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What meter where you using before?

Choice will depend upon what is more important, accuracy or precission!

If you want accuracy and precission to 0.1uA you are into 4.5 digit UKAL calibrated meters, which will set you back several hundred pounds.

I doubt this is what you are looking for though!

I have several 4.5 digit bench multimeters which will give you the precision to 0.1uA but not the accuracy of a calibration to 0.1uA.

Ask yourself how critical is your need to measure 37.5uA. That will dictate the standard of meter you will require.