Cockcroft-Gault式によるクレアチニンクリアランス(Ccr)の誤算

Using The Cockcroft-Gault Equation, The Creatinine Clearance(Ccr)Could Not Represent The Glomerular Filtration Rate(GFR)

要旨　これまで慢性腎臓病(chronic kidney disease;CKD)の指標として推算糸球体濾過量(estimated glomerular filtration rate;eGFR)が定着してきた．一方，日本循環器学会は非弁膜症性心房細動(non-valvular atrial fibrillation;NVAF)の治療において，新規経口抗凝固薬(novel oral anticoagulant;NOAC)使用時はCockcroft-Gault(CG)式によるクレアチニンクリアランス(creatinine clearance;Ccr)を腎機能の指標として用いることを発表した．しかし，これは「太るほど腎機能を過大評価する」式であり，今日の肥満時代には不適切と考える．さらにCcrとeGFRの誤差をシュミレーションして調べたところ，多くの場合にCcr(CG式)はGFRを過大評価して，CKDの重症度分類を誤判定する危険があることがわかった．またeGFRも日本人成人男性の標準体型(170cm/63kg/1.73m²)を想定した簡易式であるため，各患者の体格(身長・体重)からDu Bois式によって体表面積(body surface area;BSA)を計算して体格補正し，より正確にGFRを推算する必要がある．そして生命を左右するNOAC使用時のガイドラインは早急に再検討を要する．

　The estimated glomerular filtration rate(eGFR)has been established as an index of chronic kidney disease(CKD). But the Japanese Circulation Society(JCS)recently announced that, for patients receiving novel oral anticoagulants(NOACs)to treat non-valvular atrial fibrillation(NVAF), creatinine clearance(Ccr)predicted by the Cockcroft-Gault(CG)equation should be used as the index of renal function. However, this equation has a tendency to overestimate renal function in overweight patients. Thus, it is considered inappropriate to use the equation in people with obesity-related health problems today. In addition, the results of simulation to examine errors in the Ccr and eGFR showed that the Ccr(using the CG equation)overestimated the glomerular filtration rate(GFR)in many cases, which has led to misjudgment of the classification and staging of CKD. Meanwhile, the eGFR is a simple equation based on the standard body constitution of Japanese adult men(170cm/63kg/1.73m²). For more accurate GFR, it is necessary to calculate body surface area(BSA)based on each patient's body size(height and weight)using the Du Bois formula. Thus, guidelines for patients with NVAF on NOAC therapy must immediately and carefully be reviewed.