title: Low serum creatinine is associated with type 2 diabetes in morbidly obese women and men: a cross-sectional study.
abstract: BACKGROUND
  Low skeletal muscle mass is associated with insulin resistance and metabolic syndrome. Serum creatinine may serve as a surrogate marker of muscle mass, and a possible relationship between low serum creatinine and type 2 diabetes has recently been demonstrated. We aimed to validate this finding in a population of Caucasian morbidly obese subjects.
  
  
  METHODS
  Cross-sectional study of 1,017 consecutive morbidly obese patients with an estimated glomerular filtration rate >60 ml/min/1.73 m2. Logistic regression (univariate and multiple) was used to assess the association between serum creatinine and prevalent type 2 diabetes, including statistically testing for the possibility of non-linearity in the relationship by implementation of Generalized Additive Models (GAM) and piecewise linear regression. Possible confounding variables such as age, family history of diabetes, waist-to-hip ratio, hypertension, current smoking, serum magnesium, albuminuria and insulin resistance (log HOMA-IR) were adjusted for in three separate multiple logistic regression models.
  
  
  RESULTS
  The unadjusted GAM analysis suggested a piecewise linear relationship between serum creatinine and diabetes. Each 1 mumol/l increase in serum creatinine was associated with 6% (95% CI; 3%-8%) and 7% (95% CI; 2%-13%) lower odds of diabetes below serum creatinine levels of 69 and 72 mumol/l in women and men, respectively. Above these breakpoints the serum creatinine concentrations did not reduce the odds further. Adjustments for non-modifiable and modifiable risk factors left the piecewise effect for both women and men largely unchanged. In the fully adjusted model, which includes serum magnesium, albuminuria and log HOMA-IR, the piecewise effect for men was statistically non-significant, but it remained present for women. Patients with creatinine levels below median had approximately 50% (women) and 75% (men) increased odds of diabetes.
  
  
  CONCLUSIONS
  Low serum creatinine is a predictor of type 2 diabetes in Caucasian morbidly obese patients, independent of age, gender, family history of diabetes, anthropometric measures, hypertension, and current smoking. Longitudinal studies of both obese and non-obese populations are needed to investigate whether serum creatinine may be causally linked with type 2 diabetes, and if so, precisely how they are linked.
authors.affiliation: The Morbid Obesity Centre, Vestfold Hospital Trust, Tønsberg, Norway. joran@online.no.
authors.forename: Jøran
authors.initials: J
authors.lastname: Hjelmesæth
authors.forename: Jo
authors.initials: J
authors.lastname: Røislien
authors.forename: Njord
authors.initials: N
authors.lastname: Nordstrand
authors.forename: Dag
authors.initials: D
authors.lastname: Hofsø
authors.forename: Helle
authors.initials: H
authors.lastname: Hager
authors.forename: Anders
authors.initials: A
authors.lastname: Hartmann
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