Inaccuracy of GFR predictions by plasma cystatin C in patients without kidney dysfunction and in advanced kidney disease.
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 <or= 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 C(1.7666) and GFR=83.95(C-1.5968), respectively).


CONCLUSIONS
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.
Bakoush
O
O
Department of Nephrology, University Hospital of Lund, Sweden. Omran.Bakoush@med.lu.se
Grubb
A
A
Rippe
B
B
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D002648:Child; D002675:Child, Preschool; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007223:Infant; D007472:Iohexol; D007674:Kidney Diseases / Q000097:blood / Q000175:diagnosis / Q000503:physiopathology*; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D019737:Transplants
D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D007472:Iohexol