To check your liver, they check something called transaminases..if these are elevated, it usually means your liver is inflamed. Depending on which ones are elevated, it could mean that the actual liver tissue is sick and that's why your liver is inflamed, or there is something blocking your liver's ducts, and that's why it's inflamed. The enzymes are AST, ALT and GGT. Usually, if the first two are high and the third one isn't, it means your liver tissue is actually sick....if only GGT is high, usually it means a stone or something.
Other tests for liver function include total albumin (the liver produces proteins) and also something called INR (international normalized ratio) which is a test to see how fast your blood clots. The liver produces vitamin K dependent clotting factors (II, VII, IX & X), so if the liver is sick, these won't be produced as effectively and your INR will be higher.
Things that can cause hepatitis (i.e. inflamed liver) are hepatitis viruses, systemic diseases, lipid dystrophies (problems producing lipids), certain drugs, alcohol....etc. (this list is by NO means exhaustive)
Someone mentioned "fatty liver". Most of us who drink at all will have some type of fatty liver, which is not necessarily a bad thing because it goes away once you stop drinking. There is something called NASH (non alcoholic steatohepatitis) which is a fatty liver inflammation in a person who claims to not drink at all. It isn't very common, but it can happen. I'm not sure if you necessarily need a biopsy just yet (it also depends on how aggressively the center that you will be treated at, treats its patients). I'm curious to hear the results of your liver screen. Let us know!