DEXA

A DEXA (Dual-Energy X-ray Absorptiometry) scan is a medical imaging technique used to measure bone mineral density (BMD). It’s commonly used to diagnose osteoporosis and assess an individual’s risk of bone fractures. Two important values provided by a DEXA scan report are the T-score and the Z-score. The units of both T and Z scores are standard deviations from the mean.

Here’s what they represent:

• T-score:
  • This score compares your BMD to the average peak bone mass of a healthy young adult of the same sex.
  • Interpretation:
    • Normal: T-score is above -1.0.
    • Osteopenia (or low bone mass): T-score is between -1.0 and -2.5. It indicates a below-average bone density but not low enough to be classified as osteoporosis.
    • Osteoporosis: T-score is -2.5 or lower.
    • The T-score is the primary value used to diagnose osteoporosis, especially in postmenopausal women and men aged 50 and older.
• Z-score:
  • This score compares your BMD to the average bone mass of people your own age, sex, weight, and ethnic or racial origin.
  • Interpretation:
    • If the Z-score is -2.0 or lower, it suggests that something other than aging is causing abnormal bone loss.
    • While the Z-score can provide additional information, the diagnosis of osteoporosis or osteopenia is based on the T-score.

It’s essential to understand that while the T-score and Z-score provide valuable information about bone health, the decision to start treatment for osteoporosis doesn’t solely depend on DEXA scan results. Other factors, like an individual’s risk factors, history of fractures, and overall health, play a role in the clinical decision-making process.

Indications

Here are some general indications for a DEXA scan:

• Age 70 and older, irrespective of risk factors (single screening scan)
• Age 50-69 with risk factors for fracture.
• Adults who have had a fragility fracture: To determine the extent of bone loss and the risk of future fractures.
• Patients with radiographic findings that suggest osteoporosis: Vertebral fractures or osteopenia.
• Individuals with diseases or conditions associated with bone loss:
  • rheumatoid arthritis,
  • chronic kidney disease,
  • chronic liver disease
  • eating disorders, etc.
  • long-term glucocorticoid therapy ie 7.5 mg/day or more for over 3 months.
  • primary hyperparathyroidism
  • hypogonadism
  • HIV
• Patients undergoing certain drug therapies known to cause bone loss:
  • aromatase inhibitors for breast cancer,
  • androgen deprivation therapy for prostate cancer
  • some antiseizure medications (carbamazepine, phenobarbitone, phenytoin, valproate)
  • tenofovir (HIV and HBV)
• Pre-transplant evaluation
• To monitor treatment efficacy

This list is not exhaustive and the decision to perform a DEXA scan is typically based on a combination of clinical judgment, individual risk factors, and established guidelines.