How do I reduce the amount of ceatinine showing in my blood tests?

Meat contains high levels of creatinine, so a vegetarian diet automatically helps to reduce raised serum creatinine levels.

Some Ayurvedic herbal treatment centres advocate chewing 7 leaves of the plant Vinca rosea, daily.

The plant Urtica semen (dioica), commonly called stinging nettles, has also been shown to be of help (ref: Jonathan Treasure)

Another ref about Urtica plant:
Treasure, J. 2003. Urtica semen reduces serum creatinine levels. J.AHG 4:22-25