Relationship between biochemical parameters and glomerular filtration rate by Cockcroft-Gault, CKD EPI and cystatin C in patients with type 1 diabetes

Abstract

Annotation. The aim of research is to study correlations of biochemical parameters with glomerular filtration rate according to Cockcroft-Gault, CKD EPI and cystatin C in patients with type 1 diabetes (T1D). 78 men and 62 women aged 22-26 years with T1D were examined. The control group consisted of 8 almost healthy men and 13 almost healthy women of the same age. The level of microalbuminuria and cystatin C was determined in all patients by enzyme-linked immunosorbent assay. Biochemical evaluation of fasting blood glucose, glucose 2 h after exercise, mean value of glucose, creatinine, GFR according to Cockcroft-Gault, CKD EPI and GFR according to cystatin C. Correlation analysis between the series of indicators was calculated using Spearman statistics in the license package “Statistica 5.5”. In patients with T1D, there is no significant correlation in normoalbuminuria between urinary albumin levels and GFR by Cockcroft-Gault (in women), CKD EPI and cystatin C (in all study groups). No significant correlations were found between urinary albumin levels and GFR by Cockcroft-Gault, CKD EPI and cystatin C in the proteinuria group. The correlation analysis revealed in the general group and in women with proteinuria an association between the average value of blood glucose and low GFR levels by Cockcroft-Gault, CKD EPI (negative medium strength correlation r = from -0.31 to -0.46) and elevated creatinine (positive strong correlation r=0.62 and r=0.91), indicating an unfavorable role of hyperglycemia in the development of nephropathy in patients with T1D. Higher correlations of cystatin C with GFR by cystatin C (r= -1.0) than by creatinine with GFR by Cockcroft-Gault (r = from - 0.63 to 0.99) and by CKD EPI (r = from -0.73 to -0.99) were demonstrated. The strength of the correlations increases from GFR by Cockcroft-Gault to GFR by cystatin C. Correlations between creatinine and GFR by Cockcroft-Gault and CKD EPI were characterized by sex differences (greater in women) and an increase in their strength synchronously with an increase in urinary microalbumin. At the same time, there is a consistently high identical value (r= -1.0) of correlations of the level of cystatin C with GFR on cystatin C in all comparison groups. Neither the sex factor nor the degree of albuminuria affected the change in their strength. Only men with microalbuminuria had moderate feedback between creatinine and cystatin C (r= -0.46). In all groups of women, in the general group and in men with normoalbuminuria and proteinuria, the correlations are close to zero, which may indicate the absence of a linear relationship between these indicators. When dividing the sample according to the level of cystatin C between the level of creatinine and the level of cystatin C, the following were found: medium feedback (r= -0.37) in the general group with normoalbuminuria and cystatin C>0.9; moderate feedback (r= -0.37) in the general group and in men with proteinuria and cystatin C<0.9 strong feedback (r= -0.90 and r= -0.88). Thus, in the course of correlation analysis it was found: microalbuminuria is not an independent marker of diabetic nephropathy (DN), starting from preclinical and ending with a clinically manifested stage of this complication; for timely and adequate diagnosis of DN it is necessary to measure the level of albumin, creatinine and cystatin C, which are independent markers of renal dysfunction; cystatin C gives a more accurate approximation to the actual values of GFR than creatinine; cystatin C is more sensitive in the early stages, and creatinine is a marker of later stages of DN development; hyperglycemia is the main initiating metabolic factor in the development and progression of DN.