bone density

A bone density test may detect osteoporosis or osteopenia. The usual response to either of these indications is consultation with a physician. Bone density tests are not recommended for people without risk factors for weak bones,{{Citation |author1 = American Academy of Family Physicians |author1-link = American Academy of Family Physicians |others = presented by ABIM Foundation |title = Five Things Physicians and Patients Should Question |publisher = American Academy of Family Physicians |work = Choosing Wisely: an initiative of the ABIM Foundation |url = http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_Amer_Acad_Fam_Phys.pdf |access-date = August 14, 2012 |url-status = dead |archive-url = https://web.archive.org/web/20120624075453/http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_Amer_Acad_Fam_Phys.pdf |archive-date = June 24, 2012 }}{{Citation | author1 = Consumer Reports | author-link = Consumer Reports | author2 = American Academy of Family Physicians | author2-link = American Academy of Family Physicians | date = May 2012| title = Bone-density tests: When you need them – and when you don't| publisher = Consumer Reports| work = Choosing Wisely: an initiative of the ABIM Foundation| url = http://consumerhealthchoices.org/wp-content/uploads/2012/05/ChoosingWiselyBoneDensityAAFP.pdf| access-date = August 14, 2012| archive-date = March 4, 2016| archive-url = https://web.archive.org/web/20160304075232/http://consumerhealthchoices.org/wp-content/uploads/2012/05/ChoosingWiselyBoneDensityAAFP.pdf| url-status = dead}} which is more likely to result in unnecessary treatment rather than discovery of a weakness.

The risk factors for low bone density and primary considerations for a bone density test include:

• females age 65 or older.
• males age 70 or older.
• people over age 50 with:
• previous bone fracture from minor trauma.
• rheumatoid arthritis.
• low body weight.
• a parent with a hip fracture.
• individuals with vertebral abnormalities.{{cite web|url=http://www.nof.org/osteoporosis/bonemass.htm |title=Bone Mass Measurement |access-date=2008-03-20 |work=NOF |archive-url=https://web.archive.org/web/20080307014020/http://www.nof.org/osteoporosis/bonemass.htm |archive-date=2008-03-07 |url-status=dead }}
• 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.
• when androgen deprivation therapy is being planned for prostate cancer.
• individuals with a history of eating disorders.

Other considerations that are related to risk of low bone density and the need for a test include smoking habits, drinking habits, the long-term use of corticosteroid drugs, and a vitamin D deficiency.

Results of the test are reported in three forms:

• Measured areal density in g cm⁻².
• Z-score: the number of standard deviations above or below the mean for the patient's age, sex and ethnicity.
• T-score: the number of standard deviations above or below the mean for a healthy 30-year-old adult of the same sex and ethnicity as the patient.

File:Blausen 0095 BoneDensitometryScan.png

While there are many types of bone mineral density tests, all are non-invasive. The tests differ according to which bones are measured to determine the test result.

These tests include:

• Dual-energy X-ray absorptiometry (DXA or DEXA)
• Trabecular bone score
• Dual X-ray Absorptiometry and Laser (DXL)
• Quantitative computed tomography (QCT)
• Quantitative ultrasound (QUS)
• Single photon absorptiometry (SPA)
• Dual photon absorptiometry (DPA)
• Digital X-ray radiogrammetry (DXR)
• Single energy X-ray absorptiometry (SEXA)

DXA is the most commonly used testing method {{asof|2016|lc=y}}. The DXA 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 the risk for fractures and the stage of osteoporosis (if any) in an individual.

Quantitative ultrasound (QUS) has been described as a more cost-effective approach for measuring bone density, as compared to DXA.{{cite web |title=Bone densitometry |url=http://courses.washington.edu/bonephys/opbmd.html |access-date=2008-09-02}}

Average bone mineral density = BMC / W [g/cm²]

• BMC = bone mineral content = g/cm
• W = width at the scanned line

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.

Less than 0.5% of patients who underwent DXA-scanning were found to have a T- or Z-score of more than +4.0, often the cause of an unusually high bone mass (HBM) and associated with mild skeletal dysplasia and the inability to float in water.{{cite journal |vauthors=Gregson CL, Steel SA, O'Rourke KP, Allan K, Ayuk J, Bhalla A, Clunie G, Crabtree N, Fogelman I, Goodby A, Langman CM, Linton S, Marriott E, McCloskey E, Moss KE, Palferman T, Panthakalam S, Poole KE, Stone MD, Turton J, Wallis D, Warburton S, Wass J, Duncan EL, Brown MA, Davey-Smith G, Tobias JH |title='Sink or swim': an evaluation of the clinical characteristics of individuals with high bone mass |journal=Osteoporos Int |volume=23 |issue=2 |pages=643–54 |date=February 2012 |pmid=21455762 |pmc=3261396 |doi=10.1007/s00198-011-1603-4 }}

The T-score is the relevant measure when screening for osteoporosis. It is the bone mineral density at the site when compared to the "young normal reference mean". It is a comparison of a patient's bone mineral density to that of a healthy 30-year-old.{{Cite web|title=Bone Density Scan: MedlinePlus Medical Test|url=https://medlineplus.gov/lab-tests/bone-density-scan/|access-date=2020-10-29|website=medlineplus.gov|language=en}} The US standard is to use data for a 30-year-old of the same sex and ethnicity, but the WHO recommends using data for a 30-year-old white female for everyone.{{cite web|url=http://courses.washington.edu/bonephys/opbmdtz.html |title=T and Z scores. |access-date=2013-06-22 |date=2011-07-29 |publisher=University of Washington Bone Physics }} Values for 30-year-olds are used in post-menopausal women and men over age 50 because they better predict risk of future fracture.{{cite web |url=http://www.guideline.gov/summary/summary.aspx?ss=15&doc_id=11559&nbr=5990 |title=Osteoporosis and bone mineral density. |access-date=2008-05-11 |last=Richmond |first=Bradford |date=2007-11-13 |publisher=American College of Radiology |archive-url=https://web.archive.org/web/20080917114051/http://guideline.gov/summary/summary.aspx?ss=15&doc_id=11559&nbr=5990 |archive-date=2008-09-17 |url-status=dead }} The criteria of the World Health Organization are:{{cite web | author=((WHO Scientific Group on the Prevention and Management of Osteoporosis)) |url=http://whqlibdoc.who.int/trs/WHO_TRS_921.pdf |title=Prevention and management of osteoporosis : report of a WHO scientific group| year=2003 |access-date=2007-05-31 }}

• Normal is a T-score of −1.0 or higher{{Cite web|title=Bone Mass Measurement: What the Numbers Mean |work=NIH Osteoporosis and Related Bone Diseases National Resource Center|url=https://www.bones.nih.gov/health-info/bone/bone-health/bone-mass-measure#b|access-date=2021-03-12 |publisher=National Institute for Health}}
• Osteopenia is defined as between −1.0 and −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 30-year-old man/woman.

The Z-score for bone density is the comparison to the "age-matched normal" and is usually used in cases of severe osteoporosis. This is the standard score or number of standard deviations a patient's bone mineral density differs from the average for their age, sex, and ethnicity. This value is used in premenopausal women, men under the age of 50, and in children and adolescents.{{cite journal | vauthors = Bachrach LK | title = Assessing bone health in children: who to test and what does it mean? | journal = Pediatr Endocrinol Rev | volume = 2 | issue = Suppl 3| pages = 332–6 | date = February 2005 | pmid = 16456501 | doi = | url = }} It is most useful when the score is less than 2 standard deviations below this normal. In this setting, it is helpful to scrutinize for coexisting illnesses or treatments that may contribute to osteoporosis such as glucocorticoid therapy, hyperparathyroidism, or alcoholism.

To prevent low bone density it is recommended to have sufficient calcium and vitamin D.{{Cite web|url=https://www.webmd.com/osteoporosis/features/building-stronger-bones|title=Building Stronger Bones|last=Lawrence|first=Jean|website=WebMD|language=en|access-date=2020-04-20}}{{Cite web|url=https://www.mayoclinic.org/healthy-lifestyle/adult-health/in-depth/bone-health/art-20045060|title=How to keep your bones healthy|website=Mayo Clinic|language=en|access-date=2020-04-20}} Sufficient calcium is defined as 1,000 mg per day, increasing to 1,200 mg for women above 50 and men above 70. Sufficient vitamin D is defined as 600 IUs per day for adults 19 to 70, increasing to 800 IUs per day for those over 71. Exercise, especially weight-bearing and resistance exercises are most effective for building bone. Weight-bearing exercise includes walking, jogging, dancing, and hiking. Resistance exercise is often accomplished through lifting weights.{{Cite web|title=Exercise for Your Bone Health |work=NIH Osteoporosis and Related Bone Diseases National Resource Center|url=https://www.bones.nih.gov/health-info/bone/bone-health/exercise/exercise-your-bone-health|access-date=2020-11-09 |publisher=National Institute for Health }} Other therapies, such as estrogens (e.g., estradiol, conjugated estrogens), selective estrogen receptor modulators (e.g., raloxifene, bazedoxifene), and bisphosphonates (e.g., alendronic acid, risedronic acid), can also be used to improve or maintain bone density. Tobacco use and excessive alcohol consumption have detrimental effects on bone density.{{Cite web |title=Smoking and Bone Health |work=NIH Osteoporosis and Related Bone Diseases National Resource Center |url=https://www.bones.nih.gov/health-info/bone/osteoporosis/conditions-behaviors/bone-smoking |access-date=2022-09-19 |publisher=National Institute for Health }} Excessive alcohol consumption is defined as more than one standard-sized alcoholic beverage per day for women, and drinking two or more alcoholic beverages per day for men.

Bone mineral density is highly variable between individuals. While there are many environmental factors that affect bone mineral density, genetic factors play the largest role.{{Cite journal |last1=Goolsby |first1=Marci A. |last2=Boniquit |first2=Nicole |date=2016 |title=Bone Health in Athletes |journal=Sports Health |volume=9 |issue=2 |pages=108–117 |doi=10.1177/1941738116677732 |pmc=5349390 |pmid=27821574}}{{Cite journal |last1=Yang |first1=Tie-Lin |last2=Shen |first2=Hui |last3=Liu |first3=Anqi |last4=Dong |first4=Shan-Shan |last5=Zhang |first5=Lei |last6=Deng |first6=Fei-Yan |last7=Zhao |first7=Qi |last8=Deng |first8=Hong-Wen |date=February 2020 |title=A road map for understanding molecular and genetic determinants of osteoporosis |journal=Nature Reviews Endocrinology |language=en |volume=16 |issue=2 |pages=91–103 |doi=10.1038/s41574-019-0282-7 |pmc=6980376 |pmid=31792439}} Bone mineral density variation has been estimated to have 0.6–0.8 heritability factor, meaning that 60–80% of its variation is inherited from parents.{{Cite journal |last1=Peacock |first1=Munro |last2=Turner |first2=Charles H. |last3=Econs |first3=Michael J. |last4=Foroud |first4=Tatiana |date=2002-06-01 |title=Genetics of Osteoporosis |journal=Endocrine Reviews |volume=23 |issue=3 |pages=303–326 |doi=10.1210/edrv.23.3.0464 |pmid=12050122|doi-access=free }} Because of the heritability of bone mineral density, family history of fractures is considered as a risk factor for osteoporosis. Bone mineral density is polygenic and many of the genetic mechanisms remain poorly understood.

There are several rare genetic diseases that have been associated with pathologic changes in bone mineral density. The table summarizes these diseases:{{Cite journal |last1=Marom |first1=Ronit |last2=Rabenhorst |first2=Brien M. |last3=Morello |first3=Roy |date=2020-10-01 |title=Management of Endocrine Disease: Osteogenesis imperfecta: an update on clinical features and therapies |url=https://eje.bioscientifica.com/view/journals/eje/183/4/EJE-20-0299.xml |journal=European Journal of Endocrinology |volume=183 |issue=4 |pages=R95–R106 |doi=10.1530/EJE-20-0299 |pmc=7694877 |pmid=32621590}}{{Cite journal |last1=Huang |first1=Qing-Yang |last2=Kung |first2=Annie Wai Chee |date=2006-08-01 |title=Genetics of osteoporosis |url=https://www.sciencedirect.com/science/article/pii/S1096719206001648 |journal=Molecular Genetics and Metabolism |volume=88 |issue=4 |pages=295–306 |doi=10.1016/j.ymgme.2006.04.009 |pmid=16762578 |url-access=subscription }}

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Category:Mass density

Category:Bones