Efficacy of cystatin C as a screening test for reduced glomerular filtration rate

ABSTRACT

The objective of this study was to evaluate the efficacy of cystatin C as a screening test for reduced glomerular filtration rate [GFR] in comparison to S. creatinine and to assess whether cystatin C is performed differentially in either glomerular or tubular renal diseases or not. This study involved 105 patients with different renal diseases they were admitted as inpatients in Internal Medicine Department at Ain Shams University Hospital, and were classified according to GFR ml/min/1.73 m[2] into group I patients, n = 35, GFR >/= 70 ml/min/1.73 m[2] group II patients, n = 33, GFR [< 70 - >/= 50] ml/mins/1.73m[2] and group III patients, n= 37, GFR < 50ml/min/1.73m[2], and a control group of 30 volunteers with matched age and sex to evaluate the reference value of cystatin C. All groups were subjected to the following complete history taking and thorough clinical examination. Kidney function tests including Bun, S. creatinine, creatinine clearance, 24 hours urinary proteins quantitation, [99m]Tc DTPA renal isotope scanning for accurate evaluation of glomerular filtration rate [GFR]. Abdominal U/S with full comment on the kidneys. Qualitative assessment of urinary proteins. Assessment of serum cystatin C by DAKO cystatin C pet kit which is particle enhanced turbidimetric immunassay. Our results revealed that the mean S. cystatin C was 7.9 +/- 3.8, 14.3 +/- 8.2 and 16.2 +/- 3.6 mg/l in groups I, II and III respectively when compared with that of the control group with a mean of 0.9 +/- 1 mg/l it was statically highly significant [F = 61.8, P < 0.01]. S. cystatin C was more sensitive than S. creatinine in reflecting the true GFR, this was specially observed in group I patients [mild renal impairment] as their mean serum creatinine was still within its normal range 0.97 +/- 0.4 mg/dl, while their mean GFR measured by both creatinine clearance and isotope clearance was 68.3 +/- 4.7, 67.5 +/- 45 ml/min/1.73 m[2] respectively. Meanwhile, their mean S. cystatin C was 7.9 +/- 3.8 mg/l statistically highly significant than that of the control group with a mean of 0.9 +/- 1 mg/l, [P < 0.05]. Also there was statistically non significant correlation between S. cystatin C and S. creatinine in group I patients [r = 0.1, P > 0.05] while there was significant correlation between them in group II and III patients [r = 0.38, 0.59, P < 0.05]. Moreover, S. cystatin C has a significant negative correlation with GFR measured by both creatinine clearance [r = -0.37, -0.54 and -0.48] and radioisotope clearance [r = -0.34, -0.35 and -0.37], [P < 0.05] in groups I, II and III respectively, i.e., throughout the whole range of renal impairment. Cystatin C had non significant correlation with either age or sex of the patients. While, S. creatinine had a significant correlation with creatinine clearance and isotope clearance in group II and III patients, i.e., with advanced renal diseases, but not with group I patients [mild renal impairment]. Also S. cystatin C had higher sensitivity [90% [vs] 83%] and negative predictive value [NPV] [89 [vs] 80] than S. creatinine in assessing GFR measured by both creatinine clearance or by radioisotope clearance. There was non significant difference regarding the mean S. cystatin C between subgroup [A] [glomerular diseases] and subgroup [B] [tubular diseases] within the same GFR category [P > 0.05]. S. cystatin C was more sensitive and superior to S. creatinine in detecting reduced GFR measured by both creatinine and radioisotope clearance. S. cystatin C is more efficacious than S. creatinine as a screening test as it had a higher sensitivity and higher negative predictive values than S. creatinine. In detecting reduced GFR. The efficacy of cystatin C is independent on either glomerular or tubular renal diseases and showed a high degree of reproducibility