PRELOG: precedence logic inference software for blood donor deferral.

Blood collection facilities have recently witnessed a substantial increase in the complexity of tests used to detect infectious disease in donor populations, and there is a stringent regulatory effort by the Food and Drug Administration (FDA) to validate the software for managing this information. PRELOG is precedence-based inference software used to determine a donor's suitability for continued donations and whether the donation can be released for transfusion. PRELOG accepts ternary input for test results (positive, negative, or undetermined), and solves the logic rules sequentially, so that the rulebase can be validated in a concise and consistent manner.