FUJIFILM Irvine Scientific

International Unit Conversion

Technical Support

International Unit Conversion

The table below provides data for the conversion of the indicated products.

International Units (Us/ug) for Cytokines by FUJIFILM Irvine Scientific


International units (IU) are used for the determination of biological material in a consistent internationally agreed manner.  The World Health Organization (WHO) is a source for protein reference standards of defined biological activity that are accessible to everyone. The National Institute for Biological Standards and Control (NIBSC) distributes these materials.

In general, the reference standard of a protein is defined by the number of units per mass of material, also known as reference units (RU). If the reference material has been tested in a multi-center, international, collaborative study, it is designated as international units (IU) by the WHO. Where available, FUJIFILM Irvine Scientific tests our products against the appropriate reference standard to allow for the direct conversion of mass to units.

Testing for potency, and reporting IUs/ug, puts FUJIFILM Irvine Scientific among the highest level of cytokine and growth factor manufacturers in the market.


FUJIFILM Irvine Scientific is taking steps to offer our customers 100% transparency with our QA. One of these steps is to list the minimum acceptance criteria so that our customers can be assured of the quality they are purchasing. FUJIFILM Irvine Scientific’s acceptance criteria is set using internal bioassay data in combination with self-reported “typical” ranges and acceptance criteria of our competitors. It is important to note when comparing the two, a “typical” range and an acceptance criteria limit are not equal.  Shenandoah’s results are most often much lower than the acceptance criteria set.  When this is the case, the “typical expected range” will be published on our website as well.

The ED50 is an expression of activity at 50% of its maximum response. Specific activity is just another way of conveying the activity of the protein. To calculate a specific activity, divide 1 x 10^6 by the ED50 in ng/ml.  

Specific Activity (Units/mg) = 1 x 10^6 / ED50 (ng/ml)

For some proteins (mainly viral CPE assays), the specific activity is the only number calculated.  For other assays that are more qualitative in nature (chemotaxis and western blotting for phospho-proteins), specific activity is not a relavant way of communicating activity.  

No.  International Units are calculated using a validated assay where the cytokine in question is tested side-by-side with an internal standard set by the WHO.  The activity of the cytokine in question is then normalized to the activity level of the standard.  

Select cytokines are run side-by-side with an international standard (IS) and this data is indicated for each of these products. 

Products tested against IS:
Human IL-2
Human IL-3
Human IL-15
Mouse IL-2

For those products that are not compared to IS, the data reported on our documents are considered “in-house-units” and are routinely run side-by-side with competitors from the recombinant protein market, but cannot be compared to other assays directly.  Even if the same cell line is used, there are still factors that will differ from lab to lab, and comparability of results can vary.


Our products are used for many different purposes, so it would be impossible to predict every possible application. Our standard bioassay is used to confirm an accepted activity level for the product. Our proteins can be used at a broad concentration range, in many different applications, thus, it is the end user’s responsibility to determine the concentrations that work best for their specific assays.

Although many human cytokines will respond nicely in mouse cell lines, and many mouse proteins will show activity on human cells, species cross-reactivity must be investigated individually for each product