Technical evaluation of factors interfering in the carcinoembryonic antigen assay.

Storage of serum or plasma at room temperature (RT) or 4 degrees C for eight days did not alter the level of carcinoembryonic antigen (CEA). However, storage of whole blood at RT for 8 days resulted in false elevated CEA levels compared to controls. Heating of serum or plasma at 56 degrees C for 30 min or freezing and thawing for fifteen times did not change the CEA levels in these specimens. Comparison of CEA levels in the serum and plasma of the same specimens showed significantly higher levels of CEA in plasma than serum specimens. Collection of blood in tubes with different anticoagulants showed significantly false elevated levels of CEA only when blood was collected in heparinized tubes. These data indicate the importance of knowing the factors interfering in the CEA assay when interpreting its results.