The Accuracy of Pre Bone Mineral Density FRAX Scores in Predicting Need for Treatment in Patients with Inflammatory Bowel Disease at Risk of Osteoporosis

Abstract

Purpose: Patients with Inflammatory Bowel disease (IBD) are at increased risk of Osteoporosis. Dual-Emission X-ray absorptiometry (DEXA) scans are frequently used to assess for osteoporosis and guide the need for preventative therapy. The WHO fracture risk assessment web tool can be used with or without bone mineral density (BMD) to calculate a FRAX score (10-year probability of major osteoporotic fracture and hip fracture). Patients are assigned, based on their pre-BMD FRAX outcome into low, intermediate (requiring BMD measurement) and high (requiring preventative therapy) risk groups in accordance with guidelines from the National Osteoporosis Guidelines Group (NOGG). Our study aimed to assess the accuracy of Pre-BMD FRAX scores in predicting need for preventative therapy in an IBD cohort. Methods: We conducted a retrospective review of 95 patients who had undergone an index DEXA scan whilst attending IBD clinics at our hospital between 2007 and 2011. Clinical data including demographics, disease characteristics and therapy were obtained from case note and electronic patient record review. Pre and post-BMD FRAX assessment scores were calculated retrospectively. All IBD patients were considered to have secondary osteoporosis as a risk factor for FRAX calculation. Fifteen patients were excluded as they had previously received bisphosphonates. Pre-BMD FRAX risk status was compared with Post-BMD FRAX outcome to identify patients requiring and not requiring therapy. Results: Eighty patients (female 56) with a median age of 53.8 and mean disease duration of 14.1 years were analysed. Fifty-two (65%) patients had Crohn's disease, 27 (34%) patients ulcerative colitis and 1 patient had IBD-type unclassified (IBDU). Pre-BMD FRAX risk status (low and intermediate/high risk) had a sensitivity of 100% (95% CI 87.9-100), in correctly identifying 28 out of 28 patients as needing treatment. Specificity was low at 31% (95% CI 19.9-44.3) identifying only 16 out of 52 patients as not needing treatment. The positive predictive value was low (44%; 95% CI 32.3-55.9) with 28 out of 64 patients correctly identified as needing treatment but the negative predictive value was high (100%; 95% CI 80.6-100) as all 16 patients were correctly identified as not needing treatment. Specificity and PPV results were influenced by the intermediate risk Pre-BMD FRAX sub-group of which 33 (73%) required lifestyle advice and 12 (27%) required preventative therapy following post-BMD FRAX assessment. Conclusion: In IBD patients, pre-BMD FRAX risk status is sensitive at predicting need for osteoporosis treatment and can help guide clinical decision making potentially avoiding DEXA scanning in IBD sub-groups.