Validation of the OSTA Index for Discriminating between High and Low Probability of Femoral Neck and Lumbar Spine Osteoporosis among Thai Postmenopausal Women
Sarayut Geater MD*, Rattana Leelawattana MD*, Alan Geater PhD**
Affiliation : * Department of Internal Medicine, Faculty of Medicine, Prince of Songkla University ** Epidemiology Unit, Faculty of Medicine, Prince of Songkla University
Rationale : Bone mineral density (BMD) measurement of postmenopausal women is needed to diagnose
osteoporosis. This is an expensive procedure and available in only a few hospitals in Thailand. The
Osteoporosis Self-Assessment Tool for Asians (OSTA) index, based on age and weight, has been developed for
screening of postmenopausal Asian women to identify women for whom there is little advantage in undergoing
bone densitometry. This index was developed for prediction of neck of the femur osteoporosis and did not
include spinal osteoporosis, which is also common. Furthermore, the index was based on data from a sample
of mainly ethnic Chinese. There is evidence that the BMD of Thai women is significantly higher for the same
age and weight than that of women of several other Asian ethnics, thus there is a need to validate the
appropriateness of the OSTA index for both femur and spinal osteoporosis among the Thai population.
Objective : To determine the properties of the OSTA index as a screening tool among postmenopausal women
in southern Thailand.
Patients : Three-hundred-and-eighty-eight postmenopausal women, with no history of disease or use of
drugs associated with secondary osteoporosis and no history of treatment for osteoporosis, attending the
postmenopausal clinic or internal medicine out-patient department of Songklanagarind Hospital, a teaching
hospital in southern Thailand, between November 2000 and April 2002.
Method : BMD t-scores of the neck of the femur and lumbar spine were collected retrospectively and a
diagnosis of osteoporosis made according to WHO criteria. Sensitivity and specificity and their 95% confidence
limits were calculated for the dichotomized OSTA index.
Results : Thirty-one percent of the women were detected as having osteoporosis, comprising neck of the femur
(12 percent) and lumbar spine (31 percent). Twenty nine women (7.5 percent) had evidence of spinal
fracture. The OSTA index at the standard cut-point of < -1 had a sensitivity and specificity of 0.93 (95% CI:
0.82 - 0.99) and 0.61 (95% CI: 0.56-0.66) respectively for neck of the femur but only 0.80 (95% CI: 0.72-0.87)
and 0.70 (95% CI: 0.64-0.75) respectively for lumbar spine. Raising the cut-point to < 0 reduced the high
false negative rate (0.20) in prediction of lumbar spine osteoporosis to 0.07 (95% CI: 0.03-0.13) and
identified 27 percent (95% CI: 23-32 percent) of all women at low risk of osteoporosis at either site. These
women may not need to undergo BMD measurement.
Conclusion : The standard cut-point of the OSTA index could identify most Thai postmenopausal women with
osteoporosis of the neck of the femur. However, to improve the sensitivity of detection of osteoporosis of the
lumbar spine, the cut-point of < 0 may be more appropriate.
Keywords : OSTA index, Thai postmenopausal women, Femoral neck, Lumbar spine, Osteoporosis
