Prevention, Screening and Health Maintenance
Family Medicine Clerkship
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Upon completion of this unit, you will be familiar with:
- Imaging procedures considered for early detection of
- Mechanism and limitation of bone densitometry scan
- Radiological criteria for osteoporosis
- Sensitivity and specificity of bone densitometry
- Identification of high risk individuals
- Annual screen
- Cost for population screening
- cost per procedure
- number of potential subjects
- Morbidity advantage of early detection
What is osteoporosis?
- Decrease in bone matrix
- Mineralization is preserved
What are the risk factors for osteoporosis?
Risk factors for osteoporosis include:
- Long term use of steroids
How do patients with osteoporosis present or when would
you suspect osteoporosis?
- Loss of height with aging
- Kyphosis with aging
- Compression fractures of vertebra
- Be suspicious of osteoporosis in a patient exhibiting
the following signs:
- Any fracture after age 40
- Adult weighing less than 125lbs
- Fracture of wrist, spine or hip in first-degree
relative after age 50
What are the commonly used types of peripheral bone
density measurements and how do they compare? Which is the
Dual-energy X-ray Absorptiometry (DXA):
- Posteroanterior lumbar spine and proximal femur
- X-rays with two energy peaks are produced, allowing
diff. absorption of radiation by bone and soft tissue,
from which BMD is calculated
- GOLD STANDARD
Quantitative CT (QCT):
- Lumbar spine
- Unique in that it measures trabecular bone density
- Probably the most sensitive test in measuring changes
in bone density, however it is not as precise as DXA and
it is not as widely used because of higher radiation dose.
What bone density measurement site correlates best with
clinically important fractures?
- The hip is the best site for predicting clinically
- Relative risk of fracture per 1 SD change
A postmenopausal 53-year-old white woman comes to clinic
for an annual physical. Her exam is normal. She has come
across many advertisements regarding osteoporosis screening.
What would you recommend?
A: Order bone mineral density scan
B: Empiric preventive treatment for osteoporosis
C: Need more clinical information prior to giving
For women over the age of 50 and under 65, you need at
least one risk factor to recommend bone mineral density
A 66 y/o white female comes to the clinic for routine
follow up. She is concerned about osteoporosis and being
that she is over 65, she qualifies for a bone mineral
density scan. A DXA shows total hip bone mineral density
0.93 SD above the 66-year-old mean and 0.36 SD below the
25-year-old mean. T score is reported as -036 and her Z
score is 0.93.
What is a T-score?
T-SCORE = the number of standard deviations the bone
mineral density measurement is above or below the
YOUNG-NORMAL MEAN bone mineral density.
What is a Z-score?
Z-SCORE = the number of standard deviations the
measurement is above or below the AGE -MATCHED MEAN bone
How do you use T and Z scores in clinical decision?
A bone mineral density more than 2.5 standard deviations
below the mean for a young healthy adult white woman
identifies 30 percent of all postmenopausal women as having
osteoporosis; half of these women will already have had a
The hip T-score is the site used in clinical decisions.
Z-score is less commonly used but may be helpful in
identifying persons who should undergo a work-up for
secondary causes of osteoporosis.
A Z-score changes over time in relation to the T-score.
Converting T-score to Z-score at the hip:
- Age 50: T = Z - 0.37
- Age 60: T = Z - 1.01
- Age 70: T = Z - 1.56
- Age 80: T = Z - 2.11
- Age 90: T = Z - 2.52
What factors contribute to the estimate of the annual
cost of screening all potential subjects in United States?
Cost of the program depends on:
- Number of women over 65
- Number of women between 50-65 with risk factor
- Cost of DXA
How do you justify the cost of annual screening for
- Prevention of morbidity due to vertebral fractures.