Effect of large weight reductions on measured and estimated kidney function.
When patients experience large weight loss, muscle mass may be affected followed by changes in plasma creatinine (pCr). The MDRD and CKD-EPI equations for estimated GFR (eGFR) include pCr. We hypothesised that a large weight loss reduces muscle mass and pCr causing increase in eGFR (creatinine-based equations), whereas measured GFR (mGFR) and cystatin C-based eGFR would be unaffected if adjusted for body surface area.



Prospective, intervention study including 19 patients. All attended a baseline visit before gastric bypass surgery followed by a visit six months post-surgery. mGFR was assessed during four hours plasma51Cr-EDTA clearance. GFR was estimated by four equations (MDRD, CKD-EPI-pCr, CKD-EPI-cysC and CKD-EPI-pCr-cysC). DXA-scans were performed at baseline and six months post-surgery to measure changes in lean limb mass, as a surrogate for muscle mass.



Patients were (mean ± SD) 40.0 ± 9.3 years, 14 (74%) were female and 5 (26%) had type 2 diabetes, baseline weight was 128 ± 19 kg, body mass index 41 ± 6 kg/m2 and absolute mGFR 122 ± 24 ml/min. Six months post-surgery weight loss was 27 (95% CI: 23; 30) kg, mGFR decreased by 9 (-17; -2) from 122 ± 24 to 113 ± 21 ml/min (p = 0.024), but corrected for current body surface area (BSA) mGFR was unchanged by 2 (-5; 9) ml/min/1.73 m2(p = 0.52). CKD-EPI-pCr increased by 12 (6; 17) and MDRD by 13 (8; 18) (p < 0.001 for both), while CKD-EPI-cysC was unchanged by 2 (-8; 4) ml/min/1.73 m2(p = 0.51). Lean limb mass was reduced by 3.5 (-4.4;-2.6; p < 0.001) kg and change in lean limb mass correlated with change in plasma creatinine (R2= 0.28, p = 0.032).



Major weight reductions are associated with a reduction in absolute mGFR, which may reflect resolution of glomerular hyperfiltration, while mGFR adjusted for body surface area was unchanged. Estimates of GFR based on creatinine overestimate renal function likely due to changes in muscle mass, whereas cystatin C based estimates are unaffected.



ClinicalTrials.gov, NCT02138565 . Date of registration: March 24, 2014.
Steno Diabetes Center Copenhagen, Niels Steensens Vej 1, 2820, Gentofte, Denmark. bvon0013@regionh.dk.
Bernt Johan
BJ
von Scholten
Steno Diabetes Center Copenhagen, Niels Steensens Vej 1, 2820, Gentofte, Denmark.
Frederik
F
Persson
Hvidovre University Hospital, Hvidovre, Denmark.
Maria S
MS
Svane
Steno Diabetes Center Copenhagen, Niels Steensens Vej 1, 2820, Gentofte, Denmark.
Tine W
TW
Hansen
Hvidovre University Hospital, Hvidovre, Denmark.
Sten
S
Madsbad
Steno Diabetes Center Copenhagen, Niels Steensens Vej 1, 2820, Gentofte, Denmark.|University of Copenhagen, Copenhagen, Denmark.|Aarhus University, Aarhus, Denmark.
Peter
P
Rossing
D015502:Absorptiometry, Photon; D000328:Adult; D001823:Body Composition; D001830:Body Surface Area; D002860:Chromium Radioisotopes; D003404:Creatinine / Q000378:metabolism*; D055316:Cystatin C / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000378:metabolism; D004492:Edetic Acid; D005260:Female; D015390:Gastric Bypass; D005919:Glomerular Filtration Rate; D006801:Humans; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000378:metabolism*; D009767:Obesity, Morbid / Q000150:complications / Q000378:metabolism / Q000601:surgery*; D011446:Prospective Studies; D015431:Weight Loss
D002860:Chromium Radioisotopes; D055316:Cystatin C; D004492:Edetic Acid; C000615375:Chromium-51; D003404:Creatinine
Bariatric surgery; Creatinine; Cystatin C, DXA scan; Glomerular filtration rate; Muscle mass