The measured glomerular filtration rate (mGFR) before and 6 months after bariatric surgery: A pilot study.
BACKGROUND
Over the last few decades, the prevalence of obesity has increased dramatically. This increase has been mirrored by a rise in the risk of a number of health conditions, including hypertension, diabetes and chronic kidney disease. Although the weight loss following bariatric surgery has been shown to relieve the severity of diabetes and reduce hypertension, the effect on renal function has been less extensively evaluated.


OBJECTIVE
The aims of the present study were to: (i) compare the estimated glomerular filtration rate (eGFR, using the MDRD and CKD-EPI equations) and the calculated glomerular filtration rate (using the 24-hour urine volume) with the measured glomerular filtration rate (mGFR) assessed with the plasma iohexol clearance method in severely obese patients, and (ii) evaluate the effect of weight loss on the mGFR 6 months after bariatric surgery.


METHODS
Before and six months after bariatric surgery (Roux-en-Y gastric bypass or sleeve gastrectomy), eligible patients for bariatric surgery were admitted as day cases to the nephrology unit, where they underwent a plasma iohexol clearance test. The GFR was also estimated using the MDRD and CKDEPI equations and the 24-hour urine method. Changes in eGFR and mGFR were compared using a Wilcoxon test for paired data.


RESULTS
Data from 16 patients with severe obesity (mean ± standard deviation of Body Mass Index [BMI]: 43.9 ± 7.3 kg/m2) were analyzed. At baseline, 12 (75%) presented with hypertension and 10 (63%) presented with diabetes. The median [range] iohexol clearance rate was 109 [57-194] mL/min. The plasma iohexol clearance test evidenced hyperfiltration (mGFR>120 mL/min) in 7 patients. In contrast, the eGFR values generated by the MDRD equation, the CKDEPI equation and the GFR MFR calculated with the 24-hour urine method only identified hyperfiltration in 1, 0 and 5 patients, respectively. Six months after surgery, the mean BMI had fallen significantly (P<0.0012), and the severity of diabetes (according to the HbA1clevel) had decreased significantly from 6.6 [6.0-9.8] % to 5.7 [5.2-8.6] % (P=0.025). The iohexol clearance rate increased slightly after bariatric surgery. Changes in BMI after surgery do not seem to be correlated with the changes in iohexol clearance. In patients displaying hyperfiltration at baseline, the mGFR fell significantly (n=7; P=0.01) and returned to near normal values. No significant changes in the eGFR were observed.


CONCLUSIONS
Our results suggest that MDRD and CKD-EPI equations do not provide accurate estimates of the true GFR in severely obese patients (particularly in those with hyperfiltration). Iohexol clearance or other methods for determining mGFR should constitute the gold standard for the accurate evaluation of renal function in this context. Renal function (as evaluated by the mGFR) improved 6 months after bariatric surgery in severely obese individuals particularly in patients displaying hyperfiltration at baseline. However, these observations must be confirmed in a larger study with a longer follow-up period.
Nephrology Unit, Ambroise-Paré Hospital, AP-HP, université de Versailles Saint-Quentin-en-Yvelines, 9, avenue Charles-de-Gaulle, 92104 Boulogne-Billancourt cedex, France.
Maëva
M
Clerte
Inserm U1018, université de Versailles Saint-Quentin en Yvelines, université Paris-Saclay, 94800 Villejuif, France; FCRIN INI-CRCT, 54500 Nancy, France.
Sandra
S
Wagner
Department of nutrition, Georges-Pompidou European Hospital, AP-HP, 75015 Paris, France.
Claire
C
Carette
Inserm U1018, université de Versailles Saint-Quentin en Yvelines, université Paris-Saclay, 94800 Villejuif, France.
Albane
A
Brodin-Sartorius
Nephrology Unit, Ambroise-Paré Hospital, AP-HP, université de Versailles Saint-Quentin-en-Yvelines, 9, avenue Charles-de-Gaulle, 92104 Boulogne-Billancourt cedex, France; Inserm U1018, université de Versailles Saint-Quentin en Yvelines, université Paris-Saclay, 94800 Villejuif, France.
Éve
É
Vilaine
Inserm U-1173, department of pharmacology and toxicology, Raymond-Poincaré Hospital, AP-HP, université de Versailles Saint-Quentin en Yvelines, 92380 Garches, France.
Jean-Claude
JC
Alvarez
Inserm U-1173, department of pharmacology and toxicology, Raymond-Poincaré Hospital, AP-HP, université de Versailles Saint-Quentin en Yvelines, 92380 Garches, France.
Emuri
E
Abe
Department of nutrition, Georges-Pompidou European Hospital, AP-HP, 75015 Paris, France.
Charles
C
Barsamian
Department of nutrition, Georges-Pompidou European Hospital, AP-HP, 75015 Paris, France; Université Paris 5 René Descartes, 75006 Paris, France.
Sébastien
S
Czernichow
Nephrology Unit, Ambroise-Paré Hospital, AP-HP, université de Versailles Saint-Quentin-en-Yvelines, 9, avenue Charles-de-Gaulle, 92104 Boulogne-Billancourt cedex, France; Inserm U1018, université de Versailles Saint-Quentin en Yvelines, université Paris-Saclay, 94800 Villejuif, France; FCRIN INI-CRCT, 54500 Nancy, France. Electronic address: ziad.massy@aphp.fr.
Ziad A
ZA
Massy
D000328:Adult; D050110:Bariatric Surgery / Q000379:methods; D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D003404:Creatinine / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000150:complications; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D006973:Hypertension / Q000150:complications; D007472:Iohexol / Q000032:analysis; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000150:complications / Q000601:surgery*; D010865:Pilot Projects; D011182:Postoperative Care; D011237:Predictive Value of Tests; D011300:Preoperative Care; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000150:complications / Q000175:diagnosis*; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D015431:Weight Loss
D015415:Biomarkers; D007472:Iohexol; D003404:Creatinine
Bariatric surgery; Glomerular filtration rate; Iohexol; Obesity