For some ELISA based antibody tests (e.g. h-tTg antibody test), labs report units as RU/mL or U/mL. Also different labs have different cut off (normal range) values.
I understand that different kit manufacturers recommend different ranges because the units are not standardized (e.g. IU/mL) for enzyme activity concerned. But I didn't understand the difference between RU, U and AU
Question Is there a difference between RU/mL, AU/mL and U/mL? Are the figures comparable across reports from different labs (which may be using different kits)?