Enzyme activity: converting U/L, IU/L and µkat/L
What is measured
For enzymes the activity is measured, not the amount: how much substrate the enzyme converts per time. One unit (U) converts one micromole per minute; U/L and IU/L are the same. The katal (kat) is the SI unit and converts one mole per second.
The factor of 60
1 µkat/L equals 60 U/L, and 1 U/L equals 0.01667 µkat/L. Example: 0.5 µkat/L is 30 U/L; 40 U/L is 0.67 µkat/L.
Why ranges differ
The measured activity depends on the method, the substrate and the measuring temperature (for example 30 or 37 °C). Two laboratories can therefore report different numbers and ranges for the same sample. Compare trends in the same laboratory where possible.