by Michele F. Bellantoni, M.D
The current standard for assessing bone mass is dual energy x-ray absorptiometry, or DEXA. Measurement of the bone mass of the lumbar spine and hip are currently used for diagnostic purposes and monitoring of treatment. Peripheral sites such as wrist and heel can be useful screening tools in older individuals; however there is discordance between bone sites in rates of loss with aging. Thus, many newly postmenopausal women will have a normal bone mass of the heel, and yet have clinical significant low bone mass of the spine. The FDA recently approved ultrasound techniques for use as a screening test for low bone mass.(ref 14) Currently, the different manufacturers of bone densitometers all use different reference populations from which the standard deviations from normal are calculated, also called T scores. There are differences in calibration between companies as well, so that an individual patients bone density reading can differ by as much as 12% from one machine to the next. Thus, to monitor a patients response to treatment, the same bone densitometer must be used. This is a challenge when patients are often referred to centers based on insurance coverage.
While the T score is used to assess bone mass, diagnose osteoporosis, and predict fracture risk, the Z score, or comparison with age-matched individuals is used to determine whether the patients bone mass is unexpectedly low. A Z score of -2.0 or more negative is often used to determine whether a more extensive laboratory assessment is done to assess for secondary causes of bone loss such as myeloma, vitamin D deficiency, and hyperparathyroidism.
A bone density study provides information on the patients current bone mass, but does not assess whether bone loss is accelerated. Blood and urine studies have been developed to assess bone turnover. Most of these markers are breakdown products of proteins specific to bone, including n-telopeptide (NTX or Osteomark®), C-telopeptide (CTX) and deoxypyridinoline crosslinks (Pyrilinks-D®). The appropriate use of these markers in clinical practice is controversial.(ref 15) There are data to show that they predict bone loss as assessed by bone densitometry over one to two years. Small studies show potential use to monitor response to treatments such as bisphosphonates and estrogen. Studies are repeated three months after treatment with a clinical response assessed at three months. The variablity in measurements is estimated at 20%; a decrease in value of 30% is considered a treatment response. Effective October 1, 1999, Medicare will provide reimbursement for biomarkers to monitor bone loss, at costs of roughly $30 per study.
Medicare Guidelines for Bone Densitometry
Medicare Guidelines for bone densitometry became effective 7/1/98.(ref 16)
Patients must meet one of the following criteria:
- Estrogen deficient woman at clinical risk for osteoporosis (the clinician can refer a postmenopausal woman who is receiving hormone replacement if there is concern that the therapy may not be preventing bone loss)
- Vertebral abnormalities as demonstrated by x-ray to be indicative of osteoporosis, osteopenia, or vertebral fracture.
- Chronic glucocorticoid use; defined as 7.5 mg/day or greater of prednisone or equivalent steroid for 3 months or greater, or anticipated use of such therapy.
- Primary hyper-parathyroidism
- Individual being monitored to assess the response to, or efficacy of, an FDA-approved osteoporosis drug therapy.
**Medicare will cover a bone mass measurement for a beneficiary once every two years.
**More frequent central bone densitometry will be covered if medically necessary such as with steroid use, or to confirm the findings of a screening study such as ultrasound or peripheral bone densitometry.
**The National Osteoporosis Foundation also suggests that bone densitometry is appropriate in the setting of positive family history of osteoporosis, chronic thyroxine use, height loss, vertebral deformity without x-ray confirmation, and any fracture for which the degree of trauma is disproportionate to the degree of injury.(ref 1)
Medicare reimbursement for central bone densitometry is roughly $140; peripheral and ultrasound studies are reimbursed at approximately $50. It is now possible for patients to receive peripheral densitometry at locations such as pharmacies and health fairs. Again, because bone mass at peripheral sites changes more slowly with time, and there is discordance in bone mass between different anatomical sites, a normal peripheral bone mass measurement in a patient with significant risk factors for osteoporosis should be screened with a bone mass measurement of the spine and hip. The peripheral ultrasound technologies are accurate, but there is insufficient data to access precision over time. Thus they are not currently used to monitor response to treatment, although this recommendation may change with more data.(ref 17)
SCORE Screening Quiz
Located below is a six question screening questionnaire for osteoporosis, SCORE (Simple Calculated Osteoporosis Risk Estimation). SCORE has been shown to have 89% sensitivity and 50% specificity in an ambulatory population of postmenopausal women.(ref 18) The questionnaire below can be used by office support staff to identify individuals for whom bone densitometry is warranted to confirm the clinical suspicion of osteoporosis.
|1. What is your current age in years? ____|
|Enter the number in redhere.______|
|2. What is your race or ethnic group?|
|If African-American/Black American, enter 0. For all other groups, enter 5 here.______|
|3. Have your ever been treated for or told you have rheumatoid arthritis?|
|If yes, enter 4If no, enter 0 ______|
|4. Since the age of 45, have you experienced a fracture (broken bone) at any of the following sites?|
|Hip: If yes, enter 4; If no, enter 0 ______Rib: If yes, enter 4; If no, enter 0 ______Wrist: If yes, enter 4; If no, enter 0 ______|
|5. Do you currently take or have you ever taken estrogen? (ie, Premarin®, Estrace®, Estraderm®, Estratab®, Evista®)|
|If yes, enter 0If no, enter 1______|
|Add 1 thru 5, enter here ______|
|7.What is current weight in pounds? __ ____|
|Enter the number(s) in redhere. ______|
|8. Calculate Final Score|
|Subtract subtotal on line 6 from the value on line 7. Enter here. ________|
If your final score is greater than or equal to 6, you could be at risk for osteoporosis. Speak with your doctor about further evaluation.