Hypercoagulability in splenectomized thalassemic patients detected by whole-blood thromboelastometry, but not by thrombin generation in platelet-poor plasma.

Background: The mechanisms responsible for the increased thrombotic risk associated with thalassemia are still unclear. They might be related to the effects of red blood cell or endothelial cell derangements, increased numbers of platelets as well as abnormal plasma coagulation.

Design And Methods: To evaluate the relative role played by cells and plasma we investigated 169 patients with thalassemia by means of thromboelastometry and thrombin generation tests.

The history of phenotypic testing in thrombosis and hemostasis.

This article takes the reader through a journey of the history of the phenotypic tests for hemostasis and thrombosis starting from the most simple (which were based on the visual inspection and recording of the time needed for native whole blood to clot) to the more complex ones based on the addition to plasma of exogenous substances, use of sophisticated coagulometers or synthetic substrates, and use of computer software to record coagulation times or visualize coagulation tracings and thrombin generation curves. One can see how the simple tests evolved over the years and how such old and time-honored tests as thrombin generation and thromboelastography, devised more than 50 years ago and neglected for many years, are now gaining momentum thanks to the progress made by the technology combined with a better understanding of the coagulation mechanisms. This progress notwithstanding, it should be realized that current tests are still somewhat far from being adequate to investigate hemostasis and thrombosis.

Laboratory testing for lupus anticoagulants: diagnostic criteria and use of screening, mixing, and confirmatory studies.

The presence of lupus anticoagulants (LA) in plasma is a strong risk factor for thromboembolism and fetal loss. Because of this, demand for testing for LA is increasing, but the performance of clinical laboratories in terms of its detection is still a matter of concern. This is due in part to the lack of specific tests but also to the lack of standardization and application of the diagnostic criteria.

Second international collaborative study evaluating performance characteristics of methods measuring the von Willebrand factor cleaving protease (ADAMTS-13).

Background: Over the last 4 years ADAMTS-13 measurement underwent dramatic progress with newer and simpler methods.

Aims: Blind evaluation of newer methods for their performance characteristics.

Design: The literature was searched for new methods and the authors invited to join the evaluation.

High thrombin generation measured in the presence of thrombomodulin is associated with an increased risk of recurrent venous thromboembolism.

Background: The assessment of the risk of recurrent venous thromboembolism (VTE) is important to determine the optimal duration of secondary prophylaxis. The risk can be estimated by measuring individual parameters reflecting hypercoagulability. Because of the large numbers of such putative parameters, the assessment in individual patients is complex.

Normal thrombin generation in neonates in spite of prolonged conventional coagulation tests.

Conventional coagulation tests might be inadequate to explore mechanisms regulating thrombin generation in neonates, because they do not allow full activation of the reduced levels of protein C. Therefore, they do not reflect the action of pro- and anti-coagulants as does the endogenous thrombin potential assessed in the presence of thrombomodulin. Endogenous thrombin potential measured without thrombomodulin was greater than the lower-limit of the adult reference interval in 30% of 109 full-term and 49% of 55 pre-term neonates, a finding consistent with the reduced levels of procoagulants in this setting.

The international normalized ratio to prioritize patients for liver transplantation: problems and possible solutions.

The prothrombin time (PT) test once designed by Dr Quick to investigate patients with obstructive jaundice was later adapted and standardized by means of the international normalized ratio (INR) to monitor patients on treatment with vitamin K antagonists (VKA). After more than 70 years from its introduction it is now time to think about its standardization for those very patients for whom it was intended at the beginning of its history. Two studies carried out independently and published recently in the same issue of a specialized journal do exploit the very same idea on how to accomplish this standardization.

Interference of factor V Leiden on protein S activity: evaluation of a new prothrombin time-based assay.

Protein S activity in plasma from factor V Leiden (FVL)-positive patients may be lower than expected. We investigated a new commercially available method for protein S for such interference. Protein S activity was measured for plasmas from 50 individuals with FVL and their results were compared with those obtained for plasmas from 47 sex-matched and age-matched individuals without FVL.

The endogenous thrombin potential and the risk of venous thromboembolism.

Background: The risk of venous thromboembolism (VTE) is increased by an excess of procoagulant or by a defect of anticoagulant proteins, with circumstantial risk factors playing a significant contribution. These conditions are directly linked to or are compatible with increased thrombin generation. Assuming that the more thrombin is generated the higher is the risk of VTE, an overall coagulation test monitoring ex vivo thrombin generation and reflecting the interaction of pro- and anticoagulant proteins would be useful to determine the risk of VTE.

Issues concerning the laboratory investigation of inherited thrombophilia.

Inherited thrombophilia, defined as an increased familial tendency to develop thrombosis, may be due to congenital deficiencies or abnormalities of antithrombin, protein C or protein S; to the presence of a point mutation in the factor V gene (G1691A, factor V Leiden) leading to a poor anticoagulant response to activated protein C; or to the presence of a mutation in the prothrombin gene (G20210A) leading to increased plasma levels of prothrombin. The laboratory investigation of inherited thrombophilia should be limited to patients with a history of venous thromboembolism and, if positive, to their family members even though they are still asymptomatic. There is no indication for indiscriminate screening of the general population or screening of asymptomatic women before prescribing oral contraceptives.

Usefulness of lyophilized calibration plasmas for International Normalized Ratio determination with the bovine combined thromboplastin (Thrombotest): results of a collaborative study.

The logical solution to account for the influence of coagulometers on the International Sensitivity Index (ISI) is local calibration with freeze-dried plasmas. However, because of their unpredictable behavior these plasmas must be validated before large-scale implementation. We report on a collaborative exercise designed to evaluate the suitability of a set of such plasmas used with Thrombotest in combination with a coagulometer provided by the manufacturer to be used with that reagent.

Evidence of normal thrombin generation in cirrhosis despite abnormal conventional coagulation tests.

The role played by coagulation defects in the occurrence of bleeding in cirrhosis is still unclear. This is partly due to the lack of tests that truly reflect the balance of procoagulant and anticoagulant factors in vivo. Conventional coagulation tests such as prothrombin time and activated partial thromboplastin time are inadequate to explore the physiological mechanism regulating thrombin, because they do not allow full activation of the main anticoagulant factor, protein C, whose levels are considerably reduced in cirrhosis.

A review of the clinical and diagnostic utility of laboratory tests for the detection of congenital thrombophilia.

Laboratory tests to detect congenital thrombophilia are frequently requested by clinicians. This review attempts to define (1) whether and to what extent laboratory testing may help clinicians make decisions on patient management, (2) the types of conditions to be investigated, and (3) the types of testing to be performed for each condition.

Measurement of von Willebrand factor cleaving protease (ADAMTS-13): results of an international collaborative study involving 11 methods testing the same set of coded plasmas.

Background: ADAMTS-13 is a von Willebrand factor (VFW)-cleaving protease. Its congenital or acquired deficiency is associated with thrombotic thrombocytopenic purpura (TTP) and more rarely with the hemolytic uremic syndrome. We report on a survey evaluating 11 methods for ADAMTS-13 measurement performed in different labs.

A shortened activated partial thromboplastin time is associated with the risk of venous thromboembolism.

Hypercoagulability due to high coagulation factors XI, VIII, IX, II, and fibrinogen is recognized as a risk factor of venous thromboembolism (VTE). These factors are cumulatively explored by the activated partial thromboplastin time (APTT). To test the hypothesis that a short APTT increases the risk of VTE, a case-control study was carried out in 605 patients referred for thrombophilia testing after documented VTE and in 1290 controls.

Prothrombin time international normalized ratio monitoring by self-testing.

Purpose Of Review: The increasing numbers of patients on oral anticoagulants may challenge the traditional organization of patient monitoring. The availability of portable coagulometers capable of measuring prothrombin time (PT) international normalized ratio (INR) in a drop of capillary blood facilitates decentralization of monitoring by self-testing. This article reviews the literature on use of portable coagulometers.

Oral anticoagulant monitoring by laboratory or near-patient testing: what a clinician should be aware of.

Prothrombin time (PT) is the primary laboratory test for monitoring oral anticoagulant treatment but is influenced by preanalytical conditions and analytical variables, that is, thromboplastin reagents and instrumentation. Standardization and normalization of test results is mandatory. PT results should be transformed to International Normalized Ratio (INR) by calibration of the reagent/instrument system with International Reference standards according to World Health Organization guidelines.

Quality assurance program for whole blood prothrombin time-international normalized ratio point-of-care monitors used for patient self-testing to control oral anticoagulation.

Whole blood coagulation monitors are increasingly used for patient self-testing to control oral anticoagulation, but there are no comprehensive quality assurance (QA) programs to check their performance. We report on the experience with one of such programs applied in a field study where patients on prothrombin time (PT)-international normalized ratio (INR) self-testing were asked to bring their monitors to the anticoagulation clinic for checking. PT-INR testing was performed three times over 3 months with 14 patient's monitors and test strips on three recalcified QA plasmas by an experienced laboratory operator.

Standardization of the endogenous thrombin potential measurement: how to minimize the effect of residual platelets in stored plasma.

Platelet contamination in stored plasma may affect coagulation assays, including the endogenous thrombin potential (ETP), which has been proposed for the investigation of hyper- and hypo-coagulability. The current recommendation of filtering plasma before freezing cannot be always met. This study provides evidence that filtering frozen plasma after thawing, prior to testing, may help to eliminate the unwanted effect of residual platelets on the ETP.

Measurement of warfarin in plasma by high performance liquid chromatography (HPLC) and its correlation with the international normalized ratio.

The measurement of plasma warfarin is required to investigate non-compliance, resistance to anticoagulation, drug metabolism and pharmacokinetic. Methods so far described are based on extraction of warfarin from plasma followed by reversed-phase HPLC. Extraction is the crucial step and may be performed in liquid- or solid-phase.

Lupus anticoagulant (LA) testing: performance of clinical laboratories assessed by a national survey using lyophilized affinity-purified immunoglobulin with LA activity.

Background: Lupus anticoagulant (LA) screens are frequently ordered in the workup of thrombophilic patients or women with fetal loss. The sensitivity and specificity of LA detection vary depending on the choice of tests, cutoff values, and results interpretation. This variation is detrimental to patient management because persistent LA positivity in patients with a history of thrombosis is a requisite for long-term anticoagulation therapy.

Laboratory diagnosis of thrombophilic states: where do we stand?

Until recently the laboratory diagnosis of thrombophilia consisted on investigation of the plasmatic anticoagulant pathways and the search for dysfibrinogenemia and antiphospholipid antibodies/lupus anticoagulants. More recently, the laboratory investigation has been expanded by including activated protein C (APC) resistance, due or not to the presence of the factor V Leiden mutation; hyperprothrombinemia, due to the presence of the prothrombin mutation G20210A and hyperhomocysteinemia, due to impairment of the relevant metabolic pathway because of enzymatic and/or vitamin deficiency. Testing for thrombophilia may be useful for many reasons.

Levels of coagulation factors and venous thromboembolism.

Background And Objectives: Altered levels of coagulation factors have been included among the abnormalities that may increase the risk of venous thromboembolism (VTE) in otherwise healthy subjects.

Information Sources: According to the studies that have been carried to test this hypothesis only elevated levels of factor VIII and fibrinogen emerged as independent risk factors for VTE.

State Of The Art And Perspectives: Although some data indicate that elevated levels of factor XI or IX are also determinants for VTE, this awaits confirmation.