My serum creatinine is 0.8. what does this mean?

Serum creatinine: By itself, your serum creatinine (C) is within normal limits. C is dependent on age, sex, race and weight. As you did not mention any personal information, ask the physician (P) who ordered the test. I suspect that if there were a problem with your C level, the P would have told you and you have nothing to worry about. Good luck.