Diagnostic Criteria for Osteoporosis Based on Bone Density

Classification According to T-Score by DXA

The World Health Organization (WHO) diagnoses osteoporosis with a T-score ≤ -2.5 at the lumbar spine, femoral neck, or total hip measured by dual-energy X-ray absorptiometry (DXA) 1, 2, 3
Normal bone density is defined as a T-score ≥ -1.0, according to the WHO criteria 1, 2, 3
Osteopenia (low bone mass) is defined as a T-score between -1.0 and -2.5, as established by the WHO 1, 2, 3
Osteoporosis is defined as a T-score ≤ -2.5, as per the WHO criteria 1, 2, 3

A fragility fracture replaces any DXA measurement to establish an osteoporosis diagnosis, as stated by the American College of Radiology 2, 3
Patients in the osteopenic range who experience a fragility fracture should be reclassified with an osteoporosis diagnosis, regardless of their T-score, according to the American College of Radiology 2, 3

The lumbar spine is a primary site for DXA evaluation, measuring up to 4 vertebral bodies from L1 to L4, as recommended by the American College of Radiology 3
The hip is another primary site, measuring the femoral neck and total hip, as per the American College of Radiology 3

The WHO criteria based on T-score do not apply to volumetric QCT of the vertebral spine, as stated by the American College of Radiology 2, 3, 4
The American College of Radiology (ACR) thresholds for QCT are: low bone mass/osteopenia: 80-120 mg/mL, and osteoporosis: <80 mg/mL 2, 4

The Z-score represents the number of standard deviations above or below the mean of age-matched controls and is used to detect secondary causes of osteoporosis, rather than primary diagnosis, as recommended by the American College of Radiology 1, 3

Underutilization of DXA remains a problem, with only 6.7% of patients undergoing DXA evaluation within 6 months of a fragility fracture, and only 8% of patients on long-term corticosteroid therapy having follow-up DXA, according to the American College of Radiology 2, 3