A simple, quick one-step ELISA assay for the determination of complex plasma factor XIII (A2B2). 
A new highly sensitive sandwich ELISA assay was developed for the determination of plasma factor XIII (FXIII).  Plasma FXIII is a tetrameric complex of two types of subunits (A2B2).  A biotinylated monoclonal capture-antibody against the B-subunit and a peroxidase-labelled monoclonal tag-antibody against the A-subunit were added to the plasma dilution and the amount of the complex attached to streptavidin-coated microplate was quantitated by measuring peroxidase activity.  Only the tetrameric plasma FXIII reacted in the assay, non-complexed A or B subunits showed no reaction.  The assay is linear up-to 40 microg/L of FXIII in the assay mixture.  It is a quick one-step assay which can be performed within two hours.  At normal and low FXIII concentration within batch reproducibility was 2.0% and 3.3%, day to day variation was 5.5% and 8.7%, respectively.  Its high sensitivity allows reliable measurement at FXIII concentrations below 1% of normal average.  Plasma samples can be stored for the assay at -20 degrees C for at least one month.  Plasma levels of healthy individuals were normally distributed and no gender difference was observed.  A reference interval of 14-28 mg/L (67-133%) was established.