Cystatin C and collagen type IV in diagnostics of chronic kidney disease in type 2 diabetic patients

Aim. To compare kidney disease markers: glomerular filtration rate (GFR), calculated upon creatinine and cystatin C, urinary cystatin C, collagen type IV and albumin in type 2 diabetic patients with normal and moderately reduced renal function. Materials and methods. 56 patients, aged 43?70 years, and 16 healthy controls, aged 40-72 years, were included in the study. GFR was calculated by equations based on creatinine (CKD-EPIcreat), cystatin C (CKD-EPIcys) or both markers (CKD-EPIcreat-cys). Serum and urinary cystatin C was measured by immunoturbidimetric method, urinary albumin, albumin excretion rate (AER) and collagen type IV excretion was determined by ELISA. The body composition was investigated in 24 patients by dual-energy X-ray absorptiometry. Results. In diabetic patients serum cystatin C level correlated positively with age (r=0.37), GFR calculated by CKD-EPIcreat (r=-0.43) and fat mass percentage (r=0.55). There was a positive correlation between GFR calculated by the CKD-EPIcys and GFR by CKD-EPIcreat (r=0.48). In multiple regression analysis the percentage of body fat influenced the GFR calculated by CKD-EPIcys or CKD-EPIcreat-cys. No correlation between urinary cystatin C and serum cystatin C level, GFR and AER was found. Collagen type IV excretion was increased in patients with decreased GFR, compared to those with normal GFR (p=0.002). Urinary collagen type IV correlated with both GFR and AER (r=-0.28 and r=0.47). Conclusion. The measurement of serum cystatin C with calculation of GFR by CKD-EPIcys and CKD-EPIcreat-cys, in addition to the CKD-EPIcreat, increases the accuracy of CKD diagnostics in type 2 diabetic patients. However, obesity and particularly body fat mass affect the results of estimation of GFR based on cystatin C. The increase in urinary collagen type IV, but not in cystatin C excretion, is related to GFR decline and AER elevation in these patients.