The use of calcaneal stiffness index to screen for osteoporosis in HIV-infected individuals

Charlotte Walker, HIV i-Base

Chelsea and Westminster Hospital reported results on the feasibility of using calcaneal stiffness as an indicator for osteoporosis in HIV-positive patients. [1]

Currently, a DEXA scan remains the gold standard measure of Bone Mineral Density (BMD) with a T-score of -1 and above being normal -1 to -2.5 indicating osteopaenia and <-2.5 indicating osteoperosis. However, DEXA scans are not available in all clinics, require extra patient attendance and radiation safety approval and cost around £60.

Several studies have previously shown a significant difference in BMD and fracture prevalence in both HIV-positive men and women. A population-based study by Triant et al. reported a high level of significance (p=0.0001 in men and p=0.002 in women) in bone fractures between over 2,200,000 HIV-negative patients and 8,525 HIV-positive patients. [2]

Scourfield et al at Chelsea and Westminster Hospital have found that a calcaneal ultrasound test using the GE-Achilles Insight machine is able to calculate the calcaneal stiffness index (CSI) and estimate the t-score. In HIV-negative people, CSI is currently used to predict hip fracture risk and vertebral fracture in post-menopausal women. However, this is not yet used in HIV-positive people.

The test is portable, takes 15 seconds to perform with minimal inter-operator variability. Osteopenia is most readily apparent in parts of the skeleton with high bone turnover as found in highly trabeculated, weight-bearing bones. The calcaneus (heel bone) is ideal as it is easily accessible, comfortable for the patient and weight-bearing.

The study aimed to correlate CSI with DEXA scan results in an HIV-positive population to assess the value and cost-effectiveness of using the GE-Achilles Insight machine as a screen tool for osteoperosis.

CSI measurements using the GE-Achilles Insight were performed on 100 people at random who had undergone a DEXA scan within the last 6 months. Their median age was 51 years (IRQ: 46-58), 85% were male, positive for a median of 15 years (IQR: 11-20) and with a BMI of 24 (IQR 21-26). Ethnicity of participants was 83% white Caucasian, 10% black African, 4% SE Asian, 1% black Caribbean, 1% Middle Eastern and 1% Indian. CSI scores were analysed to determine the optimum sensitivity. A cost-effectiveness analysis was then conducted.

The DEXA scan showed a prevalence of 15% osteoporosis and 55% osteopaenia. The CSI t-score showed 67% positive (estimated t-score =<-1.0) and 43% negative (estimated t-score >-1.0). This meant in the CSI t-score had 100% sensitivity but only 51% specificity compared to the DEXA scan. The positive predictive value of a CSI score of =<-2.5 for osteoporosis was 30%.

The cost-effectiveness analysis concluded that CSI is reliable and cost-effective method. If the 100 study participants involved in this study who had all previously undergone the DEXA scan had been screened first with CSI using a cut-off value of =<-1.0 this would have resulted in all cases of osteoporosis identified and 43 fewer DEXA scans which amounts to a saving of £2,795 (at an average cost of £65 per scan). However, due to the lower level of specificity, this would also have meant that 19 cases of osteopenia were missed.

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The cost of the GE-Achilles Insight is only £12,000 and for a minimal investment the considerable ongoing concerns of high levels of currently undiagnosed bone disease could be easily addressed in every large clinic.

EACS guidelines recommend repeat DEXA screening every 3-5 years in patients at higher risk of BMD and include HIV as a risk factor when using the FRAX calculator and age over 50 years as a risk factor if not using FRAX. The financial and health saving appear significant given aging positive population.

CSI t-scores are also quicker, easier and less inconvenient for the patient. Patient volunteers or staff without medical training can also perform these to reduce cost further.

References:

A Scourfield et al. The use of calcaneal stiffness index to screen for osteoporosis in HIV-infected individuals. 17th Annual BHIVA Conference, 68 April 2011, Bournemouth. Oral abstract O33.
Triant VA et al. Fracture prevalence among human immunodeficiency virus (HIV)-infected versus non-HIV-infected patients in a large U.S. healthcare system. J Clin Endocrinol Metab 2008;93:3499-3504.
European AIDS Clinical Society (EACS). Guidelines: Prevention and Management of Non-infectious Co-morbidities in HIV.
http://www.europeanaidsclinicalsociety.org/guidelinespdf/2_Non_Infectious_Co_Morbidities_in_HIV.pdf