Glomerular filtration rate estimation using cystatin C alone or combined with creatinine as a confirmatory test.
BACKGROUND
Glomerular filtration rate (GFR) estimating equations using the combination of creatinine and cystatin C (eGFRcr-cys) are more accurate than equations using either alone (eGFRcr or eGFRcys). New guidelines suggest measuring cystatin C as a confirmatory test when eGFRcr may be inaccurate, but do not specify demographic or clinical conditions in which eGFRcys or eGFRcr-cys are more accurate than eGFRcr nor which estimate to use in such circumstances.


METHODS
We compared the performance of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations in 1119 subjects in the CKD-EPI cystatin C external validation dataset. Subgroups were defined by eGFRcr, age, sex, diabetes status and body mass index (BMI). The reference test was GFR measured using urinary or plasma clearance of exogenous filtration markers. Cystatin C and creatinine assays were traceable to primary reference materials. Accuracy was defined as the absolute difference in eGFR compared with mGFR.


RESULTS
The mean mGFR was 70 ± 41 (SD) mL/min/1.73 m(2). eGFRcys was more accurate than eGFRcr at lower BMI and less accurate at higher BMI, especially at higher levels of eGFRcr. There were small differences in accuracy in people according to the diabetes status. eGFRcr-cys was as accurate or more accurate than eGFRcr or eGFRcys in these and all other subgroups.


CONCLUSIONS
eGFRcr-cys, but not eGFRcys, is more accurate than eGFRcr in most subgroups we studied, suggesting preferential use of eGFRcr-cys when serum cystatin C is measured as a confirmatory test to obtain more accurate eGFR. Further studies are necessary to evaluate diagnostic strategies for using eGFRcys and eGFRcr-cys.
Division of Nephrology, Tufts Medical Center, Boston, MA, USA.
Li
L
Fan
Division of Nephrology, Tufts Medical Center, Boston, MA, USA.
Lesley A
LA
Inker
Global Clinical Development, Amgen, Thousand Oaks, CA, USA.
Jerome
J
Rossert
INSERM, CESP Centre for Research in Epidemiology and Population Health, U1018, Epidemiology of Diabetes, Obesity, and Chronic Kidney Diseases Team, Villejuif 94807, France.
Marc
M
Froissart
Steno Diabetes Center, Gentofte, Denmark.
Peter
P
Rossing
Department of Pediatrics, Medical School, University of Minnesota, Minneapolis, MN, USA.
Michael
M
Mauer
Division of Nephrology, Tufts Medical Center, Boston, MA, USA.
Andrew S
AS
Levey
D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood*; D003920:Diabetes Mellitus / Q000378:metabolism; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007677:Kidney Function Tests / Q000592:standards; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000503:physiopathology*
D015415:Biomarkers; D055316:Cystatin C; D003404:Creatinine
CKD-EPI; cystatin C; diagnostic test accuracy; estimated GFR