Antithrombotic and antifibrinolytic effects of antithrombin III replacement in liver cirrhosis

The International Normalized Ratio overestimates coagulopathy in stable trauma and surgical patients

BACKGROUND

The international normalized ratio (INR) was developed to assess adequacy of Coumadin dosing. Its use has been generalized to guide fresh frozen plasma (FFP) therapy in stable patients. Thrombelastography (TEG) is a whole-blood assay measuring the viscoelastic properties of the clot in near real time. This study hypothesized that INR does not reflect coagulopathy and should not be used to guide FFP therapy in stable trauma and surgical patients.

METHODS

Prospective observational data were collected from stable trauma and surgical patients (n = 106) who received FFP transfusions. Pretransfusion and posttransfusion blood samples were obtained to assess complete blood count, standard coagulation parameters (INR, partial thromboplastin time, fibrinogen and D-dimer), soluble clotting factors (II, V, VII, VIII, IX, X, XI, XII, proteins C and S) and TEG. Data were analyzed using a Mann-Whitney U-test. Significance was defined as p < 0.05.

RESULTS

A total of 262 U of FFP were transfused, with 78% of 106 patients receiving two or more units. Despite a reduction in INR, median TEG values remained within normal limits, while clotting factor levels retained adequate function to produce normal clotting before and following FFP transfusion.

CONCLUSION

The use of FFP in this population did not affect coagulation status in a clinically relevant manner based on TEG values and coagulation factor function. INR is not a predictor of coagulopathy and should not be used to guide coagulation factor replacement in stable trauma and surgical patients.

LEVEL OF EVIDENCE

Diagnostic study, level III.

Review article: the prothrombin time test as a measure of bleeding risk and prognosis in liver disease

BACKGROUND

Prothrombin time (PT)-derived international normalized ratio (INR) is used to assess bleeding risk and prognosis in cirrhosis, and to guide management of associated coagulation disturbances. Recent studies cast doubt on the validity of the assumptions that form the basis for these applications.

AIMS

To review and critique the use of the PT-INR in cirrhosis.

METHODS

Search of the literature.

RESULTS

In cirrhosis, there is a decrease in both pro- and anti-coagulants. The PT-INR measures only the activity of procoagulants and fails to capture changes in anticoagulants. It is therefore not surprising that the PT does not predict the bleeding risk. The PT-INR provides a robust measure of liver function but recent data showed INR inter-laboratory variability in this setting. This is not surprising as the INR was validated to normalize results for patients on vitamin-K antagonists, not for cirrhosis. This limitation was not appreciated, but the INR is used to construct the model for end-stage liver disease score to prioritize patients for liver transplantation. Reports showed that model for end-stage liver disease is modified by the thromboplastin used for testing.

CONCLUSIONS

Alternate tests to predict bleeding risk should be developed. The potential for misuse of the PT-INR should drive the development of alternate algorithms for organ allocation.

Reduction of D-dimer levels after therapeutic administration of antithrombin in acquired antithrombin deficiency of severe sepsis

Introduction

In acute disseminated intravascular coagulation, the effect of antithrombin (AT) administration on elevated levels of D-dimer is not well established. In the present study, we report on changes in circulating levels of D-dimer in response to administration of AT in a series of patients with acquired AT deficiency due to severe sepsis.

Methods

Eight consecutive critically ill medical patients presenting with acute disseminated intravascular coagulation associated with severe sepsis/septic shock received a single bolus infusion of AT over 30 minutes, aiming to achieve physiological AT levels. Haemostatic parameters including D-dimer were assessed prior to, 6 and 24 h after AT administration. An average of 42 ± 9 U/kg body weight was infused.

Results

Following AT substitution, elevated levels of D-dimer fell whereas AT levels rose.

Conclusion

These observations support the notion that AT can favourably affect fibrin degradation accompanying disseminated intravascular coagulation of severe sepsis.

[The paradox of disseminated intravascular coagulation]

Disseminated intravascular coagulation (DIC) is an abnormal extension of a coagulation process normally limited in time and space. DIC results from the release of free thrombin in circulating blood, as thrombin synthesis and inactivation mechanisms non longer function properly. In addition to microthrombosis, acute DIC may lead to haemorrhage related to activation of the coagulation process. According to the disease aetiology, emergency treatment may become a top priority, in case of haemorrhage, shortage of platelets and coagulation factors related to increased use of these blood components requires replacement treatment with infusion of platelets and fresh frozen plasma. As treatment of the procoagulation process, heparin should not be recommanded in acute DIC with haemorrhage. Based on rational theoretical data, current evaluation of antithrombin therapy is in progress.