What does a high TSH mean?

A TSH above the usual range can be associated with an underactive thyroid (hypothyroidism), as the body signals the thyroid to work harder, but it can also occur for other reasons. It needs to be interpreted by a doctor alongside thyroid hormone levels and your symptoms before any conclusion is drawn.

What does a low TSH mean?

A TSH below the usual range can be associated with an overactive thyroid (hyperthyroidism), but it can also occur for other reasons, including certain medicines and conditions. A doctor interprets it together with your thyroid hormone levels and symptoms rather than from the TSH value alone.

Is this tool a diagnosis?

No. This tool is for general education only. It shows where a TSH value falls within a commonly used reference range but does not diagnose any condition. Thyroid results must be interpreted by a doctor, who considers your full thyroid panel, symptoms, history and the specific reference range from your laboratory.

Lab Results & Test InterpretationGlobal

TSH (Thyroid) Level Interpreter

Understand where your thyroid-stimulating hormone (TSH) result falls within general reference ranges.

Written byAikins Apreku

Reviewed byDeborah Adotso, General Nurse

Updated June 2026

Your TSH level (mIU/L)

Found on your thyroid blood test result, usually labelled TSH. Units are typically mIU/L (same as µIU/mL).

What this tool does

This tool shows where your thyroid-stimulating hormone (TSH) result falls within a commonly used reference range, and explains in general terms what that area typically means. It is an educational reference tool, not a diagnosis. TSH reference ranges vary between laboratories and circumstances, and your result must be interpreted by a doctor alongside your thyroid hormone levels, symptoms and history.

About TSH

TSH is a hormone produced by the pituitary gland that signals the thyroid to make thyroid hormone. It is one of the main blood tests used to assess thyroid function. A higher TSH can suggest the thyroid is underactive (the body is signalling it to work harder), while a lower TSH can suggest it is overactive. However, interpretation is not as simple as a single number, which is why a doctor considers the full picture.

Frequently Asked Questions

A commonly used reference range for TSH is roughly 0.4 to 4.0 mIU/L, but ranges vary between laboratories and situations such as pregnancy. The range printed on your own result is the one that applies to you. TSH is also interpreted alongside thyroid hormone levels, so a doctor's assessment is needed rather than the number alone.

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Sources & References

LifeCheckIQ content is based on peer-reviewed research, recognised clinical guidelines, and authoritative medical sources, and is reviewed by Deborah Adotso, General Nurse, for clinical accuracy.

Medical Disclaimer: This tool is for informational and educational purposes only. Results are not a medical diagnosis. Always consult a qualified healthcare professional for medical advice, diagnosis, or treatment. In an emergency, call your local emergency number or visit the nearest hospital immediately.