The Estimation of Glomerular Filtration Rate Based on the Serum Cystatin C and Creatinine Values

Renal insufficiency is one of the most serious renal diseases. Early diagnosis plays an essential role. Serum creatinine as a marker has had priority so far. The use of cystatin C for estimation of glomerular filtration rate has been recommended recently. There is a set of formulae which consolidates serum values of both creatinine and cystatin C. The study focuses on different formulae and their estimation for the purpose of better, faster, and more accurate diagnosis of renal insufficiency.

The sample consists of 75 examinees which are divided into three groups. The first group is made of patients with the glomerular filtration rate (GFR) 90 - 120 mL/minute/1.73m². The second group consists of patients with GFR 60 - 89 mL/minute/1.73m² and the third with GFR 30 - 59 mL/minute/1.73m². The exclusion criteria are the following: children and adolescents under the age of 20, pregnant women, patients on corticosteroid therapy and blockers of the distal tubular creatinine secretion. The five equations (GFR1-5) used in this research are: a Cockcroft-Gault equation - GFR1; a MDRD equation - GFR2; CKD-EPI - an equation based on cystatin C - GFR3; CKD-EPI - an equation based on cystatin C, adjusted according to the gender and age - GFR4; and CKDEPI - a combined equation based on cystatin C and creatitine, adjusted according to the age, gender, and race - GFR5. Upon acquiring the results, it is followed up with the statistical data analysis followed by graphs and tables.

After data analysis, it is established that data distribution does not show normal distribution in each case, which leads to the use of nonparametric statistics. Depending on the stage of kidney injury there are different results regarding the difference in statistics of the used formulae. The highest sensitivity is recorded with the formulae GFR4 and GFR5. Then the increase in cystatin C levels increases sensitivity with the formulae GFR3 and GFR4.

As a result of this study, it is to be established that the formula of choice is the GFR3 - CKD-EPI formula based on serum cystatin C values, without adjustments. Its sensitivity, specificity, price, and feasibility are to be observed as parameters. Besides that, the increase in serum cystatin levels leads to the increase of sensitivity of the GFR3 formula, which could be an additional factor in the selection of formulae.