Interpreting the Thyroid Panel
| TSH | Free T4 | Free T3 | Interpretation |
|---|---|---|---|
| High | Low | Low | Overt (primary) hypothyroidism |
| High | Normal | Normal | Subclinical hypothyroidism |
| Low | High | High | Overt hyperthyroidism |
| Low | Normal | Normal | Subclinical hyperthyroidism |
| Low | Low | Low | Secondary (central) hypothyroidism — pituitary failure |
| Normal | Normal | Normal | Euthyroid (normal thyroid function) |
Causes by Pattern
| Pattern | Most Likely Cause |
|---|---|
| Overt hypothyroidism | Hashimoto's thyroiditis, post-thyroidectomy, post-radioiodine, drug-induced (amiodarone, lithium) |
| Subclinical hypothyroidism | Early Hashimoto's, thyroiditis, iodine deficiency |
| Overt hyperthyroidism | Graves' disease, toxic nodule, toxic multinodular goitre |
| Subclinical hyperthyroidism | Early Graves', exogenous thyroid hormone overtreatment |
| Low TSH + low T4 | Pituitary adenoma, Sheehan's syndrome, inflammatory hypophysitis |
TSH Is the Screening TestStart with TSH. If normal, thyroid function is almost certainly normal. Only add Free T4 and T3 if TSH is abnormal. This avoids unnecessary cascade testing.
What TSH level needs treatment?
Overt hypothyroidism (high TSH + low T4) always needs levothyroxine. Subclinical hypothyroidism (TSH 4–10 with normal T4) is treated if: TSH >10, symptomatic, pregnant, planning pregnancy, or TPO-antibody positive.
Why is my TSH high despite taking levothyroxine?
Most commonly: non-compliance, dose timing issues (should be taken 30–60 min before food), malabsorption, or drug interactions (calcium, iron, PPIs). Dose may also simply need increasing.
Can stress affect thyroid tests?
Acute illness or stress can cause non-thyroidal illness syndrome (sick euthyroid syndrome) — TSH and T4 can be low during acute illness without true thyroid disease. Retest 4–6 weeks after recovery.
What is subclinical hypothyroidism?
High TSH with normal Free T4. The thyroid is working harder to maintain normal hormone output. Risk of progression to overt hypothyroidism is ~5% per year, higher if TPO antibodies are positive.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.