Thyroid Test Checker
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The Hypothalamic-Pituitary-Thyroid Axis
Thyroid function is controlled by a feedback loop. When circulating levels of thyroid hormones (T4 and T3) drop, the pituitary gland releases more TSH to stimulate the thyroid. When hormone levels are high, TSH release is suppressed. Consequently, TSH is the most sensitive screening test for thyroid function.
Understanding Thyroid Panel Patterns
Common patterns include Primary Hypothyroidism (high TSH, low Free T4), Primary Hyperthyroidism (low TSH, high Free T4 or T3), Subclinical Hypothyroidism (mildly high TSH with normal Free T4), and Subclinical Hyperthyroidism (mildly low TSH with normal Free T4).
Factors That Interfere with Thyroid Tests
Biotin supplements (commonly found in hair, skin, and nail products) can cause falsely elevated T3/T4 and falsely low TSH. Clinicians typically recommend discussing biotin intake with your provider, who may advise pausing biotin supplements for 48 to 72 hours before a thyroid blood test. Severe illness or pregnancy can also affect results.
When to Seek Urgent Medical Attention
- Severely elevated thyroid hormone levels accompanied by high fever, confusion, rapid heart rate, or severe agitation (Thyroid Storm).
- Abnormally low thyroid levels accompanied by low body temperature, severe lethargy, or swelling (Myxedema Crisis).
Frequently Asked Questions
TSH is produced by the pituitary gland to signal the thyroid gland to release hormones. Paradoxically, high TSH suggests an underactive thyroid, while low TSH suggests an overactive thyroid.
Hypothyroidism is an underactive thyroid causing symptoms like fatigue and cold intolerance. Hyperthyroidism is an overactive thyroid causing rapid heart rate, weight loss, and anxiety.
