Bone Density Testing in Hypothyroidism
Bone density testing is not routinely indicated for hypothyroidism alone, but should be ordered for patients with hypothyroidism who have additional osteoporosis risk factors such as postmenopausal status, age >65 years, prior fractures, glucocorticoid use, or malabsorption. 1
When to Order Bone Density Testing
Patients with hypothyroidism who meet standard screening criteria:
- Women age ≥65 years should undergo bone density testing regardless of hypothyroidism status 1
- Postmenopausal women with hypothyroidism and at least one additional risk factor (prior fracture, family history, smoking, low body weight) 1
- Men age >50 years with hypothyroidism plus additional risk factors 1
- Any patient with hypothyroidism receiving chronic glucocorticoid therapy (>3 months) 1
- Patients with hypothyroidism and history of low-trauma fractures 1
- Patients with hypothyroidism and documented malabsorption 1
Hypothyroidism-specific considerations:
- Hypothyroidism itself is not listed as an independent indication for bone density testing in major guidelines 1
- The primary concern for bone loss relates to subclinical hyperthyroidism or overtreatment with levothyroxine, not undertreated hypothyroidism 1, 2
- Postmenopausal women on levothyroxine with suppressed TSH (<0.1 mIU/L) have increased fracture risk and warrant bone density assessment 1
Important Clinical Pitfalls
Overtreatment concerns:
- Excessive levothyroxine dosing that suppresses TSH can cause bone loss, particularly in postmenopausal women 1, 2
- Meta-analyses show that exogenous subclinical hyperthyroidism (from overtreatment) results in significant BMD loss in postmenopausal women but not premenopausal women 1
- Monitor TSH levels 6-8 weeks after initiating or adjusting levothyroxine, then annually to avoid overtreatment 3
Bone density changes during treatment initiation:
- When starting levothyroxine for overt hypothyroidism, some studies show transient 5-13% bone density reductions in the first year 4, 2
- However, treating subclinical hypothyroidism does not cause short-term bone density reduction 5
- Long-term appropriately dosed levothyroxine therapy does not increase fracture risk when TSH is maintained in normal range 6, 2
Testing Methodology
- DXA of lumbar spine and hip(s) is the preferred modality for patients meeting screening criteria 1
- Distal forearm DXA should be used when hip/spine cannot be measured or in patients with hyperparathyroidism 1
- Repeat testing intervals: every 2 years for osteopenia with T-score ≤-2.0, or 1-2 years after therapy initiation 1, 7
- Scan intervals <1 year are discouraged 1, 7
Key Takeaway
The decision to order bone density testing should be based on standard osteoporosis risk factors, not on the presence of hypothyroidism alone. The critical issue is ensuring adequate—but not excessive—levothyroxine replacement to maintain TSH in the normal range, thereby avoiding the bone loss associated with iatrogenic subclinical hyperthyroidism. 1, 3, 2