Novel Algorithm to Estimate Fat-Free Muscle Volumes in Women Using the Urinary Deuterated-Creatine Dilution Method

Muscle mass declines after menopause and is a key risk factor for frailty, falls and poor physical function as women age. The deuterated creatine (D₃Cr) dilution method provides a direct assessment of muscle mass, but its accuracy in Asian women has not been evaluated. Our aim was to develop a new D₃Cr algorithm incorporating anthropomorphic variables that can estimate fat-free muscle mass, using magnetic resonance imaging (MRI) as the reference standard.

The Integrated Women's Health Programme (IWHP) enrolled 1201 healthy community-dwelling women, aged 45-69 years at baseline, who attended gynaecological clinics from 2014 to 2016. Between February 2021 and July 2023, 894 participants were recontacted, and 451 of the respondents agreed to ingest 30 mg of D₃Cr and had available MRI measurements of fat-free thigh and erector spinae volumes. Urinary levels of creatine, creatinine and D₃-creatinine levels were measured by tandem mass spectrometry 4 days after ingestion of D₃Cr. Muscle mass was estimated using the two D₃Cr algorithms (D₃Cr_original and D₃Cr_modified) in current use and a newly developed algorithm (D₃Cr_Ht-Wt) incorporating anthropometric variables that estimate fat-free muscle volumes. Pearson's correlation analyses were used to compare the performances of the D₃Cr algorithms with MRI. Bland-Altman analysis was used to ascertain agreement between D₃Cr_Ht-Wt and MRI.

Participants (n = 451, mean age 62.6 ± 5.9) were randomly divided into training (n = 367) and validation (n = 84) cohorts. In the training cohort, stepwise multivariable regression modelling indicated that age (β = -0.011, p = 0.076) and ethnicity (β = 0.154, p = 0.317 [Indian]; β = -0.012, p = 0.942 [Malay] compared to Chinese) were not associated with fat-free muscle volumes. In the final model, D₃Cr-determined creatine pool size (β = 0.032, p < 0.001), body weight (β = 0.030, p < 0.001) and height (β = 4.336, p < 0.001) were independently associated with fat-free muscle volumes and were incorporated into a new algorithm (D₃Cr_Ht-Wt). In a separate validation cohort, muscle volumes estimated using the D₃Cr_Ht-Wt algorithm (R = 0.813) had a higher correlation with MRI-measured fat-free muscle volumes than both D₃Cr_original (R = 0.672) and D₃Cr_modified (R = 0.692) algorithms. Bland-Altman analysis indicated a low bias of 0.112 L and limits of agreement of -0.969 L to +1.190 L.

Muscle volumes estimated with the D₃Cr_Ht-Wt algorithm had high correlation and agreement with MRI-measured fat-free muscle volumes. The convenience of the D₃Cr method for participants suggests its potential to be a clinically relevant method for assessing fat-free muscle volumes in sarcopenia studies.