Abstract
A pilot study of 107 women aged 60–69 years recently suggested that the measurement of broadband ultrasound attenuation (BUA) provides a superior cost effective pre-screen referral method for bone mineral density (BMD) measurement by DXA (dual-energy X-ray absorptiometry) than can be achieved by clinical criteria (CC). The aim of this study was to compare the accuracy and cost effectiveness of BUA and clinical criteria in a younger cohort. 599 women aged 50–54 years (52.18 ± 1.35) had previously been measured by DXA at lumbar spine and right femoral neck, along with BUA measurement of the right calcaneus. Each subject had also completed an extensive clinical and social questionnaire to ascertain those who would have met one or more of the six general clinical criteria adopted by our Centre. Each subject was classified by DXA using the WHO criteria as normal, osteopenic or osteoporotic, defined at lumbar spine or femoral neck. Sensitivity, specificity and accuracy were calculated for BUA and the clinical criteria, noting that analysis was undertaken with and without the oestrogen deficiency clinical criterion (CC1): “Any oestrogen deficient woman who would want to be treated or would want to continue treatment if found to be osteopenic or osteoporotic”. The accuracy for identifying osteoporotic subjects was 72.8% for BUA (at the point of matched sensitivity and specificity, 75 dB MHz−1), 30.7% for CC(1–6) and 64.3% for CC(2–6). When osteopenic subjects were incorporated, the accuracies were 63.8% for BUA (at the point of matched sensitivity and specificity, 82 dB MHz−1), 60.3% for CC(1–6) and 55.7% for CC(2–6). The minimum cost per osteoporotic subject correctly identified was £573.50 by DXA alone, £325 by BUA, £458 by CC(1–6) and £416 by CC(2–6). When osteopenic subjects were incorporated, the costs were £87, £83.50, £78 and £74, respectively. The overall cost, dependent upon the prevalence of osteoporosis (or osteopenia) within the population, more accurately indicates the feasibility of a population-based screening programme. For the identification of either osteoporotic or osteopenic subjects from the general population by DXA, the prevalence-compensated cost (cost per subject correctly identified multiplied by prevalence) is £45, irrespective of age cohort. If CC(2–6) were adopted for the identification of osteoporotic subjects alone, the prevalence-compensated cost would be £32 and £42 for the 50–54 and 60–69 aged cohorts, respectively. For BUA, the prevalence-compensated cost falls to £25 and £43 for the 50–54 and 60–69 aged cohorts, respectively. If osteoporotic or osteopenic subjects were to be identified in the 50–54 aged cohort, both CC(2–6) (£38) and BUA (£43) perform similarly to DXA alone.
BUA appears to provide a valuable population pre-screen for the identification of osteoporotic subjects, less so for osteopenic. It is suggested that if both osteopenic and osteoporotic women are to be identified for clinical management incorporating DXA, then neither BUA nor clinical criteria are satisfactory referral methods. An unanswered question from this study, however, is whether ultrasound has an independent role in the assessment of fracture risk for perimenopausal women who do not have the benefit of referral for DXA.