Should I up my calories on days I donate plasma?

I would say up your calories a little bit, maybe eat an extra 200 or so? Replacing all that plasma will take some energy, and you don't want to risk feeling bad. You could ask a nurse next time you donate, I imagine they would know whether to eat more!

I donated blood not all that long after starting using MFP and never even thought about it at the time but fainted - I think there were a combination of reasons but had never had that issue before. So when I'm next allowed to go I will be making sure to have eaten a good number of my calories before going!

I'm no expert but personally would say make sure to have eaten a good size breakfast etc before going and judge as the day goes on what you need to do.

Yes, you should probably eat at maintenance or higher.

Your body will burn about 600 calories after you've donated a pint of blood to replenish your body. So your body needs all the energy it can get for that process. Make sure to hydrate, and get some iron!

Also, skip any exercise you might have planned, you don't want to pass out from over-exerting yourself.

I think we should specify this is NOT donating whole blood. This is plasma, they do return the red cells back to you. Just needed to clarify because I know it's vastly a different experience and wait time. With plasma donation you can donate twice per week.

Ah, I see. I think I read that for plasma, it's 450 calories, but don't quote me on that. I think it depends on how much plasma is actually taken.

But still, it may be better to keep those calories up.