TSH
What it measures
µIU/mL and mIU/L are the same magnitude under different names — not a true unit conversion, just two labels for one scale — while mIU/mL (note the second 'm', not µ) is thousands of times larger and easy to misread if a report is copied without care.
TSH — why your lab's range is the one that counts
| Laboratory | Value |
|---|---|
| Quest Diagnostics, age 20+ | 0.40 – 4.50 mIU/L |
| Labcorp, age above 10 | 0.450 – 4.500 µIU/mL |
Two large laboratories, two different intervals — and that is the point. TSH is not fully standardised across manufacturers: antibodies in different assays bind different parts of the molecule, so two analysers can return meaningfully different numbers from the same tube of blood. TSH also swings through the day, shifts with age, and moves with iodine intake, smoking and several medicines. The interval printed beside your result, by the lab that ran it, is the one to read it against — not a number from a website, including this one. In pregnancy the intervals change again by trimester.
Reading it in a different unit
This lab reports TSH in uiu/ml. Reports from other labs — especially ones using European or US-style formatting — sometimes use a different unit for the same measurement. The relationship between them:
miu/l is the same value as uiu/ml under a different name — nothing to calculate, just a different label on the same number.
| Reported unit | How it relates to uiu/ml |
|---|---|
| miu/ml | uiu/ml = miu/ml × 1000 |
Unit conversions verified against published molar masses and LOINC definitions. This is not a diagnostic reference — the normal range for any test is set by the laboratory that ran it and printed on your report.
Why this matters for tracking a trend
A value plotted next to earlier results only tells you something if every point is on the same scale. Two readings of the same test from two different labs, in two different units, can look like a dramatic change when nothing about your actual result changed — only the unit did. Converting to one scale before comparing is what keeps a trend line honest.
LOINC codes for this test: 11579-0, 3016-3.
General information about laboratory measurement, not medical advice. Whether a specific result is normal for you depends on your lab's reference range, your history and your doctor's judgement — not on this page.