Inaccuracy of GFR predictions by plasma cystatin C in patients without kidney dysfunction and in advanced kidney disease.

Original artciel


Bakoush O, Grubb A, Rippe B.

Department of Nephrology and Department of Clinical Chemistry, University Hospital of Lund, Sweden

Clin Nephrol. 2008 May;69(5):331-8.


Background: In clinical practice there is need for a simple and reliable test for determination of impaired renal function. With reductions in GFR, the plasma cystatin C concentration (C, mg/l) will increase earlier than serum creatinine, and it is generally agreed that plasma cystatin C is only little affected by body weight, age or sex. However, some reports indicate that cystatin C may be influenced not only by GFR, but also by malignancy, inflammation and high doses of corticosteroids. The aim of the present study was to investigate how plasma cystatin C predicts GFR in distinct subcategories of patients with various disorders as well as in organ transplant patients. Methods: Plasma cystatin C was measured in 536 patients (age range 0.3 – 96 years, 262 females, 274 males), consecutively referred to our hospital for determination of GFR by iohexol clearance. Correlations of log GFR vs. log cystatin C were used to compare plasma cystatin C and measured GFR for the following categories: individuals with no known kidney disease (No-KD), malignant patients with (mostly) normal GFR, solid organ-transplanted patients, and patients with native chronic kidney disease (CKD). Results: In patients with normal kidney function and cystatin C level <= 1 mg/l, the cystatin C was poorly correlated with GFR (R2 = 0.13). By contrast, in patients with chronic kidney disease (log) plasma cystatin C was highly correlated with (log) GFR (R2 = 0.87). This correlation was more or less unchanged whether the cause of the reduction in GFR was CKD at Stages 1 – 3 (90 > GFR > 30 ml/min–1 (1.73 m2)–1) or solid organ transplantation (GFR = 84.55 C1.7666 and GFR = 83.95 C–1.5968, respectively). Conclusion: Therefore, for these categories, a common equation for all patients with increased cystatin C, irrespective of cause of renal impairment, could be used, namely that presented by Grubb et al. [2005] (GFR = 83.93 C–1.676). However, at marked reductions of renal function (GFR < 30 or cystatin C > 2), i.e. for CKD Stages 4 and 5, the Grubb prediction equation is less accurate. Based on our data, we suggest the equation GFR = 50.52 C–1.26 for this category of patients.

Keywords: Inaccuracy of GFR predictions by plasma cystatin C in patients without kidney dysfunction and in advanced kidney disease