Determination of tumor markers in serum. Pitfalls and good practice.

The determination of tumor markers may have consequences for the patients' treatment, which requires special attention to the analysis and to the expression of the results. In addition to the factors usually dealt with in the pre-analytical phase (identification, quality and storage of the sample) and in the analytical phase (interference, endogenous antibodies, hook effect), we must consider factors such as normal values (which depend heavily on the used techniques), threshold values defining other characteristics (sensitivity, specificity, positive and negative predictive value) and kinetics. Knowledge of the limitations of the tumor marker analysis, in particular tumor markers for non-cancerous diseases leading to possible increases (false positives), is also indispensable. All of this led to the definition of guidelines for good practice, including the design of quality control, rules for requesting, validation and interpretation of results, and the setting up of a serum library.