DXA-Derived Indices in the Characterisation of Sarcopenia

Abstract

Sarcopenia is linked with increased risk of falls, osteoporosis and mortality. No consensus exists about a gold standard "dual-energy X-ray absorptiometry (DXA) index for muscle mass determination" in sarcopenia diagnosis. Thus, many indices exist, but data on sarcopenia diagnosis agreement are scarce. Regarding sarcopenia diagnosis reliability, the impact of influencing factors on sarcopenia prevalence, diagnosis agreement and reliability are almost completely missing. For nine DXA-derived muscle mass indices, we aimed to evaluate sarcopenia prevalence, diagnosis agreement and diagnosis reliability, and investigate the effects of underlying parameters, presence or type of adjustment and cut-off values on all three outcomes. The indices were analysed in the BioPersMed cohort (58 ± 9 years), including 1022 asymptomatic subjects at moderate cardiovascular risk. DXA data from 792 baselines and 684 follow-up measurements (for diagnosis agreement and reliability determination) were available. Depending on the index and cut-off values, sarcopenia prevalence varied from 0.6 to 36.3%. Height-adjusted parameters, independent of underlying parameters, showed a relatively high level of diagnosis agreement, whereas unadjusted and adjusted indices showed low diagnosis agreement. The adjustment type defines which individuals are recognised as sarcopenic in terms of BMI and sex. The investigated indices showed comparable diagnosis reliability in follow-up examinations.

Keywords: BioPersMed cohort; DXA; DXA-derived muscle mass indices.

Figure 1

Allocations of indices to adjustment or baseline parameter for calculation. DXA: dual-energy X-ray absorptiometry; ASM: appendicular skeletal muscle mass; AMMI: appendicular skeletal muscle mass index; TSMI: total skeletal mass index; LESMI: lower extremity skeletal muscle mass index; SMI: skeletal muscle mass index; ALMI: appendicular lean mass index; Min: reference values Minnesota; NM: reference values New Mexico; rLMABC: relative lean mass (20th percentile ABC Health study); rLM20: relative lean mass (20th percentile).

Figure 2

Comparability of sarcopenia diagnosis by use of different DXA-derived indices. SMI, LESMI, rLM20, AMMI, TSMI, ALMI NM and ASM were used in this figure since rLM20 included rLMABC identified sarcopenic persons and ALMI Min in ALMI NM. Each square shows the total numbers of individuals recognised as sarcopenic by the two compared indices (percentage in brackets). The shade of grey indicates the range of overlap as a percentage between the diagnoses of sarcopenia by the two compared indices. The shades range from 0 to 20% accordance (light grey) in steps of 20 percent each up to 81 to 100% accordance (dark grey). DXA: dual-energy X-ray absorptiometry; SMI: skeletal muscle mass index; ASM: appendicular skeletal muscle mass; AMMI: appendicular skeletal muscle mass index; ALMI: appendicular lean mass index; NM: reference values New Mexico; TSMI: total skeletal mass index; LESMI: lower extremity skeletal muscle mass index; rLM20: relative lean mass (20th percentile).

Figure 3

Comparison of the numbers of sarcopenic individuals identified by skeletal muscle mass based indices. Each partial circle depicts an index. The arrows show the compared indices. The darker the arrow, the more indices are compared. The number in the arrows indicate the numbers of individuals identified as sarcopenic by the compared indices. SMI: skeletal muscle mass index; AMMI: appendicular skeletal muscle mass index; TSMI: total skeletal mass index; LESMI: lower extremity skeletal muscle mass index.

Figure 4

Comparison of the number of sarcopenic individuals identified by ASM-based indices and ASM. Each partial circle depicts an index or ASM. The number in the partial circles indicates the number of individuals recognised as sarcopenic per index. The black numbers reaching over two differently coloured partial circles represent the number of individuals recognised by the two compared parameters. The striped area shows the number of persons identified as sarcopenic, according to all three compared parameters. TSMI: total skeletal mass index; AMMI: appendicular skeletal muscle mass index; ASM: appendicular skeletal muscle mass.

Figure 5

Factors significantly influencing the diagnosis of sarcopenia by each index in our binary logistic regression model. Full lines mark significant associations, dashed lines associations by trend. ASM: appendicular skeletal muscle mass; AMMI: appendicular skeletal muscle mass index; ALMI: appendicular lean mass index; NM: reference values New Mexico; TSMI: total skeletal mass index; LESMI: lower extremity skeletal muscle mass index; rLM20: relative lean mass (20th percentile); SMI: skeletal muscle mass index; PTH: parathyroid hormone; VK: vitamin K; BMI: body mass index. VD: 25-hydroxyvitamin D₃.