We have assessed the feasibility of using fixed-limit criteria based on medical 
relevance and biological variation for evaluating the analytical performance of 
the prostate-specific antigen (PSA) test. The estimated within-subject variation 
of serum PSA is on the order of 10-20% at clinical decision points. The 
calculated performance goals of 5-10% CV are attainable with current immunoassay 
technology and agree with precision goals based on clinical experience and the 
current clinical use of the test. However, new clinical applications of PSA may 
require a degree of analytical performance that current methods may not be able 
to provide. The PSA model demonstrates the need for biologically based 
fixed-limit criteria for all tumor-marker tests.