PB0794 - Fibrinogen protects against histone-induced thrombocytopaenia

Background: Thrombocytopaenia, frequently observed in critical illness and predisposes to poor outcomes, is induced by high cell-free histone (CFH) levels (>30μg/mL). Fibrinogen (FBG), a coagulation factor, electrostatically binds and precipitates CFH.

Aims: We investigated (1) if this interaction protects against CFH-induced platelet activation, and (2) does CFH:FBG ratio have predictive utility for the development of clinically significant thrombocytopaenia in critical illness.

Methods: Isolated washed platelets were incubated for 15 minutes with CFH (50µg/mL), with or without FBG pre-incubation (4g/L). Platelet activation was assessed by fold-change in CD62P-PE mean fluorescent intensity by flow cytometry. Platelet aggregation was monitored turbidometrically (405nM).
CFH:FBG predictive utility was assessed through retrospective study of 278 patients admitted to the intensive care unit (ICU) at the Royal Liverpool University Hospital. Serial daily measurements across study duration (Days 1-4) included whole-blood cell counts, coagulation parameters, and CFH levels (quantified by Western blot).

Results: Pre-incubation of CFH with FBG significantly reduces CFH-induced platelet activation (CFH alone; CD62P-PE=3.49±0.33 vs CFH+FBG; CD62P-PE=1.12±0.06, p< 0.001), which was comparable to untreated controls (UT; CD62P-PE=0.88 ± 0.08). Similar results were obtained using platelet aggregometry (CFH alone; 23.2±1.7% vs CFH+FBG; 11.1±5.7%, p< 0.05).
To determine the clinical threshold of CFH:FBG, we performed receiver operating curve analysis. CFH:FBG on ICU admission was used to predict the development of moderate-to-severe thrombocytopaenia (PLT < 100x109/L) during the study duration (AUC=0.72). Sensitivity-specificity analysis and Youden’s index calculation demonstrated an optimal CFH:FBG cut-off of 6.
29.5% patients (82/278) had CFH:FBG≥6 and 70.5% (196/278) a CFH:FBG < 6. 59.8% (49/82) of those with CFH:FBG≥6 developed moderate-to-severe thrombocytopaenia, compared to 22.2% (43/196) of those with CFH:FBG < 6 (p < 0.001). Nadir platelet count in the CFH:FBG≥6 cohort was significantly lower compared to CFH:FBG < 6 [median=140 (Q1-Q3=80-264)x109/L vs median=237 (Q1-Q3=151-331)x109/L, p< 0.001].

Conclusion(s): FBG protects against CFH-induced thrombocytopaenia. CFH:FBG≥6 may help predict development of clinically significant thrombocytopaenia.