From the Guidelines
A 39-year-old female is considered to have normal bone density if her T-score is above -1.0 and her Z-score is between -2.0 and +2.0, as indicated by the World Health Organization (WHO) criteria and the International Society for Clinical Densitometry (ISCD) recommendations 1.
Normal T-scores and Z-scores
For a woman of this age, a T-score between -1.0 and +1.0 is considered within the normal range, while a Z-score should be between -2.0 and +2.0, as T-scores compare bone density to that of a healthy young adult, and Z-scores compare to age-matched peers 1.
Bone Health Considerations
At 39, a woman typically hasn't begun to experience significant age-related bone loss, so her scores should reflect normal bone density. If T-scores fall between -1.0 and -2.5, this indicates osteopenia (low bone mass), while scores below -2.5 suggest osteoporosis, according to the WHO criteria 1.
Maintenance of Bone Health
Regular weight-bearing exercise, adequate calcium intake (1000 mg daily), and vitamin D (600-800 IU daily) help maintain bone health. If bone density testing shows abnormal results, further evaluation would be needed to determine appropriate interventions, which might include lifestyle modifications or medication depending on severity and risk factors, as suggested by the updated practice guideline for dual-energy x-ray absorptiometry (DXA) 1.
Diagnostic Classification
Diagnostic classification is based on the lowest T-score at any of the recommended DXA regions, and caution is advised when performing forearm measurements, as this is not the most relevant site for fracture risk assessment, as noted in the study 1.
From the Research
Normal T-Scores and Z-Scores
- A T-score is a comparison of a patient's bone density with healthy, young individuals of the same sex 2
- A T-score of -2.5 or less at the femoral neck defines osteoporosis 3, 4, 2
- For a 39-year-old female, a normal T-score would be above -1, as a T-score between -1 and -2.5 indicates osteopenia, which is a condition where bone density is lower than normal but not low enough to be classified as osteoporosis 3, 2
- A Z-score is a comparison with the bone density of people of the same age and sex as the patient 2
- A negative Z-score of -2.5 or less should raise suspicion of a secondary cause of osteoporosis 2
- There is no specific information available on the normal Z-score range for a 39-year-old female, as Z-scores are typically used to identify secondary causes of osteoporosis rather than to define normal bone density 2
Bone Density Measurements
- Dual energy X-ray absorptiometry (DXA) is the preferred method of calculating bone mineral density 2
- The density of the total hip is the best predictor for a hip fracture, while the lumbar spine is the best site for monitoring the effect of treatment 2
- A thoracolumbar X-ray is useful in identifying vertebral fractures 2
Osteoporosis Diagnosis and Treatment
- Osteoporosis is a condition associated with decreased bone strength and an increased fracture risk 3
- Risk factors predisposing to fractures include increasing age, female gender, low BMD, and a prior fragility fracture, among others 3, 5, 4
- Treatment is generally recommended in postmenopausal women who have a bone mineral density T score of -2.5 or less, a history of spine or hip fracture, or a Fracture Risk Assessment Tool (FRAX) score indicating increased fracture risk 4