Nicholas has type O blood type which makes things slightly complicated. People with type O can donated blood or organs pretty much to anyone, but receiving one is a different story. He can only accept an organ from someone with the same blood type.

Having the same blood type does not automatically mean you can be a donor though. There are many tests performed to make sure you are compatible match as well as health risk assessments and financial burden.

Although the procedure to donate is covered by the recipients insurance, work compensation is not. These superheroes, along with their families, make enormous sacrifices. They risk everything to save another human being.