Varioskan™ ALF Multimode Microplate Reader, Standard - FAQs

Can relative fluorescence units (RFUs) be compared between two different plate readers?

Relative fluorescence units (RFUs) cannot be compared between two different microplate readers. RFU values are arbitrary and dimensionless, meaning that the actual numbers don't have a specific physical meaning, but the relative values are used for comparison. The critical measurement is the ratio of signal to background.

Whether the signal is low or high is 100% dependent on the baseline, i.e., if the sample signal is 2 and the baseline is 1, then it is a low signal but if the sample signal is 2 and the baseline is 0.01, then it is a very high signal. Instruments that typically give sample signals in the tens of thousands RFUs also typically have baseline RFUs somewhere in the tens or hundreds. For example, the Varioskan Microplate Reader is designed such that the baseline is kept below 0.1 RFU.