Fibrinogen γ' levels in patients with intracerebral hemorrhage

Fibrinogen; a predictor of injury severity and mortality among patients with traumatic brain injury in Sub-Saharan Africa: A cross-sectional observational study

Studies show that fibrinogen concentrations <2 g/L in patients with traumatic brain injury (TBI) is associated with increased mortality. However, little is known regarding fibrinogen levels and TBI severity as well as mortality in sub-Saharan Africa despite shouldering a high burden of TBI. We therefore set out to determine whether fibrinogen levels are associated with TBI severity and outcome. To determine the sensitivity and specificity of fibrinogen levels and the association with severity and mortality among TBI patients at Mulago Hospital. We prospectively enrolled 213 patients with TBI aged between 13 and 60 years of age and presenting within 24 hours of injury. Patients with preexisting coagulopathy, concurrent use of anticoagulant or antiplatelet agents, preexisting hepatic insufficiency, diabetes mellitus and who were pregnant were excluded. Fibrinogen levels were determined using the Clauss fibrinogen assay. Logistic regression analyses were conducted to identify the association between fibrinogen level and 7-day outcomes. Majority of the patients were male (88.7%) and nearly half were aged 30 or less (48.8%). Fibrinogen levels <2 g/L were observed in 35.1% of the study participants. The average time spent in the study was 3.7 ± 2.4 days. The sensitivity and specificity using fibrinogen <2 g/L was 56.5% and 72.9% respectively. Fibrinogen levels predict TBI severity with an AUC = 0.656 (95% CI 0.58-0.73: P = .000) Fibrinogen levels <2 g/L (hypofibrinogenemia) were independently associated with severe TBI. (Adjusted odds ratio 2.87 CI, 1.34-6.14: P = .007). Levels above 4.5 g/L were also independently associated with injury severity (adjusted odds ratio 2.89, CI 1.12-7.48: P < .05) Fibrinogen levels more than 4.5 g/L were independently associated with mortality (OR 4.5, CI; 1.47-13.61, P < .05). The fibrinogen level is a useful tool in predicting severity including mortality of TBI. Fibrinogen levels may be used as an additional tool to screen TBI patients for injury severity especially among patients with Glasgow coma scale scores of <14.

Fibrinogen; a predictor of injury severity and mortality among patients with traumatic brain injury in Sub-Saharan Africa: a prospective study

Introduction

Fibrinogen levels drop quicker than any other factors in severe trauma such as Traumatic Brain Injury (TBI). Contemporaneous studies show that fibrinogen concentrations < 2 g/L are strongly related to mortality. However, little is known regarding fibrinogen levels and TBI severity as well as mortality in sub-Saharan Africa. We therefore set out to determine whether fibrinogen levels are associated with TBI severity and seven days outcomes.

Objectives

To determine the sensitivity and specificity of fibrinogen levels and the association with severity and mortality among TBI patients at Mulago Hospital.

Methods

We prospectively enrolled 213 patients with TBI aged between 13 and 60 years of age and presenting within 24hrs of injury. Patients with pre-existing coagulopathy, concurrent use of anticoagulant or antiplatelet agents, pre-existing hepatic insufficiency, diabetes mellitus and who were pregnant were excluded. Fibrinogen levels were determined using the Clauss fibrinogen assay.

Results

Majority of the patients were male (88.7%) and nearly half were aged 30 or less (48.8%). Fibrinogen levels less than 2g/L were observed in 74 (35.1%) of the patients while levels above 4.5 g/L were observed in 30(14.2%) of the patients. The average time spent in the study was 3.7 ± 2.4 days. The sensitivity and specificity using fibrinogen < 2g/L was 56.5% and 72.9% respectively. Fibrinogen levels predict TBI severity with an AUC = 0.656 (95% CI 0.58-0.73: p = 0.000) Fibrinogen levels < 2g/L (hypofibrinogenemia) were independently associated with severe TBI. (AOR 2.87 CI,1.34-6.14: p = 0.007). Levels above 4.5g/L were also independently associated with injury severity (AOR 2.89, CI 1.12-7.48: p < 0.05) Fibrinogen levels more than 4.5g/L were independently associated with mortality (OR 4.5, CI;1.47-13.61, p < 0.05).

Conclusions

The fibrinogen level is a useful tool in predicting severity including mortality of TBI in our settings. We recommend the routine use of fibrinogen levels in TBI patient evaluations as levels below 2g/L and levels above 4.5g/L are associated with severe injuries and mortality.

High fibrinogen γ' levels in patient plasma increase clot formation at arterial and venous shear

Fibrinogen γ' accounts for 3% to 40% of plasma fibrinogen. Earlier studies indicated that fibrinogen γ' forms altered fibrin clots under static conditions, whereas clinically, altered plasma γ' levels are associated with arterial and venous thrombosis. However, the effects of static vs flow conditions on the role of γ' throughout the pathophysiological range is unknown. This study explores the effects of γ' levels on clot formation and structure in static and flow conditions. Coagulation of plasma samples with low (n = 41; 3%), normal (n = 45; 10%), or high (n = 33; 30%) γ' levels were compared with that of purified fibrinogen mixtures with increasing ratios of γ' (3%, 10%, 30%). Clots were analyzed by confocal microscopy, permeation, turbidity, and lysis techniques. In a novel 2-step flow-perfusion model, fibrinogen-deficient plasma repleted with increasing ratios of γ' (3%, 10%, 30%) or plasmas with low (n = 5, 3%) or high (n = 5, 30%) γ' were flowed over preformed platelet aggregates at arterial (500 s-1) and venous (150 s-1) shear rates. Increasing γ' percentages within the pathophysiological range (3%-30%) did not result in any change in clot-formation rates; however, it led to significantly higher clot density, thinner fibers, and slower lysis in static conditions. Under flow at arterial shear, high γ' (30%) led to faster (+44.1%-75.3%) and increased (+104%-123%) fibrin deposition, with clots exhibiting a larger volume (+253%-655%) and height (+130%-146%). These trends were magnified at venous shear. Overall, our findings demonstrate the significant impact of pathophysiological fibrinogen γ' levels on clot structure and provide new flow-dependent mechanisms to explain how γ' increases thrombosis risk.

Natural anticoagulants: A missing link in mild to moderate bleeding tendencies

Introduction

There is a growing interest in natural anticoagulants as a cause of mild to moderate bleeding disorders (MBDs), particularly in patients with bleeding of unknown cause (BUC), which is defined as having a mild to moderate bleeding phenotype without a definite diagnosis despite exhaustive and repeated laboratory investigations. Recently, abnormalities in two natural anticoagulant pathways, thrombomodulin (TM), and tissue factor pathway inhibitor (TFPI), were identified in single patients or families as the underlying cause for a bleeding tendency.

Aim

The objective of this review is to discuss the current understanding of the role of natural anticoagulants in MBDs using available clinical and translational data.

Methods

A Cochrane Library and PubMed (MEDLINE) search focusing on selected natural anticoagulants and their role in MBDs was conducted.

Results

Data on the influence of natural anticoagulants including protein C, protein S, antithrombin, TM, and TFPI or factors with anticoagulant properties like fibrinogen gamma prime (γ’) on MBDs are scarce. Observations from sepsis treatment and from translational research highlight their importance as regulators of the haemostatic balance, especially via the activated protein C‐related pathway, and suggest a role in some MBDs.

Conclusion

Similar to the distinct genetic variants of natural anticoagulants linked to thrombosis, we hypothesize that novel variants may be associated with a bleeding tendency and could be identified using next generation sequencing.

Clinical and Radiographic Predictors of Intracerebral Hemorrhage Outcome

BACKGROUND

Intracerebral hemorrhage (ICH) represents 10-15% of all stroke cases in the US annually. Fewer than 40% of these patients ever reach long-term functional independence, and mortality rate is roughly 40% at 1 month. Due to the high morbidity and mortality rates after ICH, early detection of high-risk patients would be beneficial in directing the management course and goals of care. This review aims to discuss relevant clinical and radiographic characteristics that can serve as predictors of poor prognosis and examine their efficacy in predicting patient outcomes after ICH.

SUMMARY

A literature review was conducted on various clinical and radiographic factors. They were examined for their predictive value in relation to ICH outcome. Studies that focused on each of these factors were included, and their results analyzed for trends with regard to incidence, patient outcome, and mortality rate.

KEY MESSAGE

In this review, we examined clinical and radiographic characteristics that have been found to be significantly associated to a varying degree with poor outcome. Clinical and radiographic predictors of poor patient outcome are invaluable when it comes to identifying high-risk patients and triaging accordingly as well as guiding decision-making.

The effect of fibrin(ogen) on thrombin generation and decay

Defibrination causes a ~30% decrease of thrombin generation (TG) which can be restored by adding native fibrinogen in its original concentration (3 mg/ml). The fibrinogen variant γA/γ′, which binds thrombin with high affinity, is over four times more efficient in this respect than the more common γA/γA form. By using high tissue factor concentrations we accelerated prothrombin conversion so as to obtain a descending part of the TG curve that was governed by thrombin decay only. From that part we calculated the antithrombin (AT)- and α2-macroglobulin- dependent decay constants at a series of concentrations of native, γA/γA and γA/γ′ fibrinogen. We found that the increase of TG in the presence of fibrinogen is primarily due to a dose-dependent decrease of thrombin inactivation by α2-macroglobulin, where the γA/γ′ form is much more active than the γA/γA form. AT-dependent decay is somewhat decreased by γA/γ′ fibrinogen but hardly by the γA/γA form. We assume that binding of thrombin to fibrin(ogen) interferes with its binding to inhibitors. Attenuation of decay only in part explains the stimulating effect of fibrinogen on TG, as fibrinogen stimulates prothrombin conversion, regardless of the fibrinogen variant.

Note: Part of this work was presented at the ISTH meeting in 2013.

The fibrinogen γA/γ' isoform does not promote acute arterial thrombosis in mice

BACKGROUND

Elevated plasma fibrinogen is associated with arterial thrombosis in humans and promotes thrombosis in mice by increasing fibrin formation and thrombus fibrin content. Fibrinogen is composed of six polypeptide chains: (Aα, Bβ, and γ)2. Alternative splicing of the γ chain leads to a dominant form (γA/γA) and a minor species (γA/γ'). Epidemiological studies have detected elevated γA/γ' fibrinogen in patients with arterial thrombosis, suggesting that this isoform promotes thrombosis. However, in vitro data show that γA/γ' is anticoagulant due to its ability to sequester thrombin and suggest its expression is upregulated in response to inflammatory processes.

OBJECTIVE

To determine whether γA/γ' fibrinogen is prothrombotic in vivo.

METHODS

We separated γA/γA and γA/γ' fibrinogen from human plasma-purified fibrinogen and determined the effects on in vitro plasma clot formation and on in vivo thrombus formation and circulating thrombin-antithrombin complexes in mice.

RESULTS AND CONCLUSIONS

Both γA/γA and γA/γ' fibrinogen were cleaved by murine and human thrombin and were incorporated into murine and human clots. When γA/γA or γA/γ' was spiked into plasma, γA/γA increased the fibrin formation rate to a greater extent than γA/γ'. In mice, compared to controls, γA/γA infusion shortened the time to carotid artery occlusion, whereas γA/γ' infusion did not. Additionally, γA/γ' infusion led to lower levels of plasma thrombin-antithrombin complexes following arterial injury, whereas γA/γA infusion did not. These data suggest that γA/γ' binds thrombin in vivo and decreases prothrombotic activity. Together, these findings indicate that elevated levels of γA/γA fibrinogen promote arterial thrombosis in vivo, whereas γA/γ' does not.

Evidence that fibrinogen γ′ regulates plasma clot structure and lysis and relationship to cardiovascular risk factors in black Africans

This paper describes the effect of fibrinogen γ′ on clot structure in plasma (previously shown in purified systems). This paper also describes the respective roles of total fibrinogen, fibrinogen γ′ concentration, and ratio on clot structure and lysis rates.