Lab Tests for Thyroid Disorders
Thyroid disorders are among the most common endocrine conditions. The right combination of blood tests distinguishes underactive thyroid (hypothyroidism), overactive thyroid (hyperthyroidism), and autoimmune thyroid disease — each requiring different management.
Clinical overview
TSH is the pituitary hormone that controls the thyroid. It's the most sensitive signal of thyroid dysfunction and is always the first test ordered. Free T4 and anti-TPO antibodies are added to confirm the cause and guide treatment decisions.
Primary tests ordered for Thyroid Disorders
These are the tests most commonly ordered first when thyroid disorders is suspected or being monitored.
Thyroid Panel (TSH, T3, T4)
Your TSH came back outside the normal range and you've been Googling hypothyroidism vs hyperthyroidism for an hour.…
Anti-TPO Antibodies (Anti-Thyroid Peroxidase)
A positive anti-TPO result means your immune system is producing antibodies against your thyroid. It's the most common…
What to expect
- 🌅 TSH is most accurate as an early-morning draw (though not strictly required).
- ⏰ No fasting required for thyroid function tests.
- 💊 Biotin supplements suppress TSH — stop 2–3 days before testing.
- 📊 TSH is the single best screening test — T4 and antibodies are added based on results.
- 🔄 Levothyroxine dose should be taken after, not before, the blood draw.
Testing frequency
Also commonly ordered
These tests are frequently added to the primary panel based on initial results or specific clinical circumstances.
Free T3
Active thyroid hormone. Particularly useful in monitoring thyroid cancer treatment and in suspected T3 toxicosis.
TSH Receptor Antibody (TRAb)
The specific antibody causing hyperthyroidism in Graves' disease. Confirms the diagnosis.
Thyroglobulin (Tg)
Tumour marker used exclusively in thyroid cancer follow-up after thyroidectomy.
Vitamin D
Low vitamin D is common in Hashimoto's and may worsen autoimmune activity.
Complete Blood Count
Hypothyroidism causes macrocytic anaemia; hyperthyroidism can cause a mild leukocytosis.
Lipid Panel
Hypothyroidism raises LDL significantly. Lipids normalise when thyroid function is restored.
Urgent result thresholds
These result patterns require prompt clinical attention — always discuss with your doctor rather than interpreting alone.
Overt hypothyroidism — levothyroxine treatment is indicated regardless of symptoms.
Severe suppression — hyperthyroidism. Add TRAb and imaging to investigate Graves' disease.
Strongly positive — high risk of overt hypothyroidism. Monitor TSH every 6 months.
Very low T4 with high TSH — symptomatic hypothyroidism. Start treatment promptly.
Medical Disclaimer: This guide is for educational reference only. It does not constitute medical advice and should not replace consultation with a qualified healthcare professional. Always discuss your test results with your doctor. Full disclaimer →