title: Total-body skeletal muscle mass: evaluation of 24-h urinary creatinine excretion by computerized axial tomography.
abstract: A classic body-composition method is estimation of total-body skeletal muscle mass (SM, in kg) from 24-h urinary creatinine excretion (in g). Two approaches of unknown validity have been used to calculate SM from creatinine: one assumes a constant ratio of SM to creatinine, the so-called creatinine equivalence (k), and that SM = k x creatinine; the other suggests a highly variable ratio of SM to creatinine and is based on regression equations of the form SM = b + a x creatinine. We explored these two extreme possibilities by measuring SM with whole-body computerized axial tomography and collecting urinary creatinine during meat-free dietary conditions in 12 healthy adult men. Prediction equations were developed in the men that fit these two models: SM = 21.8 x creatinine (SD and CV of the ratio of SM to creatinine: 1.3 kg and 6.0%, respectively) and SM = 18.9 x creatinine + 4.1 (r = 0.92, P = 2.55 x 10(-5), SEE = 1.89 kg). The validity of each model is reviewed in the context of theoretical aspects of creatine-creatinine metabolism. This first investigation of the method of measuring urinary creatinine excretion to determine SM by using modern techniques raises important practical and basic questions related to SM prediction.
authors.affiliation: Department of Medicine, Obesity Research Center, New York, NY 10025, USA.
authors.forename: Z M
authors.initials: ZM
authors.lastname: Wang
authors.forename: D
authors.initials: D
authors.lastname: Gallagher
authors.forename: M E
authors.initials: ME
authors.lastname: Nelson
authors.forename: D E
authors.initials: DE
authors.lastname: Matthews
authors.forename: S B
authors.initials: SB
authors.lastname: Heymsfield
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology; D000328:Adult; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology*; D015331:Cohort Studies; D003401:Creatine / Q000378:metabolism; D003404:Creatinine / Q000378:metabolism / Q000652:urine*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000378:metabolism / Q000502:physiology; D014057:Tomography, X-Ray Computed
chemical_list: D003404:Creatinine; D003401:Creatine