Can you tell me in a poor pt with epigastric pain of 4 days,if you had to order just one test,which would you choose- amylase or lipase?

Depends: If the suspicion was for pancreatitis, I would choose lipase. But the choice would depend on your history, physical findings and any other data that may be available.

Either: I think lipase is more sensitive for acute pancreatitis. The amylase will always be elevated with acute pancreatitis (early on) but can also be elevated in other conditions. You can also get an elevated lipase in the absence of acute pancreatitis.