TSH: place my value

What moves the bounds for TSH

• Age: TSH rises naturally over the years. In an older person, a value this tool places in the disagreement band may be considered usual for their age.
• Pregnancy: the bounds are different and specific to each trimester. The interval used here is the non-pregnant adult one — it does not apply to a pregnant woman.
• Time of the draw: TSH follows a twenty-four-hour rhythm, higher in the late night and early morning, lower in the afternoon. Two samples taken on the same day can differ noticeably.
• Biotin: this supplement, often taken for hair and nails, interferes with the assay used by many laboratories. Stopping it a few days before the blood draw is usually requested.
• The laboratory itself: every analyser has its own bounds, validated on its own reference population. The interval printed on your report takes precedence over any value found online, including on this page.

Frequently asked questions

What is a normal TSH level?

There is no single value. Most laboratories use an adult interval running from 0.5 to 4.0 mU/L, some pushing the upper bound to 5.0. The interval printed next to your result is the one that applies to your measurement: it was validated on that particular laboratory's assay and reference population.

What exactly is TSH?

TSH, or thyroid-stimulating hormone, is not a thyroid hormone: it is the hormone the pituitary produces to drive the thyroid. When the thyroid produces little, the pituitary raises TSH to stimulate it; when it produces a lot, TSH falls. The relationship is therefore inverted — a high TSH corresponds to a thyroid doing little work — which is what makes this marker counter-intuitive to read.

mU/L, mIU/L, µIU/mL: what is the difference?

None. These are different notations of the same unit, in a one-to-one ratio. A TSH of 2.3 mU/L is exactly a TSH of 2.3 µIU/mL. Your value does not change with the notation your laboratory chose, and the unit selector in this tool only changes what is displayed.

What is an ultra-sensitive TSH?

That is the name of the assay technique, not a different test. Current analysers detect very low concentrations, which makes it possible to tell a suppressed TSH from a merely low one. “TSH us”, “ultra-sensitive TSH” and “TSH” refer to the same measurement today and are read against the same interval.

My TSH is 4.5 — is that high?

It depends on the laboratory. 4.5 mU/L falls exactly in the band where bounds diverge: above the limit for a laboratory stopping at 4.0, inside the interval for one going to 5.0. This is the situation that most often leads to a re-check a few weeks later rather than an immediate conclusion. A single number is not enough.

Do you need to fast for a TSH test?

A TSH measurement does not require fasting. The time of day does matter, though: TSH is higher early in the morning and lower in the afternoon. To compare two measurements over time, it is better to take them at a comparable hour.