Estimating GFR among participants in the Chronic Renal Insufficiency Cohort (CRIC) Study.
BACKGROUND
Glomerular filtration rate (GFR) is considered the best measure of kidney function, but repeated assessment is not feasible in most research studies.


METHODS
Cross-sectional study of 1,433 participants in the Chronic Renal Insufficiency Cohort (CRIC) Study (ie, the GFR subcohort) to derive an internal GFR estimating equation using a split-sample approach.


METHODS
Adults from 7 US metropolitan areas with mild to moderate chronic kidney disease; 48% had diabetes and 37% were black.


METHODS
CRIC GFR estimating equation.


METHODS
Urinary (125)I-iothalamate clearance testing (measured GFR [mGFR]).


METHODS
Laboratory measures, including serum creatinine and cystatin C, and anthropometrics.


RESULTS
In the validation data set, the model that included serum creatinine level, serum cystatin C level, age, sex, and race was the most parsimonious and similarly predictive of mGFR compared with a model additionally including bioelectrical impedance analysis phase angle, CRIC clinical center, and 24-hour urinary creatinine excretion. Specifically, root mean square errors for the separate models were 0.207 versus 0.202, respectively. Performance of the CRIC GFR estimating equation was most accurate for the subgroups of younger participants, men, nonblacks, non-Hispanics, those without diabetes, those with body mass index <30 kg/m(2), those with higher 24-hour urine creatinine excretion, those with lower high-sensitivity C-reactive protein levels, and those with higher mGFRs.


CONCLUSIONS
Urinary clearance of (125)I-iothalamate is an imperfect measure of true GFR; cystatin C level is not standardized to certified reference material; lack of external validation; small sample sizes limit analyses of subgroup-specific predictors.


CONCLUSIONS
The CRIC GFR estimating equation predicts mGFR accurately in the CRIC cohort using serum creatinine and cystatin C levels, age, sex, and race. Its performance was best in younger and healthier participants.
Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA. andersah@mail.med.upenn.edu
Amanda Hyre
AH
Anderson
Wei
W
Yang
Chi-yuan
CY
Hsu
Marshall M
MM
Joffe
Mary B
MB
Leonard
Dawei
D
Xie
Jing
J
Chen
Tom
T
Greene
Bernard G
BG
Jaar
Patricia
P
Kao
John W
JW
Kusek
J Richard
JR
Landis
James P
JP
Lash
Raymond R
RR
Townsend
Matthew R
MR
Weir
Harold I
HI
Feldman
D000328:Adult; D000368:Aged; D002097:C-Reactive Protein / Q000032:analysis; D003404:Creatinine / Q000097:blood / Q000652:urine; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D051436:Renal Insufficiency, Chronic / Q000175:diagnosis / Q000503:physiopathology*
D055316:Cystatin C; D002097:C-Reactive Protein; D003404:Creatinine