Miller explained.
The principal advantage of cystatin C, Miller said, is for use in children and older adults, in whom creatinine-based eGFR is less reliable, or in patients with conditions such as unusual muscle mass.
“The laboratory challenge is that not all commercial methods for measuring cystatin C have calibration traceable to the certified reference material ERM-DA471/IFCC introduced in 2010,” he said. “It is essential that a correctly standardized cystatin C method be used in an eGFR equation.”
Another limitation, he continued, is that not all in-vitro diagnostic manufacturers offer a cystatin C measurement procedure.
Miller expects participants in this session will better understand the classification of CKD based on biomarkers and the relationship of creatinine and eGFR to kidney function. They will also have a better appreciation for the challenges of creatinine measurement in other parts of the world, and potential shortcomings with the use of cystatin C in calculating eGFR.
This session was developed in conjunction with the American Diabetes Association and the AACC Committee on Clinical Collaborations.