osteoporosis – Investigations
The reduced bone mass and risk of fracture can be measured by a simple, non-invasive test called BMD (bone mineral density) test or bone densitometry. As per recommendations of the National Osteoporosis Foundation (USA), BMD test may be advised:
- For females above 65 years of age
- For postmenopausal females below 65 years of age if one or more risk factors are present
- For postmenopausal females having fracture
- If the test is going to help in deciding initiation of therapy for osteoporosis.
II. Detection of Osteoporosis can be done by:
- Bone density measurements (Bone densitometry): Osteoporosis can be detected at an early stage with the help of Bone densitometry or BMD tests. It can be done by:
- SPA (single photon absorptiometry)
- DPA (dual photon absorptiometry)
- DEXA (dual energy x-ray absorptiometry)
- QCT (quantitative computed tomography)
Bone mineral density is expressed in terms of T score and/or Z score. T score is number of standard deviation above or below average peak bone mass of young adults where as Z score is number of standard deviation above or below average peak bone mass of age matched controls. T score less than 1 SD below average peak BMD is considered to be normal whereas, between 1-2.5 SD below average peak BMD suggests Osteopenia (low bone mass). T score more than 2.5 SD below average peak BMD indicates Osteoporosis.
- X-ray: Osteoporosis can be detected by X-ray but only in advance cases when approximately 30-40% of bone mass is lost. X-ray spine may show decreased bone density, loss of horizontal trabeculations, biconcave vertebral bodies, ‘codfish’ vertebrae and compression fractures. X-ray pelvis may show demineralization of femoral neck and head.
III. Monitoring of Osteoporosis can be done by estimation of:
- Serum bone specific alkaline phosphatase and osteocalcin.
- Urinary excretion of hydroxyproline and pyridinolines (free and total).
IV. Other investigations that may be advised include:
- Serum calcium, inorganic phosphorus and alkaline phosphatase.
- Serum levels of thyroid hormone, parathyroid hormone, estrogen or testosterone to exclude the causes of secondary osteoporosis