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Bone Mineral Density
Aka: Bone Mineral Density, Bone Densitometry, T-Score, Z-Score
- See Also
- Osteoporosis
- Indications: Osteoporosis Evaluation
- Patient is indecisive on starting Estrogen Replacement
- Direct management of asymptomatic Hyperparathyroidism
- Incidental radiographic evidence of bone loss
- Signs of Osteoporosis in female patients
- Height loss
- Osteoporotic Fracture
- Patients at high risk for Osteoporosis
- See Osteoporosis Evaluation for risk factors
- Longterm Corticosteroids (Prednisone 7.5 mg/day)
- AACE: Corticosteroid use for over 1 month
- Medicare: Corticosteroid use for over 3 months
- Monitor benefits of current Osteoporosis Management
- Bisphosphonates
- Estrogen Replacement Therapy
- Imaging Modalities
- Dual Energy XRAY Absorptiometry (DEXA)
- Quantitative Computed Tomography (QCT)
- Calcaneal Ultrasonography
- Score Types
- General
- Scores are not interchangeable across imaging types
- Scores are based on standard deviations below mean
- Example: T-Score of -2 is two S.D. below the mean
- T-Score (WHO standard BMD measure)
- Mean based on average premenopausal woman
- Fracture risk increases 2-3x per T unit
- T-Score is best indicator of Fracture risk
- Example: T-Score of -2 confers Fracture risk 4-6x
- Z-Score
- Mean based on women of similar Osteoporosis risk
- Accounts for age, weight, and ethnicity
- Fracture risk increases 2x per Z unit
- Measures Fracture risk for remaining lifespan
- Example: Z-Score of -2 confers Fracture risk 4x
- Interpretation: T-Score or Z-Score
- Normal: <1 Standard Deviation (SD) below the mean
- Osteopenia: 1.0 to 2.5 SD below the mean
- Osteoporosis: >2.5 SD below the mean
- Prognosis
- Risk of Fracture also related to scoring above
- Bone Mineral Density more than 2 SD below mean
- Risk of Fracture increases exponentially
- Each 10% decrease in spinal Bone Mineral Density
- Associated with 2 times risk of Vertebral Fracture
- Each 15% decrease in hip Bone Mineral Density
- Associated with 2.5 times risk of Hip Fracture
- References
- Sturtridge (1996) Can Med Assoc J 155:924 [PubMed]
- References
- Blake (1998) Endocrinol Metab Clin North Am 27:267-88 [PubMed]
- Bracker (1998) Postgrad Med 104(4):77-86 [PubMed]
- Brunader (2002) Am Fam Physician 65(7):1357-64 [PubMed]
- Genant (1998) Radiographics 18:913-8 [PubMed]