ALT of 40 is right around the upper limit of the normal range set by most labs, & moderate elevations are common in obese populations. Doctors usually don't sweat a minor/isolated elevation unless it is double or more the upper limit of the normal range.
If 40 is at all higher than the upper limit set by your lab, then a retest, typically between 90 days and 6 months should be justified. If you're just within normal, then your doc is probably correct in saying a retest in not "required". An isolated lab elevation probably would not justify additional diagnostics at this time, but if you're still out of range on a retest, then additional diagnostics may be warranted.
Personally, I'd like to try for a retest at around 6 months, after attempting to improve diet & weight loss, to see if ALT is trending lower, hanging high, or trending upwards. Perhaps if you leave it be with your doc for now, he/she will be more receptive to followup labs at around 6 months.
Well done on the no alcohol bit- that lessens the chances of further damage if you’re overweight. Concentrate on the weight loss and most things should fall into place- know it’s difficult but persevere. It’s not just the liver that will improve!
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