Serum cystatin C levels were similar in adolescents with and without type 1 diabetes. As previously reported in nondiabetic adolescents in NHANES data, age, sex, and serum creatinine are all associated with cystatin C levels (5
). Our data demonstrate similar cross-sectional associations in nondiabetic adolescents, and expand this observation to adolescents with type 1 diabetes in a cohort that includes nondiabetic control subjects. In adolescents with type 1 diabetes or nondiabetic control subjects, cystatin C levels decrease on average by 0.02 mg/L every year from 12–19 years of age, and in type 1 subjects, these levels are 0.039 mg/L higher in males than in females, similar to NHANES data (5
). These data suggest sex differences and age-related changes in cystatin C during adolescence in this population with implications for its use as a marker of renal function. Further study on whether these data reflect changes in the biomarker or a true change in GFR is needed.
Our data have limitations to consider. First, these data, like those reported from NHANES (5
), are cross-sectional. Second, we do not have data on all of the markers examined by Groesbeck et al. (5
), including blood urea nitrogen, uric acid, and fat-free mass. Additionally, our cohort is predominantly non-Hispanic white (77%), and we do not have statistical power to investigate differences in cystatin C by race/ethnicity and associations within the nondiabetic subjects, such as sex, which was not significantly associated in the multivariable model. Further data are needed on cystatin C in minority youth with diabetes.
Identification of biomarkers to improve clinical decision making to monitor and prevent diabetic kidney disease is needed, and cystatin C has emerged as perhaps the most promising biomarker (7
). Early identification of incipient diabetic kidney disease and risk stratification for who will progress to clinical diabetic nephropathy remains a major research priority for preventing diabetes complications, including renal disease itself (1
), and as a risk factor for cardiovascular disease and mortality (8,9). Moreover, collection of urine samples from adolescents presents a challenge in clinical care; therefore, a biomarker not requiring fasting or overnight collection would improve current screening and diagnostic capabilities. However, before widespread clinical use, issues such as assay standardization and consistency need to be addressed (7
). In a cohort of adults with and without type 1 diabetes, we reported a 10–15% systematic shift, corrected by regression adjustment, in the commercially available Dade-Behring cystatin C assay between 2006 and 2010 (10
Understanding these reported age- and sex-related effects on cystatin C in adolescents (which are similar by diabetes status) is a first step in determining the potential role of cystatin C to diagnose and then monitor changes in early renal disease in adolescents with type 1 diabetes.