[Cystatin C as a measure of glomerular filtration in patients with kidney transplants].

INTRODUCTION: Assessment of renal function is of great importance in clinical medicine, especially in renal transplant patients requiring frequent controls of renal function. Therefore, continuous efforts have been made in searching precise and simple method for determination of glomerular filtration rate (GFR). Serum level of cystatin C (CyC), protein of low molecular weight, has been proposed as measure of GFR, but the data of its value in renal transplant patients are scarce [8-10].

PURPOSE: The aim of this study was to compare the serum levels of low molecular weight proteins CyC and beta 2-microglobulin (beta 2-MG) with creatinine clearance, as well known measure of GFR, in renal transplant patients and control group of patients with different renal disease.

PATIENTS AND METHODS: The study included 36 patients divided into two groups. Group 1: 20 renal transplant patients (12 men and 8 women) aged between 22 and 63 (40.4 +/- 10.1) years with creatinine clearance from 7.1 to 77.7 ml/min. Group 2: 16 controls (5 men and 11 women) with various renal diseases, aged between 24 and 63 (41.5 +/- 12.5) years with creatinine clearance from 60.5 to 116.8 ml/min. N Latex Cystatin C and beta 2-microglobulin for the Behring Nephelometer System was used in this study. Creatinine was determined with Jaffe-reaction in serum and urine.

RESULTS: In renal transplant patients as well as in control group of patients the significant correlation between creatinine clearance and reciprocal values of the serum CyC (rt = 0.828; pt < 0.001; rc = 0.603; pc < 0.05) and reciprocal values of the serum beta 2-MG levels (rt = 0.791; pt < 0.001; rc = 0.627; pc < 0.05) was found (Graph 1). There was a slightly better correlation between creatinine clearance and reciprocal values of the serum CyC than the one between creatinine clearance and reciprocal values of the serum beta 2-MG without statistical significance in renal transplant patients. There was no difference in correlation coefficients between both low molecular weight proteins and creatinine clearance in Group 2. The correlation coefficient between serum CyC and beta 2-MG was r = 0.839 (p < 0.001) in renal transplant patients and r = 0.835 (p < 0.05) in control group. There were no significant differences in correlation coefficients between reciprocal values of serum CyC and creatinine clearance (p = 0.2043) as well as reciprocal values of serum beta 2-MG and creatinine clearance (p = 0.3717) between Group 1 and Group 2.

DISCUSSION: In renal transplant patients rapid assessment of graft function is necessary. This allows early recognition of rejection as well as differential diagnosis of different renal graft disorders. Study of Risch and co [16] suggested that serum CyC was very good marker for GFR in renal transplant patients which was confirmed by the other authors too [20-22]. During inflammatory process or other pathological conditions, especially during acute rejection or infections. CyC also provided precise assessment of GFR while creatinine clearance varied dramatically [16]. Serum concentration of beta 2-MG, another low molecular weight protein, also depends both on its production rate and the GFR [5, 19]. Its production is dramatically different in patients with infections [5] as well as while immunosuppressive drugs are used [16]. Therefore, beta 2-MG is impractical as GFR marker in patients with renal transplants. So, serum CyC was considered as better marker for GFR than beta 2-MG and creatinine clearance in renal transplant patients with different complications [16]. In this study serum CyC was slightly better marker for GFR than beta 2-MG, without statistical significance (Graph 1). Renal transplant patients, however, were in the stable condition at the time of the study.

CONCLUSION: Serum CyC was moderately better marker of GFR than beta 2-MG in renal transplant patients when they were in the stable condition. Serum CyC and beta 2-MG were the same markers of GFR in control group of patients with various renal diseases. There was no significant difference in correlation coefficients between reciprocal values of the serum CyC and creatinine clearance (p = 0.2043) as well as reciprocal values of the serum beta 2-MG levels and creatinine clearance (p = 0.3717) between two examined groups of patients. The studies on renal transplant patients with acute graft rejection or infections are warranted.