Thyroid Function Assessment Guidelines

Reference Ranges and Interpretation

• The American Association of Clinical Endocrinologists recommends using the laboratory's established reference range for free T4, typically without age adjustment 1
• Each laboratory should establish its own reference intervals using the specific immunoassay platform employed, as reference intervals vary significantly between different manufacturer assays 2
• FT4 should always be interpreted in conjunction with TSH levels for comprehensive thyroid function assessment 3
• Normal FT4 with abnormal TSH indicates subclinical thyroid dysfunction 1, 3

Medications and External Factors Affecting Thyroid Function

• Amiodarone can alter thyroid hormone levels 3
• Dopamine, glucocorticoids, and dobutamine can affect TSH without causing true hyperthyroidism 1
• Non-thyroidal illness can cause abnormal thyroid function tests without actual thyroid dysfunction 1
• Iodine exposure from CT contrast can transiently impact thyroid function tests 1