I'm using the MP Biomedicals TSH RIA and noticed the units on the standards are uIU/mL. All of the other hormone assays I run express concentrations in ng/mL or pg/mL. I went through the the wildlife endocrinology literature and found that it was pretty split on how researchers expressed TSH. After some online exploring, I found a conversion for uIU/mL TSH to ng/mL, but there was no explanation or citation for this conversion (see attached PDF). So, with all of that in mind, my questions are, what is the accepted way to express TSH concentration AND does anyone have an explanation of the conversion factor?
- For example the WHO Expert Committee on Biological Standardization has defined the IU for TSH as "the activity contained in 36,6 mg of the International Reference Preparation DOI: 10.3109/00365519109104600
Hi
This article has a good answer for this question:
https://doi.org/10.3109/00365519109104600
In short - you cannot really convert them very easily. IU/ml of TSH shows activity of "molecularly heterogeneous" system. ng/ml isn't a unit you could use to measure something like that. There is and international standard (created by WHO, as mentioned in the previous answer; 1 IU = 36.6 mg of reference preparation) that are used to calibrate the assays and relate the result to specific amount of activity.
Also, read the chapter "The expression of comparative assay results" in the article I referenced. This 1 IU = 36.6 mg is somewhat of a simplification!
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