How accurate are liver funtion blood tests really?

Usually acturate. They usually are acturate esecially if you do not drink alcohol for 7 days prior to the liver function test.
Extremely. However, the interpretation is the tricky part. High liver function tests (and it's a misnomer), especially the SGPT which is specific, can result from everything from running a marathon (which shunts blood from the liver) to horrible liver disease to simply drinking too much or not exercising or taking motrin. Any physician knows how to do the workup. Good luck.