Dilute prothrombin time-based lupus ratio test. Integrated LA testing with recombinant tissue thromboplastin

Area of Science:

• Hematology
• Clinical Chemistry
• Immunology

Background:

• The lupus ratio (LR) test quantifies lupus anticoagulant (LA) activity by comparing clotting times at varying phospholipid concentrations.
• Existing LR tests, such as those based on dilute activated partial thromboplastin time (dAPTT) and dilute Russell viper venom time (dRVVT), are established diagnostic tools.

Purpose of the Study:

• To develop and validate an automated LR test utilizing the dilute prothrombin time (dPT) assay.
• To assess the agreement and correlation of the novel dPT-based LR test with established dAPTT- and dRVVT-based LR tests.

Main Methods:

• An automated LR test was developed using recombinant thromboplastin and the dPT principle.
• Plasma samples from 92 patients with defined LA status were analyzed.
• The dPT-LR test results were compared with dAPTT-LR and dRVVT-LR tests using kappa statistics and correlation coefficients.

Main Results:

• The dPT-LR test demonstrated fair agreement with dAPTT-LR (kappa=.60) and good agreement with dRVVT-LR (kappa=.78) in classifying LA-negative and -positive plasmas.
• Correlation between dPT-LR and dRVVT-LR was moderate (r(s)=.51), while correlation with dAPTT-LR was nonsignificant (r(s)=.23).
• The dAPTT-LR test showed the highest sensitivity in detecting LA using plasma dilutions.

Conclusions:

• The dPT-based LR test is a valid and reproducible assay for LA detection.
• The findings support the concept of antibody heterogeneity in LA-positive plasmas.
• Performing multiple LR tests is recommended for comprehensive LA diagnosis due to moderate correlations between different assay types.