Clauss assay and fibrinogen protein estimated by capillary zone electrophoresis

The clottability and the amount of total protein in fibrinogen provide information about qualitative or quantitative alterations. We aimed to evaluate whether capillary zone electrophoresis (CZE) Capillarys II analyzer with the protein 6 buffer is able to estimate the amount of fibrinogen antigen.

Citrated plasmas were assayed for clottable fibrinogen, and any relationship with the β(2)-globulin fraction (percentage of the area under the curve) was evaluated. The integration method used was "tangent skimming" in order to reduce the overestimation due to high protein background. Linearity was optimized according to the ICH Q2R1 recommendations and evaluated using polynomial regression. The precision was computed in accordance with the Clinical and Laboratory Standards Institute EP5-A2 protocol. In patients, clottable fibrinogen (Clauss method) was compared to its protein CZE amount by Passing and Bablok regression and the Bland-Altman plot.

The correlation was linear y=0.0744+0.8991x (R(2)=0.9707) within the range of 2.26-17.26 μmol/L. The repeatability and the within-device precision were <15% for three levels of percentage of the β(2)-globulin fraction (1.61%, 3.51%, and 9.24%). In patients, clottable fibrinogen and its protein amount were similar (-0.1779+0.9654x). The ratio activity/protein was 1.08 ± 0.32 (mean ± 2 SD).

CZE with the Capillarys II and the buffer protein 6 is an easy method. It is a good candidate for estimation of the concentration of fibrinogen antigen, which may have diagnostic utility for the screening of quantitative or qualitative fibrinogen abnormalities.