Thanks for all the comments guys. The red urine was one time only. The samples before and after were light yellow. No pain while urinating as one might suspect if it was a bladder infection. I actually attributed the red colour more to the fact that I had blueberries the night before rather than another specific issue. I continued on with my plans today and had no problems whatsoever - I made extra sure of hydrating myself. No other health problems, no drugs, no previous issues with donating blood (42 donations to date), etc. However, I am not 100% convinced that it was a simply case of dehydration either as I did not experience a headache as normally would be the case. If this was a related to a gastronomical bug, it was in and out and through with me really quick because I am feeling fine.