The kidney allocation system aims to distribute kidneys from deceased donors in an equitable and potential-life optimising manner. This is a difficult task, not least because intrinsic biological differences, such as a person's ABO blood type, influence the allocation. This paper begins by presenting a curious and undocumented empirical fact: candidates on the kidney transplant waitlist with blood types implying they will more rapidly be offered a kidney display lower pre-transplant survival. The paper investigates whether this difference in pre-transplant survival is due to biological, behavioural, or spurious selection. To that end, we promote a two-in-one randomization design which allows us to credibly fit our empirical setting within a dynamic potential outcomes framework. Using this framework, drawing from economic theory, and noting problematic financial and legal market incentives, the paper systematically evaluates different explanations for pre-transplant survival patterns. Our analysis establishes a small set of behavioural explanations which directly inform debates about how to reduce the excessive discard of viable kidneys in the US transplant market.