Hi how much does alt (sgpt) fluctuate? i had a reading of 40u/l then 2 days later 41u/l is this increasing ? or would it be a lot higher if it were? thank you?

Those values are considered the same. Mild fluctuations up/down by 10% are not unusual & might be seen in the same specimen tested the same day. Go from 40's to 100's a few days apart & I would expect something worrisome to be triggering the change.

The change you described is not clinically meaningful. Talk to the doctor who ordered the test as all laboratory results need to be interpreted in the clinical context.