What does it mean if my ldh blood level is 355?

Non-specific. Ldh rises in many conditions. Depending on the lab, 355 is often a very mild elevation. There are 5 varieties (iso-enzymes) of ldh. Depending on which one is elevated, it could be pointing toward a problem with your (1)heart, (2)blood (3) lung, (4)pancreas/kidney or (5)liver/skeletal muscle. To determine the origin, you need a breakdown of the ldh or other blood tests.