Abstract
Background/Aims Identifying early chronic kidney disease (CKD) among patients with diabetes impacts the development of diabetic complications, costs, and prevention. Cystatin C may be a better marker for kidney function than serum creatinine (SCr) and estimated glomerular filtration rate (eGFR), however, it is not routinely collected. The purpose of this analysis was to assess the use of cystatin C to measure and describe early CKD.
Methods We recruited members who were English-speakers, non-pregnant, aged 25–74 years, enrolled in the KPG diabetes registry, and reported eGFR > 60 ml/min/1.73m2. Capillary and venous blood samples were collected as well as anthropometric measures and questionnaire data. Descriptive estimates were calculated and prevalence of early CKD was reported by elevated cystatin C (defined as cystatin C >0.1 mg/dl) and eGFR. Cystatin C estimates obtained from venous and capillary blood were compared using Bland-Altman and scatter plots.
Results The mean age of patients was 53 years. Approximately 71% (40 of 56) were African-American, 59% (35 of 59) were female, 7% (4 of 56) had less than a high school education, and 79% (44 of 56) were obese. The means (± SE) for eGFR, cystatin C (venous), and cystatin C (capillary) were 93.1 (2.70) ml/min/1.73m2, 0.72 (0.02) mg/dl, and 0.68 (0.03) mg/dl, respectively. The prevalence of stage 2 CKD was 44% (26 of 59) and stage 3 CKD was 56% (33 of 59). We identified 5% (3 of 59) and 7% (3 of 44) of patients with early stage CKD using cystatin C measures in venous and capillary blood, respectively. The correlation between estimates of cystatin C using venous and capillary blood were high (r = 0.81).
Conclusions In this study of patients with normal eGFR, we found that 5–7% had evidence of early CKD as indicated by elevated cystatin C. Further, estimation of cystatin C using capillary blood samples (which are quick and simple to collect) correlated very closely with cystatin C measured in venous blood. A larger study to obtain population-based measures of cystatin C in patients with stage 1 or 2 CKD may identify a significant number of patients with pre-clinical CKD.
