Urinary creatinine-skeletal muscle mass method: a prediction equation based on computerized axial tomography

Area of Science:

• Human Physiology
• Biochemistry
• Body Composition Analysis

Background:

• Estimating total body skeletal muscle mass (SM) from 24-hour urinary creatinine excretion (Cr) is a classic method.
• Two primary prediction equation types exist: one assuming a constant SM/Cr ratio and another assuming a variable ratio.

Purpose of the Study:

• To explore the validity of two extreme possibilities for SM/Cr ratio in prediction equations.
• To develop and compare prediction equations for SM based on Cr excretion using modern measurement techniques.

Main Methods:

• Skeletal muscle mass (SM) was measured using whole-body computerized axial tomography (CT).
• 24-hour urinary creatinine excretion (Cr) was collected under meat-free dietary conditions.
• Prediction equations were developed and validated in 12 healthy young men.

Main Results:

• A constant SM/Cr ratio equation (SM = 21.8 x Cr) showed a low standard deviation (1.3 kg) and coefficient of variation (6.0%) for the SM/Cr ratio.
• A variable SM/Cr ratio equation (SM = 18.9 x Cr + 4.1) demonstrated high correlation (r = 0.92, p = 2.55 x 10(-5)) and a standard error of estimate (SEE) of 1.9 kg.
• This study is the first to investigate the Cr-SM method using modern CT for quantifying total body SM.

Conclusions:

• The study provides a comparative analysis of two distinct models for estimating skeletal muscle mass from urinary creatinine.
• The findings suggest that a constant SM/Cr ratio model may offer a reliable approach for body composition assessment in specific populations.
• Further review of each model's validity is recommended for clinical and research applications.