Comprehensive Thyroid Assessment
Fatigue, mood swings, weight changes and palpitations are often blamed on stress or age — yet the cause can be the thyroid gland. This calculator brings together the hormones (TSH, free T4 and T3), antibodies and calculated indices (TSHI, free T3/free T4, SPINA-GT and SPINA-GD) to catch hidden problems that a single TSH would miss.
Why TSH alone isn't the whole picture
Thyroid function is usually assessed by TSH. But a normal TSH doesn't rule out a problem: there can be reduced T4 → T3 conversion, autoimmune activity (antibodies appear years before TSH shifts), or impaired pituitary sensitivity. To see this you need the full profile: the hormones themselves, antibodies and calculated indices that describe how the pituitary–gland–tissue axis works as a whole.
Thyroid function calculator
Enter the values from your blood test. TSH, free T4 and free T3 are required; antibodies are optional (they refine the autoimmune picture). The calculation runs on the server and the data is not stored.
What the calculated indices mean
| Index | What it assesses | Normal |
|---|---|---|
| TSHI | Central sensitivity: whether TSH is appropriate for the free T4 level (the pituitary–gland axis) | 1.35–3.71 |
| Free T3 / Free T4 | Peripheral conversion of T4 into active T3 | 0.29–0.38 |
| SPINA-GD | The total activity of the deiodinases (T4 → T3 conversion) | 20–40 nmol/s |
| SPINA-GT | Secretory capacity of the gland (maximum thyroxine output) | 1.4–8.7 pmol/s |
Optimal and reference ranges
The standard reference range is “where most people fall,” while the optimum is where people usually feel best. A value can be “within normal limits” yet outside the optimum — and that is exactly the zone of hidden dysfunction.
| Marker | Reference | Optimal |
|---|---|---|
| TSH, mIU/L | 0.3–4.0 | 0.5–2.5 |
| Free T4, ng/dL | 0.8–1.8 | 1.4–1.7 |
| Free T3, pg/mL | 2.3–6.2 | 3.8–4.4 |
| Anti-TPO, IU/mL | 0–34 | not detectable |
| Anti-Tg, IU/mL | 0–0.9 | not detectable |
Antibodies: an early signal of autoimmune problems
Anti-TPO and anti-Tg can rise years before TSH becomes abnormal — the earliest sign of Hashimoto's thyroiditis. TRAb (antibodies against the TSH receptor) are specific to Graves' disease. Even with “normal” hormones, elevated antibodies mean a higher risk of future dysfunction and a reason to monitor gland function over time.
How to support your thyroid
General principles: enough iodine and selenium (but not in excess), managing stress and sleep (cortisol slows T4→T3 conversion), treating iron and vitamin D deficiencies, and quitting smoking. If there are abnormalities, don't self-medicate: the dose and approach are set by an endocrinologist. The lifestyle calculator helps gauge your overall metabolic background.
Frequently asked questions
My TSH is normal but I feel unwell — why?
A common reason is a low free T3 or poor T4-to-T3 conversion despite a normal TSH. That is exactly why it's important to look at free T3, the free T3/free T4 ratio and the SPINA indices, not just TSH.
Do I have to enter antibodies?
No, the calculation works without them. But antibodies refine the autoimmune picture (Hashimoto's, Graves') and are useful if they have been measured for you.
How is this different from the thyroid function calculator?
The function calculator gives a basic assessment of TSH/T4/T3. This one is comprehensive: plus antibodies and calculated indices of central sensitivity, conversion and secretion. For symptoms without lab tests there is a symptom-based screening.
My units are different (pmol/L). What should I do?
Convert before entering: free T4 (pmol/L) ÷ 12.87 = ng/dL; free T3 (pmol/L) ÷ 1.536 = pg/mL. TSH is almost always in mIU/L.
