A computer-based method for determining total body albumin including determining a baseline of expected ratio of amount of albumin in an intravascular system to amount of albumin in an extravascular system, determining albumin concentration, calculating plasma volume based on detected counts of radiolabeled albumin injected into the living being, calculating an amount of intravascular albumin based on the calculated plasma volume and the determined albumin concentration, calculating an observed ratio of amount of albumin in the intravascular system to amount of albumin in the extravascular system at a first time after injecting the radiolabeled albumin, and calculating the total body albumin based on the calculated intravascular albumin, the calculated observed ratio of amount of albumin in the intravascular system to amount of albumin in the extravascular system, and the baseline of expected ratio of amount of albumin in the intravascular system to amount of albumin in the extravascular system.
