How to Read Your Thyroid Panel: TSH, Free T4, and Free T3

Your thyroid panel tells you how well your body's metabolic thermostat is working — and reading TSH, free T4, and free T3 together (rather than TSH alone) is the key to understanding symptoms like fatigue, weight change, and low mood.

The thyroid sets your metabolic pace. A panel usually includes TSH (the pituitary's signal to the thyroid), the thyroid hormones free T4 and free T3, and sometimes antibodies. This is educational content, not medical advice.

The short version

• TSH is the screening test: ~0.4–4.0 mIU/L is a common normal range.

• A high TSH suggests an underactive thyroid (hypothyroid); a low TSH suggests an overactive one (hyperthyroid).

• Free T4 and free T3 measure the actual thyroid hormones; TPO antibodies flag autoimmune thyroid disease (Hashimoto's).

• TSH alone can miss the picture — the markers are best read together, with symptoms.

What the numbers mean

Because TSH rises when the thyroid is underperforming, it moves opposite to thyroid hormone. TSH above ~4.0 with low free T4 points toward hypothyroidism (fatigue, weight gain, cold intolerance, low mood). TSH below ~0.4 with high free hormones points toward hyperthyroidism (anxiety, palpitations, weight loss). Mildly abnormal TSH with normal free hormones is "subclinical" and needs clinical judgment. Reference ranges vary by lab, so read yours in context.

Why read them together

TSH is sensitive but not the whole story. Free T4 and free T3 show how much active hormone you actually have, and TPO antibodies reveal whether an autoimmune process (the most common cause of hypothyroidism) is underway. Thyroid symptoms also overlap with other conditions — including adrenal and stress-related patterns, which is why some clinicians assess it alongside markers like cortisol.

What to do

Interpretation and treatment belong with a clinician. Depending on the pattern, that might mean monitoring, thyroid hormone replacement, or further workup for autoimmune or nodular disease. Don't self-treat thyroid symptoms with supplements or hormones.

Which provider and what to ask

Primary care and endocrinology handle this. Ask: Do my TSH and free hormones agree? Should we check TPO antibodies? Are my symptoms consistent with my labs?

Frequently asked questions

What is a normal TSH?
Commonly ~0.4–4.0 mIU/L, though labs differ and optimal targets are debated.

Can I have thyroid symptoms with a normal TSH?
Sometimes — which is why free T4/T3 and antibodies can add information.

Do I need to fast?
Not required, though timing and biotin supplements can affect results — follow your lab's guidance.

Key takeaways

• TSH (~0.4–4.0) is the screen; high suggests underactive, low suggests overactive.

• Free T4, free T3, and TPO antibodies complete the picture.

• Read the panel together, with symptoms, guided by a clinician.

Understand your thyroid results

Sidewalk can help you interpret your panel and find a provider who takes thyroid symptoms seriously. Complete a free AI health assessment or find a provider.

This article is for educational purposes only and is not a substitute for professional medical advice.