Accuracy of GFR estimation in obese patients.
OBJECTIVE
Adequate estimation of renal function in obese patients is essential for the classification of patients in CKD category as well as the dose adjustment of drugs. However, the body size descriptor for GFR indexation is still debatable, and formulas are not validated in patients with extreme variations of weight.


METHODS
This study included 209 stages 1-5 CKD obese patients referred to the Department of Renal Function Study at the University Hospital in Lyon between 2010 and 2013 because of suspected renal dysfunction. GFR was estimated with the Chronic Kidney Disease and Epidemiology equation (CKD-EPI) and measured with a gold standard method (inulin or iohexol) not indexed (mGFR) or indexed to body surface area determined by the Dubois and Dubois formula with either real (mGFRr) or ideal (mGFRi) body weight. Mean bias (eGFR-mGFR), precision, and accuracy of mGFR were compared with the results obtained for nonobese participants (body mass index between 18.5 and 24.9) who had a GFR measurement during the same period of time.


RESULTS
Mean mGFRr (51.6 ± 24.2 ml/min per 1.73 m(2)) was significantly lower than mGFR, mGFRi, and eGFRCKD-EPI. eGFRCKD-EPI had less bias with mGFR (0.29; -1.7 to 2.3) and mGFRi (-1.62; -3.1 to 0.45) compared with mGFRr (8.7; 7 to 10). This result was confirmed with better accuracy for the whole cohort (78% for mGFR, 84% for mGFRi, and 72% for mGFRr) and participants with CKD stages 3-5. Moreover, the Bland Altman plot showed better agreement between mGFR and eGFRCKD-EPI. The bias between eGFRCKD-EPI and mGFRr was greater in obese than nonobese participants (8.7 versus 0.58, P<0.001).


CONCLUSIONS
This study shows that, in obese CKD patients, the performance of eGFRCKD-EPI is good for GFR ≤ 60 ml/min per 1.73 m(2). Indexation of mGFR with body surface area using ideal body weight gives less bias than mGFR scaled with body surface area using real body weight.
Departments of Renal Function Study and, †Nephrology, Edouard Herriot Hospital, Hospices Civils de Lyon, Lyon, France;, ‡Institut National de la Santé et de la Recherche Médicale U1060, Laboratoire de Recherche en Cardiovasculaire, Métabolisme, Diabétologie et Nutrition, Lyon, France;, §University of Lyon, Université Lyon 1 Claude Bernard, Lyon, France, ‖Unité Mixte de Recherche 5305 Centre National de la Recherche Scientifique, Université Claude Bernard, Lyon, France.
Sandrine
S
Lemoine
Fitsum
F
Guebre-Egziabher
Florence
F
Sens
Marie-Sophie
MS
Nguyen-Tu
Laurent
L
Juillard
Laurence
L
Dubourg
Aoumeur
A
Hadj-Aissa
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D001830:Body Surface Area; D001835:Body Weight; D003287:Contrast Media; D005260:Female; D005602:France; D005919:Glomerular Filtration Rate; D006785:Hospitals, University; D006801:Humans; D007444:Inulin; D007472:Iohexol; D007668:Kidney / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009765:Obesity / Q000150:complications* / Q000175:diagnosis; D011237:Predictive Value of Tests; D051436:Renal Insufficiency, Chronic / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D012720:Severity of Illness Index; D055815:Young Adult
D003287:Contrast Media; D007472:Iohexol; D007444:Inulin