SHBG Levels in Hyperthyroidism
In hyperthyroidism, SHBG levels can increase significantly, reaching values as high as 146 ± 111 nmol/L compared to normal levels of approximately 36.3 nmol/L in euthyroid individuals. 1, 2
Relationship Between Thyroid Hormones and SHBG
Thyroid hormones have a direct and significant impact on sex hormone-binding globulin (SHBG) production:
- SHBG levels are markedly elevated in hyperthyroidism and decreased in hypothyroidism 3
- There is a positive correlation between free thyroid hormone concentrations and SHBG levels 3
- In patients with overt hyperthyroidism, SHBG levels can be approximately 3-4 times higher than normal control values 2, 4
Diagnostic Value of SHBG in Thyroid Disorders
SHBG serves as a valuable metabolic marker of thyroid hormone action at the liver level:
- SHBG offers a clear and reliable parameter of thyroid hormone effects on liver cells 2
- In hyperthyroid patients, SHBG levels have been reported as high as 4.85 ± 2.4 μg DHT/100 ml compared to 1.50 ± 0.57 in normal controls 4
- There is a stronger correlation between SHBG and T3 (r=0.76) than with T4 (r=0.65), reflecting that T3 is a better indicator of metabolic thyroid effects 4
Clinical Implications of Elevated SHBG in Hyperthyroidism
The elevation of SHBG in hyperthyroidism has several clinical implications:
- Increased SHBG leads to altered sex hormone binding and bioavailability 1
- Despite elevated total testosterone in male hyperthyroid patients, free testosterone levels may be decreased due to increased SHBG binding 1
- SHBG levels normalize with successful treatment of hyperthyroidism 3, 1, 4
Monitoring SHBG During Treatment
SHBG can be used to monitor treatment response in hyperthyroidism:
- After successful antithyroid treatment, SHBG levels gradually decrease to normal ranges 1, 4
- Persistently elevated SHBG may indicate ongoing hyperthyroidism even in patients who appear clinically euthyroid 4
- SHBG normalization correlates with restoration of normal thyroid function 3
Diagnostic Pitfalls and Considerations
When interpreting SHBG levels in the context of thyroid disorders:
- SHBG levels are generally higher in women than in men with similar thyroid status 3
- A TSH of 0.01 mIU/L strongly suggests hyperthyroidism (sensitivity 98%, specificity 98%) 5
- When evaluating hyperthyroidism with very low TSH values (<0.1 mIU/L), third-generation TSH assays with functional sensitivity ≤0.01 mIU/L provide better discrimination between different degrees of TSH suppression 6
- SHBG can be particularly valuable in evaluating patients with discrepancies between clinical presentation and biochemical thyroid function tests 4