blood test- kidney levels elevated

I get monthly blood tests since I am on Methotrexate and Remicade. This month all the levels improved except my kidney which was elevated. The nurse asked if I was drinking a lot of water, and I told her I do. She said to continue to focus on drinking water and we'll see what next month's test show.

Does this mean that my kidneys are having a hard time filtering out the medication? Can it possibly have anything to do with diet? I know I probably should have asked her, but I was at work when she called.