Probably not advisable! I have just completed W4R3 just 24hrs after giving blood. I have never had any ill-effects after giving blood so I thought I'd give it a go. Well, the final run was a major struggle... it was more like a fast shuffle than a run! But I pushed myself through it and made it somehow. Felt absolutely shattered afterwards (far more than W4R1 or W4R2) and I suspect I will be a bit sore tomorrow.
I think I'll give it at least 2 days after donation next time!