The International Society for Clinical Densitometry (ISCD) recommends that change in bone mineral density (BMD) only be considered significant when it exceeds the 95% least significant change (LSC) derived from that facility's precision study1. The lumbar spine is often affected by structural artifact such that not all four lumbar vertebrae are evaluable. A review published for the 2023 ISCD Position Development Conference (PDC) found that using fewer than 4 vertebrae reduces precision and increases the LSC. This deterioration in spine precision is inversely related to the number of evaluable vertebrae, such that ISCD recommends against reporting spine BMD based on a single vertebra2. It was proposed that each dual-energy x-ray absorptiometry (DXA) facility calculate the LSC for L1-4 and for specific combinations of 2 and 3 vertebrae2. A site-matched LSC should then be used to determine significant change in spine BMD when using fewer than 4 vertebrae.

Given that spine BMD precision worsens as fewer vertebrae are included, the question arises as to whether spine BMD based on fewer than 4 vertebrae is as responsive as L1-4 for detecting a significant increase in BMD on treatment and a significant decrease without treatment. The current study was undertaken to compare treatment-concordant changes in spine BMD (i.e., significant increase in BMD with high exposure to anti-resorptive treatment versus significant decrease without treatment) according to different numbers and combinations of lumbar vertebrae using site-matched LSC values. The study conducted using the population-based DXA registry from Manitoba, Canada, and precision assessments across more than 25 years representing a variety of scanner configurations.