Post vet confusion about elevated ALTs

I took my dog in for a routine annual visit, he is a three year 3 month mix of Australian shepherd and Newfoundland (50/50 mix). To my surprise and the vets surprise his ALT was 530 and from my understanding she said it’s usually below 120. Other than that his blood test was unremarkable and we just got back today where they reported his abdominal ultrasound is normal. We moved from a cooler environment to a warmer environment and into an apartment so my dog has had less exercise (part due to heat, part due to small living space, and yes of course part my fault). When he was neutered in March of this year he weighed 81 lbs and now he is 104. My vet is thinking this is mostly due to too many treats (everybody loves him at the apartment) and decreased exercise and not related to the liver. The vet said she want to be conservative and start medication to help his liver get healthier (I don’t have the name but it started with a D) plus also possibly amoxicillin and another drug used to treat bacterial hepatitis in case that’s what it is. Her thought is that it could be chronic hepatitis (he was diagnosed with gastritis at 2 by a different vet with only a basic CBC test done and going off the symptoms of weight loss, diarrhea, vomiting, and anorexia and thinks perhaps he was misdiagnosed) but she cannot confirm without a biopsy which we agreed to hold off on and try medication and recheck blood first due to the high risk. My questions are … does chronic hepatitis seem to fit? What causes that to appear at such a young age? Should I be doing anything else? Could it be something else ??

Hello!   ALT is very sensitive to an extra load going on the liver  - certain foods being digested, therapeutic drugs (including some types of antibiotics! - alcohol's a biggy for humans), extra hard work that the body has been doing recently, a higher metabolic rate due to thyroid disease..... and so on.  A lot of the time, when the pressure goes off the liver again, the ALT will drop spontaneously.  Most of these rises and falls we wouldn't even be aware of, unless we happened to test the liver.  If we see an elevation and go back and test again a few weeks later, we often find that the values are resolving (rarely, they are going up fast and we know that we need to investigate, quickly).  However, some animals seem to have persistently elevated liver enzymes - in these instances, one explanation is that the liver could be inflamed.  It is definitely a common practice to give a supplement containing chemicals that may help the liver along, and then to test again.  Sometimes special diets are employed that are designed to be kind to the liver tissue.   https://vethelpdirect.com/vetblog/2022/07/23/why-should-i-feed-a-dog-with-liver-problems-a-special-diet/  When the liver levels are persistently affected, vets do tend to want to know why - could there be cancer or fibrosis of the liver, or a breed-related illness or inflammatory disease going on - and a biopsy is generally taken in order to tell them more, putting them in the best position to help the pet. The level at which this is investigated is always a matter of debate - as a vet, I usually ask for guidance from the pathologist who would normally look at the biopsy I was about to take.  These people see all of the samples and histories that come in, including the preliminary blood tests, and usefully advise me regarding what to do in order to get the best outcome for the least invasive tests.  If a case if border-line or I do not know what to expect, I often find that this can add value.