TSH levels by number

A TSH result is easy to look up and hard to interpret, because the same number means different things depending on where it falls. The usual adult reference range is roughly 0.4 to 4 mIU/L, and treatment for an underactive thyroid is typically considered above 10 mIU/L — but the interesting territory is everything in between.

Pick your value below. Each page covers what that specific level means, what tends to cause it, whether treatment is usually indicated, and which tests belong alongside it. If your exact number isn't listed, the nearest one will read the same way.

Effectively undetectable

0 – 0.03 mIU/L · at the very floor of what an assay can measure

• TSH 0.01

Deeply suppressed

0.03 – 0.1 mIU/L · far below the reference range

• TSH 0.05

Clearly below range

0.1 – 0.3 mIU/L · below the reference range

• TSH 0.1

Just below range

0.3 – 0.4 mIU/L · a shade under the reference range

• TSH 0.3

Low end of normal

0.4 – 1 mIU/L · in the lower part of the normal range

• TSH 0.5

Mid-normal

1 – 2 mIU/L · squarely in the middle of the normal range

• TSH 1.5

Upper-middle of normal

2 – 2.6 mIU/L · normal, just above the midpoint

• TSH 2.5

High-normal

2.6 – 3.6 mIU/L · in the upper part of the normal range

• TSH 3.5

Top of the normal range

3.6 – 4 mIU/L · at the very top of the normal range

• TSH 3.9

Just above the reference range

4 – 5 mIU/L · just above the reference range

• TSH 4.8

Mild subclinical hypothyroidism

5 – 7 mIU/L · clearly above the reference range

• TSH 5.5

Approaching the treatment threshold

7 – 10 mIU/L · well above the reference range

• TSH 8.8

Overt hypothyroidism range

10 – 20 mIU/L · past the usual treatment threshold

• TSH 11

Marked hypothyroidism

20 – 45 mIU/L · many times the upper limit

• TSH 30

Severe hypothyroidism

Above 45 mIU/L · extremely high

• TSH 100

Reading a TSH result properly

TSH runs opposite to thyroid output: it rises when the thyroid underperforms and falls when it overperforms. That's why a high TSH means an underactive thyroid, which catches most people out. For the mechanism, start with what a high TSH is actually telling you, and for the hormones TSH is regulating, see free T3 and free T4 explained.

Two caveats apply to every value on this page. Reference ranges differ between laboratories, so compare against the range printed on your own report rather than a range from the internet. And single readings fluctuate — TSH peaks overnight, shifts with illness, and responds slowly to real change, so the trend across several tests carries more information than any one result.

Related guides

• High TSH: what your thyroid is actually telling you
• What causes high TSH
• High TSH symptoms
• High TSH with high T4
• TSH over 100
• Hyperthyroidism and TSH
• Ultrasensitive TSH explained
• Thyroid antibodies (TPO)

This page is for education and isn't medical advice. Discuss your results with a qualified clinician.