Thyroid Testing Guidelines

Timing and Consistency

Morning testing is preferred for more accurate results, especially when assessing adrenal function simultaneously 1
The American Association of Clinical Endocrinologists recommends serial TSH measurements to establish that a thyroid disorder is real and persistent 1
For consistency in serial measurements, collecting samples at approximately the same time of day is recommended 1
For monitoring patients with known thyroid disorders, consistency in the timing of blood collection may provide more comparable results over time 1

In acute illness, thyroid function tests may be misleading (euthyroid sick syndrome) due to the effects of hyperglycemia, ketosis, weight loss, or other metabolic disturbances 2, 3
If thyroid function tests are performed during acute illness and show slight abnormalities, they should be repeated after metabolic stability is achieved 2, 3
In children with type 1 diabetes being screened for autoimmune thyroid disease, thyroid function tests should be performed when clinically stable or after glycemic control has been established 4, 3

Misinterpreting thyroid function tests during acute illness as primary thyroid dysfunction; tests should be repeated after resolution of the acute illness 1