ISCD CCD flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

T-score definition

The number of standard deviations a patient's BMD lies above or below the mean BMD of a young, sex-matched reference population; used for WHO osteoporosis diagnosis in postmenopausal women and men 50 and older.

Z-score definition

The number of standard deviations a patient's BMD lies from the mean of an age-, sex-, and ethnicity-matched reference population; used to identify low bone mass for age in younger individuals.

Osteoporosis T-score threshold

A T-score of −2.5 or lower at the lumbar spine, total hip, femoral neck, or 33% radius meets the WHO densitometric definition of osteoporosis in eligible adults.

Osteopenia T-score range

A T-score between −1.0 and −2.5 defines low bone mass (osteopenia); it is a risk category, not a disease diagnosis, and treatment depends on fracture risk.

Least significant change

The smallest BMD difference between two measurements that is statistically significant at 95% confidence; calculated as 1.96 times the square root of 2 times the precision error.

Areal versus volumetric BMD

DXA reports areal BMD in g/cm², which depends on bone size; QCT reports true volumetric BMD in mg/cm³ and is less affected by body size and degenerative artifact.

Vertebrae to exclude

Vertebrae that are fractured, instrumented, or affected by focal structural change or artifact should be excluded; at least two evaluable vertebrae are needed for a valid spine result.

Valid diagnostic sites

The WHO classification applies to lumbar spine, total hip, femoral neck, and 33% radius; the lowest valid T-score among these sites determines the diagnosis.

DXA radiation dose

A DXA scan delivers an effective dose of roughly 1 to 10 microsieverts, similar to a few hours of natural background radiation and far below a chest radiograph.

Precision assessment requirement

Each DXA facility should perform an in vivo precision study on volunteers to establish site-specific precision error and LSC before interpreting serial BMD changes.

Phantom scanning purpose

A spine phantom is scanned regularly to monitor scanner stability and drift; a shift in phantom BMD signals a need for service or recalibration before clinical results are trusted.

Bone mineral content

BMC is the total mineral mass in grams within the region of interest; BMD equals BMC divided by the projected bone area in cm².

Artifact effect on BMD

Metal hardware, calcified vessels, contrast, and degenerative changes can falsely raise spine BMD; recognizing artifact prevents misclassification and inappropriate reassurance.

Who needs BMD testing

Testing is indicated for women 65 and older, men 70 and older, younger adults with risk factors, and anyone with a fragility fracture or disease causing bone loss.

FRAX tool inputs

FRAX calculates 10-year major osteoporotic and hip fracture probability from age, sex, BMI, prior fracture, parental hip fracture, smoking, glucocorticoids, rheumatoid arthritis, secondary osteoporosis, alcohol, and optionally BMD.

FRAX treatment thresholds

In the United States, pharmacologic therapy is generally recommended when 10-year major osteoporotic probability is 20% or higher or hip fracture probability is 3% or higher.

FRAX limitations

FRAX is not validated for patients already on osteoporosis treatment and does not account for dose or duration of glucocorticoids or for number of prior fractures.

Fragility fracture definition

A fracture occurring from a fall from standing height or less, or from trauma that would not break normal bone, is a fragility fracture and warrants bone density evaluation.

Vertebral fracture assessment

VFA uses the DXA image to detect vertebral deformities; a moderate or severe vertebral fracture predicts future fracture independent of BMD.

Secondary osteoporosis causes

Common causes include glucocorticoid use, hyperparathyroidism, hyperthyroidism, vitamin D deficiency, hypogonadism, malabsorption, multiple myeloma, and chronic kidney disease.

Glucocorticoid bone loss

Bone loss is most rapid in the first 3 to 6 months of glucocorticoid therapy; fracture risk rises quickly and BMD monitoring is recommended early.

Repeat DXA interval

Repeat DXA is generally not indicated before two years unless rapid change is expected, such as with glucocorticoids or recent initiation of therapy.

Bone turnover markers

Markers such as serum CTX (resorption) and P1NP (formation) reflect bone remodeling; they help assess adherence and treatment response but cannot diagnose osteoporosis.

Monitoring treatment response

A BMD increase is considered a real response only when it exceeds the least significant change at that site; otherwise it may reflect measurement variability.

Lumbar spine BMD pitfalls

Spine BMD may be falsely elevated by degenerative disease, aortic calcification, or scoliosis; hip BMD or radius may be preferable when spine results are unreliable.

Hip region of interest

Total hip and femoral neck are the standard hip sites; the femoral neck is preferred for diagnosis, and the total hip is often used for monitoring.

Bilateral hip scanning

Scanning both hips is useful when one hip is affected by prior fracture or arthroplasty; the lower of the valid hip measurements is used for classification.

Body composition on DXA

DXA can quantify total and regional lean and fat mass, but body composition is not the primary purpose of a clinical bone density study.

Trabecular bone score

TBS is a texture index derived from lumbar spine DXA images that reflects trabecular microarchitecture and adds fracture risk information beyond BMD.

Calcium and vitamin D

Adequate calcium intake and vitamin D sufficiency support bone health and are prerequisites for osteoporosis pharmacotherapy; severe deficiency should be corrected first.

Fall risk assessment

Falls are a major fracture determinant; assessing gait, balance, vision, medications, and home hazards is part of skeletal health evaluation alongside BMD.

Reporting DXA results

A DXA report should include BMD, T-scores, Z-scores, sites measured, comparison to prior studies with LSC context, and a diagnostic classification with fracture risk comment.