人工透析患者の身体組成と死亡率

人工透析患者の身体組成代理マーカーによる死亡率予測に関する論文を紹介します。 人工透析患者のObesity Paradoxを説明できる論文です。

Kamyar Kalantar-Zadeh, Elani Streja, Miklos Z. Molnar, Lilia R. Lukowsky, Mahesh Krishnan, Csaba P. Kovesdy and Sander Greenland: Mortality Prediction by Surrogates of Body Composition: An Examination of the Obesity Paradox in Hemodialysis Patients Using Composite Ranking Score Analysis. Am. J. Epidemiol. (2012) doi: 10.1093/aje/kwr384 First published online: March 16, 2012

人工透析患者の死亡率と、dry weight（透析後体重）と血清クレアチニン値（筋肉量の代理マーカー）の変化との関連を、121,762人のコホートから後ろ向きに調査しています。

結果ですが、低体重、低筋肉量、体重減少、血清クレアチニン低下を認める場合、死亡率は高かったです。また、「体重減少・血清クレアチニン増加」した患者は、「体重増加・血清クレアチニン低下」した患者より、死亡率は低かったです。

これより体重減少より血清クレアチニン低下のほうがより強い死亡の予測因子といえます。人工透析患者のObesity Paradoxは、筋肉量減少の程度で説明できる可能性があるとしています。つまり、BMIに関わらず筋肉量が多い患者ほど死亡率が低くなるといえます。

Obesity Paradoxの論文はたくさんありますが、筋肉量である程度説明できるという論文は初めて見た気がします。人工透析患者（と腎機能正常の方）では血清クレアチニン値が筋肉量のマーカーであり、この数値と変化をみることで、一定の予後予測ができるかもしれませんね。

Abstract
In hemodialysis patients, lower body mass index and weight loss have been associated with higher mortality rates, a phenomenon sometimes called the obesity paradox. This apparent paradox might be explained by loss of muscle mass. The authors thus examined the relation to mortality of changes in dry weight and changes in serum creatinine levels (a muscle-mass surrogate) in a cohort of 121,762 hemodialysis patients who were followed for up to 5 years (2001–2006). In addition to conventional regression analyses, the authors conducted a ranking analysis of joint effects in which the sums and differences of the percentiles of change for the 2 measures in each patient were used as the regressors. Concordant with previous body mass index observations, lower body mass, lower muscle mass, weight loss, and serum creatinine decline were associated with higher death rates. Among patients with a discordant change, persons whose weight declined but whose serum creatinine levels increased had lower death rates than did those whose weight increased but whose serum creatinine level declined. A decline in serum creatinine appeared to be a stronger predictor of mortality than did weight loss. Assuming residual selection bias and confounding were not large, the present results suggest that a considerable proportion of the obesity paradox in dialysis patients might be explained by the amount of decline in muscle mass.