#The most likely possibility is that Bruce has O+ or A+ blood. In my not-expert opinion.

[thecruellestmonth]

statistically improbable number of unrelated Batdudes with O- blood

People with O- blood make up 2.68% of the world population, 6.6% of the USA population, and 8% of the UK population.

People with O- blood can only receive O- whole blood transfusions.

Jason is confirmed to have O- blood. // Detective Comics #1032

Bruce is implied (but not confirmed) to have O- blood. // Batman (2016) Annual #3

Dick can donate blood to Bruce. // Batman/Nightwing: Bloodborne

Alfred has the same blood type as Bruce. // Batman Annual #13

The Joker can donate blood to Alfred. // The Brave and the Bold (1955) #141