Flux variability of the exchange reactions can be used to detect metabolic signatures of simulated morbid SNPs and drug treated erythrocytes. (A) Exchange reactions are artificial reactions that allow the mathematical model to uptake and secrete metabolites into the extracellular space. Uptake of a metabolite into the erythrocyte is expressed as a negative value and secretion is expressed as a positive value. There are four major differences that can occur for an exchange reaction in two different states: i) the reaction is either active (non-zero minimum or maximum flux) or inactive (zero minimum and maximum flux), ii) the exchange becomes fixed in one direction (uptake or secretion only), iii) there is a magnitude change in exchange, iv) the reaction is unaffected and is the same for both states. (B) We detected 71% and 62% of the morbid SNPs and drugs associated with the erythrocyte. The distribution shows that most perturbed conditions have between one to ten differentially active exchange reactions.