Osteoporosis self-reports unreliable measure for case defintions

By Ingrid Grasmo

Self-reports of incident osteoporosis in middle-aged and older women should not be relied on for a case definition, suggest study findings showing poor-to-moderate validity for this measure.

The clinical diagnosis of osteoporosis is based on bone densitometry and bone mineral density (BMD) measurements, but it is not always feasible to expose all study participants to these tests. Indeed, case definitions of osteoporosis in large-scale epidemiological studies and national health surveys often rely on self-report of diagnosis, medication, or fractures.

"The validity of self-reported osteoporosis is often questioned, but validation studies are lacking," say Geeske Peeters (University of Queensland, Brisbane, Australia) and colleagues.

Using participant data from the Australian Longitudinal Study on Women's Health, the researchers compared self-reported diagnosis with medication information from self-report and pharmaceutical reimbursement claims from 17,627 middle-aged (56-61 years in 2007) and 9588 older (79-84 years in 2005) women.

Concurrent validity of self-report was examined by calculating agreement, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). Construct validity was tested through examination of association of self-reported diagnosis with osteoporosis-related characteristics such as fracture, weight, body pain, back pain, and physical function.

Analysis of concurrent validity of self-reported diagnosis for prevalent osteoporosis among middle-aged women showed a high percentage agreement for Pharmaceutical Benefits Scheme (PBS) prescription reimbursement claims (95.7%) followed by self-reported medication (95.3%). Both measures showed good sensitivity (73.8% and 78.6%), specificity (96.4% and 95.7%), and NPV (99.1% and 99.5%).

Similar findings for prevalent osteoporosis were seen among older women, although the agreement was slightly lower for PBS claims (87.1%) and self-reported claims (86.5%). In contrast to mid-age women, PPV was better among older women for both self-reported medication (57.1% vs 29.9%) and PBS prescriptions (79.5% vs 42.0%).

When the researchers analyzed the concurrent validity for incident osteoporosis, they found that sensitivity and PPV were lower relative to those seen for prevalent osteoporosis, with agreement, specificity, and NPV remaining comparably high for both middle-aged and older women.

Significant associations were found between self-reported diagnosis and all five osteoporosis-related characteristics for prevalent osteoporosis, and for three out of five characteristics in middle-aged women and four out of five characteristics in older women for incident osteoporosis.

The researchers note that a major limitation of the study was the lack of bone densitometry for diagnosis of osteoporosis.

The findings are published in the journal Osteoporosis International.

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