Bone mineral density
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2008-06-11T23:29:55Z
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'''Bone mineral density''' ('''BMD''' or '''Bone mass''' ) is a measure of the amount of [[Bone#Molecular_structure|minerals]] (mainly calcium) contained in a certain volume of [[bone]]. [[Calcium]] gives bones their strength and helps prevent [[bone fracture|fractures]]. A bone mineral density (BMD) test, also called a ''bone mass measurement'', is used to measure bone density and determine fracture risk for [[osteoporosis]]. It may also be used to determine how effective an osteoporosis treatment is.
==Candidates==
The [[National Osteoporosis Foundation]] recommends BMD testing for the following individuals:<ref name="titleNOF - Bone Mass Measurement">{{cite web |url=http://www.nof.org/osteoporosis/bonemass.htm |title=NOF - Bone Mass Measurement |accessdate=2008-03-20 |format= |work=}}</ref>
*All women aged 65 and older regardless of risk factors
*Younger [[menopause|postmenopausal]] women with one or more risk factors.
*Postmenopausal women who present with fractures (to confirm the diagnosis and determine disease severity).
*[[Estrogen]] deficient women at clinical risk for osteoporosis.
*Individuals with [[vertebrae|vertebral]] abnormalities.
*Individuals receiving, or planning to receive, long-term glucocorticoid ([[steroid]]) therapy.
*Individuals with primary [[hyperparathyroidism]].
*Individuals being monitored to assess the response or efficacy of an approved osteoporosis drug therapy.
==Types of tests==
While there are many different types of BMD tests, all are non-invasive. Most tests differ in which bones are measured to determine the BMD result.
These tests include:
*[[DEXA|Dual Energy X-ray Absorptiometry]] (DXA or DEXA)
*[[QCT|Quantitative Computed Tomography]] (QCT)
*[[QUS|Qualitative Ultrasound]] (QUS)
*[[Single Photon Absorptiometry]] (SPA)
*[[Dual Photon Absorptiometry]] (DPA)
*[[DXR|Digital X-ray Radiogrammetry]] (DXR)
*[[SEXA|Single Energy X-ray Absorptiometry]] (SEXA)
The test works by measuring a specific [[bone]] or bones, usually the spine, hip, and wrist. The density of these bones is then compared with an average index based on age, sex, and size. The resulting comparison is used to determine risk for fractures and the stage of osteoporosis in an individual.
Average bone mineral density = BMC / W [g/cm²]
*BMC = bone mineral content = g/cm
*W = width at the scanned line
==Interpretation==
Results are generally scored by two measures, the [[T-score]] and the [[Z-score]]. Scores indicate the amount one's bone mineral density varies from the mean. Negative scores indicate lower bone density, and positive scores indicate higher.
===T-score===
The T-score is a comparison of a patient's BMD to that of a healthy thirty-year-old of the same sex and ethnicity. This value is used in post-menopausal women and men over aged 50 because it better predicts risk of future fracture.<ref name="Richmond"> {{cite web|url=http://www.guideline.gov/summary/summary.aspx?ss=15&doc_id=11559&nbr=5990 |title=Osteoporosis and bone mineral density. |accessdate=2008-05-11 |last=Richmond |first=Bradford |date=2007-11-13 |publisher=American College of Radiology }}</ref>The criteria of the [[World Health Organization]] are<ref name="WHOcriteria">{{cite web | author=WHO Scientific Group on the Prevention and Management of Osteoporosis (2000 : Geneva, Switzerland) |url=http://whqlibdoc.who.int/trs/WHO_TRS_921.pdf |title=Prevention and management of osteoporosis : report of a WHO scientific group| year=2003 |accessdate=2007-05-31 |format=pdf |work=}}</ref>:
* Normal is a T-score of -1.0 or higher
* [[Osteopenia]] is defined as less than -1.0 and greater than -2.5
* [[Osteoporosis]] is defined as -2.5 or lower, meaning a bone density that is two and a half standard deviations below the mean of a thirty year old woman.
{| class="wikitable" align="center"
|+ Hip fractures per 1000 patient-years<ref name="pmid17846439">{{cite journal |author=Cranney A, Jamal SA, Tsang JF, Josse RG, Leslie WD |title=Low bone mineral density and fracture burden in postmenopausal women |journal=CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne |volume=177 |issue=6 |pages=575–80 |year=2007 |pmid=17846439 |doi=10.1503/cmaj.070234}}</ref>
! WHO category !! Age 50-64 !! Age > 64 || Overall
|-
| Normal || 5.3 || 9.4 || 6.6
|-
| [[Osteopenia]] || 11.4 || 19.6 || 15.7
|-
| [[Osteoporosis]] || 22.4 || 46.6 || 40.6
|}
===Z-score===
The Z-score is the number of standard deviations a patient's BMD differ from the average BMD of their age, sex, and ethnicity. This value is used in premenopausal women, men under the age of 50, and in children.<ref name="Richmond"> </ref>
==See also==
*[[Osteoporosis]]
*[[Osteopenia]]
*[[Bone]]
==References==
{{reflist}}
== External links ==
* [http://www.cancer.gov/Templates/db_alpha.aspx?CdrID=415884 Bone mass] entry in the public domain NCI Dictionary of Cancer Terms
{{NCI-cancer-dict}}
[[Category:Medical tests]]
[[Category:Skeletal system]]
[[es:Densitometría osea]]
[[it:Densità minerale ossea]]
[[pl:BMD (medycyna)]]