Decoding Your Thyroid Blood Tests
You have had your thyroid tested and received a set of values that seem like alphabet soup – TSH, fT4, fT3, TPO antibodies. What do they mean? How do they relate to how you feel? At our practice in Zürich Seefeld, I run comprehensive thyroid panels and take the time to explain what each value means and why it matters.
The Thyroid Hormones
TSH (Thyroid Stimulating Hormone): Produced by the pituitary gland, TSH tells the thyroid how much hormone to produce. When thyroid hormones are low, TSH rises (hypothyroidism). When thyroid hormones are high, TSH falls (hyperthyroidism). TSH is the most sensitive screening test, but it only tells you what the pituitary thinks – not what the thyroid is actually producing or what your cells are receiving.
Free T4 (Thyroxine): The main hormone produced by the thyroid gland. T4 is the “storage” form – it must be converted to T3 to become active. Free T4 measures the biologically available portion (not bound to proteins).
Free T3 (Triiodothyronine): The active thyroid hormone. T3 is what actually enters cells and drives metabolic function. Most T3 is converted from T4 in peripheral tissues (liver, gut, muscles). Low fT3 with normal fT4 and TSH can indicate poor conversion – a situation that TSH screening alone would miss.
Reverse T3 (rT3): An inactive form of T3. When the body is under stress, instead of converting T4 to active T3, it produces reverse T3. This is the body’s “brake” on metabolism during illness, starvation, or chronic stress. Elevated rT3 with normal TSH can explain symptoms of hypothyroidism despite “normal” standard tests.
Thyroid Antibodies
TPO Antibodies (Anti-Thyroid Peroxidase): Elevated in Hashimoto’s thyroiditis and sometimes in Graves’ disease. Their presence indicates autoimmune thyroid disease, which may cause symptoms years before TSH becomes abnormal.
Thyroglobulin Antibodies: Also associated with Hashimoto’s. Some patients have elevated thyroglobulin antibodies but normal TPO antibodies.
TSI (Thyroid Stimulating Immunoglobulins): Specific to Graves’ disease. These antibodies stimulate the thyroid to overproduce hormones.
Why I Test More Than Just TSH
Standard thyroid screening checks TSH only. If TSH is within the reference range (typically 0.4-4.0 mIU/L), the thyroid is declared “normal.” But this misses several clinically important situations: subclinical hypothyroidism with symptoms, poor T4-to-T3 conversion, elevated reverse T3 from chronic stress, Hashimoto’s with normal TSH but elevated antibodies, and central hypothyroidism (pituitary dysfunction). I run a complete panel: TSH, fT4, fT3, rT3, TPO antibodies, and thyroglobulin antibodies.
Optimal vs. Normal Ranges
Laboratory reference ranges are statistically derived – they represent where 95% of the tested population falls. But “normal” includes people with undiagnosed thyroid disease. I consider TSH optimal between 1.0-2.5 mIU/L (not just “in range”), fT3 and fT4 in the upper half of the reference range, and any antibody elevation as clinically significant.
What We Do: Comprehensive Thyroid Care
Complete thyroid panel: TSH, fT4, fT3, rT3, and antibodies for a full picture.
Clinical correlation: Interpreting results alongside your symptoms, not just numbers on paper.
Nutrient assessment: Iron, selenium, zinc, vitamin D, and iodine – all essential for thyroid function and hormone conversion.
Individualised treatment: If treatment is indicated, finding the right medication and dose for your specific situation.
Conclusion
Your thyroid values tell a story – but only if the right tests are done and interpreted in context. If you have thyroid symptoms but have been told your TSH is “normal,” a comprehensive panel may reveal the full picture. Book a thyroid evaluation at our practice in Zürich Seefeld.
