PB0153 - Analysis of positive protein S results among unselected consecutive patients referred for testing during one year period

Background: Laboratory evaluation of protein S (PS) represents an integral part of thrombophilia testing.

Aims: To analyze the results of laboratory evaluation of PS by free protein S antigen (fPS:Ag) and protein S activity (PS:Ac) assays.

Methods: FPS:Ag (immunological test with monoclonal antibody to unbound PS form) was measured (Innovance Free PS Ag assay, Siemens Healthineers, Germany) as first and main diagnostic step in 1382 consecutive patients referred for testing during one year period (2023). Additionally, for all patients with decreased, borderline or unclear fPS:Ag results, PS:Ac as functional clot based test was performed Protein S Ac, Siemens Healthineers, Germany). Statistical analysis was performed using descriptive statistics and Mann-Whitney rank sum test for testing significant differences between groups.

Results: The results of all PS positive patients among consecutive patients (n=1382) analyzed are presented in Table 1 and Figure 1. In total, there were 33 (2.4%) positive PS patients (with excluded all acquired states of PS positivity: pregnancy, anticoagulant/hormonal therapy, liver disease); 27 females and 6 males, showing significantly younger age of positive females than males (medians of 34 and 51 years, respectively, P= 0.014). There were no significant differences for both fPS:Ag and PS:Ac vaules among females and males (P=0.963 and P=0.375) as well as between fPS:Ag and PS:Ac levels neither for female nor male positives (P=0.979 and P=0.631). Among all 33 PS positives, 30 patients (0.91) had equally decreased values of fPS:Ag and PS:Ac, indicating quantitative type of PS deficiency, whereas 3 patients (0.09) had only slightly reduced fPS levels and significantly more reduced PS:Ac, corresponding to qualitative PS deficiency.

Conclusion(s): Our results confirmed that the current recommendations related to the fPS:Ag assay as the first and main diganostic step and PS:Ac assay as an additional test in case of decreased, borderline or unclear fPS:Ag results provide reliable and accurate diagnostics of PS deficiency.