Muscle mass normalization in the era of obesity: body mass ındex and weight-adjusted reference values for lumbar 3 vertebra skeletal muscle area.

BACKGROUND & AIMS: Height-adjusted indices (e.g., SMA/height²) may underestimate low muscle mass in overweight individuals. This study aimed to establish sex-specific body mass index (BMI)- and weight-adjusted reference values and cut-offs for total abdominal and psoas muscle indices from CT scans at the third lumbar vertebra (L3) in healthy adults.

METHODS

CT data of 482 young Turkish adults evaluated as living donor candidates (mean age 28.8 ± 5.9 y; 55.6% men) were analyzed. Total abdominal skeletal muscle area (TASMA) and psoas muscle area (PMA) were measured at the level of L3-vertebra and normalized to BMI to calculate the skeletal muscle index (TASMIBMI = TASMA/BMI [cm2/(kg/m2)]) and psoas muscle index (PMIBMI = PMA/BMI [cm2/(kg/m2)]), and alternatively to body weight (TASMIweight = TASMA/weight [cm2/kg]; PMIweight = PMA/weight [cm2/kg]). Sex-specific reference values were determined using the 5th percentile and mean minus 2 standard deviations (-2SD).

RESULTS

Using the 5th percentile approach with BMI-adjusted indices, cut-off values for low muscle mass were 4.87 (TASMIBMI) and 0.65 (PMIBMI) in men, and 3.24 (TASMIBMI) and 0.36 (PMIBMI) in women. Corresponding mean-2SD approach thresholds were 4.67 (TASMIBMI) and 0.55 (PMIBMI) in men, and 2.69 (TASMIBMI) and 0.25 (PMIBMI) in women. Weight-adjusted 5th percentile cut-off values for low muscle mass were 1.58 (TASMIweight) and 0.22 (PMIweight) in men, and 1.27 (TASMIweight) and 0.14 (PMIweight) in women. Corresponding mean-2SD thresholds were 1.49 (TASMIweight) and 0.18 (PMIweight) in men, and 1.10 (TASMIweight) and 0.11 (PMIweight) in women.

CONCLUSIONS

We report the first sex-specific BMI- and weight-adjusted SMA thresholds in a healthy Caucasian population. These reference values may improve sarcopenia screening across diverse body sizes. Future studies are required to examine whether low muscle mass defined by use of these thresholds are better associated with adverse consequences of low muscle mass/sarcopenia.