Thyroid Dysfunction Evaluation and Management

Clinical Indications for Thyroid Testing

Unexplained fatigue, weight gain, hair loss, cold intolerance, constipation, and depression are classic hypothyroid symptoms that warrant initial TSH testing 1
Weight loss, palpitations, heat intolerance, tremors, anxiety, and diarrhea indicate possible thyrotoxicosis, requiring TSH, free T4, and total T3 measurement 1
Asymptomatic patients on routine monitoring may show high free T4 or T3 with low/normal TSH, particularly common with painless thyroiditis 1
Symptoms may be masked in patients taking beta-blockers, making biochemical testing even more critical 1

Confirmed biochemical hypothyroidism (high TSH, low free T4) warrants anti-TPO antibody testing to identify autoimmune etiology 1, 2
Positive anti-TPO antibodies predict higher progression risk to overt hypothyroidism (4.3% per year vs 2.6% in antibody-negative individuals) 2

Thyroid dysfunction occurs in 6-20% of patients on immune checkpoint inhibitors, with higher rates (up to 20%) on combination therapy 1
Routine TSH monitoring every 4-6 weeks is recommended for asymptomatic patients, with free T4 added if TSH is abnormal 1
Thyrotoxicosis from thyroiditis typically occurs one month after starting therapy, followed by hypothyroidism after another month 1
Anti-TPO antibodies help distinguish immune-related thyroiditis from other causes of thyroid dysfunction 1

Low free T4 with low or inappropriately normal TSH suggests pituitary dysfunction rather than primary thyroid disease 3, 2
Additional testing should include ACTH, cortisol, gonadal hormones (testosterone in men, estradiol in women), FSH, and LH 3
MRI of the sella with pituitary cuts is essential for diagnostic confirmation 3
Steroids must always be started before thyroid hormone in patients with both adrenal insufficiency and hypothyroidism to avoid adrenal crisis 3, 1

If TSH is abnormal, measure free T4 to distinguish subclinical from overt dysfunction 2
Add anti-TPO antibodies when TSH is elevated to confirm autoimmune etiology and predict progression risk 1, 2
Measure total T3 when evaluating thyrotoxicosis, as T3 toxicosis can occur with normal T4 1

Confirm elevated TSH with repeat testing after 3-6 weeks, as 30-60% of high TSH levels normalize spontaneously 2
Never start thyroid hormone before ruling out adrenal insufficiency in patients with suspected central hypothyroidism, as this can precipitate adrenal crisis 3, 1
Consider non-thyroidal illness, recent iodine exposure, or medications as causes of transient thyroid function test abnormalities 2