TSH
The thyroid's thermostat signal. TSH (Thyroid Stimulating Hormone) is released by the pituitary to tell the thyroid to produce more hormones. High TSH means the thyroid isn't responding—hypothyroid. Low TSH means too much thyroid hormone—hyperthyroid. But "normal" ranges are debated.
Understanding TSH
Inverse Relationship
High TSH = LOW thyroid function. Pituitary is screaming for more. Confusing but important.
Negative Feedback
When T3/T4 are high, TSH drops. When low, TSH rises. Like a thermostat.
Lab Ranges Too Wide
Standard 0.5-4.5 includes subclinical dysfunction. Many feel better 0.5-2.5.
Not Complete Picture
TSH alone misses conversion issues. Need Free T4, Free T3, and antibodies.
Morning Best
TSH highest in morning, lowest afternoon. Consistent timing matters for tracking.
Interpreting TSH Levels
High TSH (> 4.5)
Hypothyroid. Thyroid underperforming. Pituitary pushing hard. Symptoms likely.
Slightly High (2.5-4.5)
Subclinical hypothyroid. "Normal" but not optimal. Often symptomatic.
Optimal (0.5-2.5)
Where most feel best. Functional range. Target for treatment.
Low (< 0.5)
Hyperthyroid possible. Too much thyroid hormone. Or over-medicated.
Suppressed (< 0.1)
Very low. Graves' disease or over-treatment. Needs investigation.
Complete Thyroid Panel
TSH
Pituitary signal. Starting point but not complete.
Free T4
Storage hormone. What thyroid produces. Must convert to T3.
Free T3
Active hormone. What cells actually use. Often not tested but crucial.
Reverse T3
Inactive form. High in stress, illness. Blocks T3 receptors.
TPO Antibodies
Hashimoto's marker. Autoimmune thyroid. Common cause of hypo.
TG Antibodies
Thyroglobulin antibodies. Additional autoimmune marker.