Abstract
The time interval between collection of specimens from an individual patient is usually determined empirically. For analytes whose values decline according to first-order kinetics--for example, enzyme activities in serum after an acute myocardial infarction, tumor markers in serum after excision of the tumor, and drugs in serum after an overdose--the minimum time between collections (delta T) depends on the elimination half-life (t) and the analytical precision (CVA), according to the equation: delta T = (1/log2) X t X log (2.33 CVA/100 + 1). Nomograms showing this relationship graphically have been generated.