Generation of a new cystatin C-based estimating equation for glomerular filtration rate by use of 7 assays standardized to the international calibrator.
BACKGROUND
Many different cystatin C-based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays.


METHODS
Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C-based equation for estimation of GFR.


RESULTS
We developed a simple cystatin C-based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, [Formula: see text] is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C.


CONCLUSIONS
A virtually assay-independent simple cystatin C-based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced.
Department of Clinical Chemistry, Laboratory Medicine, University Hospital, Lund, Sweden; anders.grubb@med.lu.se.
Anders
A
Grubb
Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Suita, Osaka, Japan;
Masaru
M
Horio
Department of Medical Sciences, Uppsala University, Uppsala, Sweden;
Lars-Olof
LO
Hansson
Department of Occupational and Environmental Medicine, Lund University, Lund, Sweden;
Jonas
J
Björk
Department of Radiology, Central Hospital, Kristianstad, University of Lund, Sweden;
Ulf
U
Nyman
Department of Medical Sciences, Uppsala University, Uppsala, Sweden;
Mats
M
Flodin
Department of Medical Sciences, Uppsala University, Uppsala, Sweden;
Anders
A
Larsson
Department of Pediatric Nephrology, VU University Medical Center, Amsterdam, The Netherlands;
Arend
A
Bökenkamp
Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Suita, Osaka, Japan;
Yoshinari
Y
Yasuda
Department of Pediatric Nephrology, VU University Medical Center, Amsterdam, The Netherlands;
Hester
H
Blufpand
Department of Clinical Chemistry, Laboratory Medicine, University Hospital, Lund, Sweden;
Veronica
V
Lindström
Institute for Reference Materials and Measurements, Joint Research Centre, European Commission, Geel, Belgium;
Ingrid
I
Zegers
Siemens Healthcare Diagnostics Products GmbH, Marburg, Germany;
Harald
H
Althaus
Department of Clinical Chemistry, Laboratory Medicine, University Hospital, Lund, Sweden;
Søren
S
Blirup-Jensen
Department of Laboratory Medicine, EIJU, General Hospital, Tokyo, Japan;
Yoshi
Y
Itoh
Department of Medicine, Örebro University Hospital, Örebro, Sweden;
Per
P
Sjöström
Equalis, Uppsala, Sweden;
Gunnar
G
Nordin
Department of Nephrology and Transplantation, Skåne University Hospital, Lund, Sweden;
Anders
A
Christensson
Roche Diagnostics GmbH, Penzberg, Germany;
Horst
H
Klima
Gentian Technology AS, Moss, Norway;
Kathrin
K
Sunde
Dako Denmark A/S, Glostrup, Denmark;
Per
P
Hjort-Christensen
Abbott Diagnostics, Lake Forest, IL;
David
D
Armbruster
Sentinel CH. SpA, Milan, Italy.
Carlo
C
Ferrero
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D044466:Asian People; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D002138:Calibration; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D055316:Cystatin C / Q000097:blood* / Q000592:standards; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007118:Immunoassay / Q000592:standards; D007223:Infant; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry / Q000592:standards; D012015:Reference Standards; D012016:Reference Values; D012737:Sex Factors; D044465:White People; D055815:Young Adult
D015415:Biomarkers; D055316:Cystatin C