Precision of estimating equations for GFR in children with a solitary functioning kidney: the KIMONO study.
OBJECTIVE
Children with a solitary functioning kidney may develop CKD. Although widely used, equations to estimate GFR are not validated in these patients. This study sought to determine the precision of common estimating equations in the KIMONO (KIdney of MONofunctional Origin) cohort.


METHODS
Two creatinine-based (estimated GFR [eGFR]-Schwartz, urinary creatinine clearance), two cystatin C-based (eGFR-Zappitelli1, eGFR-CKiD [Chronic Kidney Disease in Children] 1), and two cystatin C/creatinine-based (eGFR-Zappitelli2, eGFR-CKiD2) estimates were compared with the gold standard GFR measured by inulin single injection (GFR-inulin) in 77 children with a solitary functioning kidney (time span of assembly, 2005-2012). Included patients were 1.5-19.8 years of age. Kidney Disease Outcomes Quality Initiative (K/DOQI) classification was compared between GFR-inulin and eGFR methods to analyze misclassification by estimating equations.


RESULTS
The eGFR-CKiD2 equation performed best in children with a solitary functioning kidney (mean bias, -0.9 ml/min per 1.73 m(2); 95% and 54% of values within ±30% and ±10% of GFR-inulin, respectively). Mean bias for eGFR-Schwartz was 0.4 ml/min per 1.73 m(2), with 90% and 33% of values within ±30% and ±10% of GFR-inulin, respectively. For all estimates, misclassification in K/DOQI stage ranged from 22% (eGFR-Zappitelli1) to 44% (urinary creatinine clearance) of children.


CONCLUSIONS
Use of a combined serum cystatin C/creatinine-based equation (eGFR-CKiD2) is recommended to monitor renal function in children with a solitary functioning kidney. When cystatin C is not routinely available, eGFR-Schwartz should be used. Misclassification in K/DOQI-stage remains a caveat for all equations.
Department of Pediatric Nephrology, VU University Medical Center, Amsterdam, The Netherlands. r.westland@vumc.nl
Rik
R
Westland
Yael
Y
Abraham
Arend
A
Bökenkamp
Birgit
B
Stoffel-Wagner
Michiel F
MF
Schreuder
Joanna A E
JA
van Wijk
D000293:Adolescent; D000367:Age Factors; D015415:Biomarkers / Q000097:blood / Q000652:urine; D002648:Child; D003404:Creatinine / Q000097:blood / Q000652:urine; D055316:Cystatin C / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007444:Inulin; D007668:Kidney / Q000503:physiopathology*; D008297:Male; D008954:Models, Biological; D011237:Predictive Value of Tests; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology / Q000652:urine
D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D007444:Inulin; D003404:Creatinine