Comparing automated FXIII assays

Objective Plasma transglutaminase FXIII confers mechanical and biochemical stability to blood clots. Congenital or acquired FXIII deficiency occurs rarely but activity levels ≤ 30% may be associated with severe bleeding, therefore careful patient monitoring is recommended. There are several assays for the manual determination of FXIII, however there is still an unmet diagnostic need for a reliable high-throughput assay.

The aim of the study was to demonstrate the characteristics of automated FXIII assays which are suitable for use in routine laboratories.

Material and Methods Next to the well-established ammonia release-based assay, the turbidimetric based FXIII antigen assay was compared to the newly developed fluorogenic FXIII activity assay on Ceveron s100. The assay principle is based on the use of a highly sensitive fluorogenic substrate in combination with a thrombin reagent. FXIII is activated by thrombin. FXIIIa cleaves a dark quenching molecule from the side chain of a modified peptide incorporating glycine methyl ester. Subsequently, the fluorescence intensity of an N-terminal coupled dye increases and is detected by the automated coagulation analyser.

Results For method comparison 110 samples ranging from 0 to 150% factor XIII activity were measured with the respective assay on the companies corresponding analyser platform. In comparison to the chromogenic assay for FXIII activity a Passing and Bablok fit of y=-5.448 + 1.011x and correlation of ≥0.95 could be observed. The comparison to the turbidimetric antigen assay resulted in a Passing and Bablok fit of y=-1.184 + 1.124x and correlation of ≥0.95. When looking into individual samples some known discrepancies can be detected. In samples with high Fibrinogen levels (>5 g/L), the ammonia release assay did result in overestimation of FXIII by 15-25%. More importantly however, was the finding that functional deficiencies of factor FXIII were not detected by the antigen assay, which could be problematic as this assay is commonly used as sole FXIII assay in some laboratories.

Conclusion We have demonstrated in our study that automated FXIII assays work reliable and robust. However, the factor FXIII activity assays have to be seen advantageous as they also detect functional FXIII deficiencies due to inhibitors.

Publication History

Article published online:
18 June 2021