Detection of shortened activated partial thromboplastin times: An evaluation of different commercial reagents

Are shortened aPTT values always to be attributed only to preanalytical problems?

OBJECTIVES

It has been recognized that shortened activated partial thromboplastin time (aPTT) may be caused by various preanalytical conditions. As coagulation Factor VIII is included in the in vitro intrinsic coagulation cascade measured by aPTT, we hypothesized that the shortened aPTT could be a result of elevated FVIII activity. We aimed to inspect the connection of elevated FVIII with shortened aPTT, and the possible effect inflammation has on routine laboratory parameters.

METHODS

40 patients from various hospital departments with aPTT measurement below the lower limit of the reference interval (<23.0 s) were included in the study. To compare the obtained results with aPTT measurements in the non-inflammatory state, samples from 25 volunteers (laboratory personnel) were collected. White blood cell count, C-reactive protein, aPTT, and FVIII values were measured in the control group.

RESULTS

Only two samples among 40 patients with shortened aPTT (5 %) were clotted. Out of the remaining 38, 26 had FVIII activity above 150 % (upper limit of a reference interval), median value of 194 % (IQR: 143-243 %). Seven samples in the control group had shortened aPTT results (36 %). However, all coagulation samples were clot and hemolysis-free. Multiple regression identified only FVIII activity as an independent variable in predicting aPTT values (p=0.001).

CONCLUSIONS

Our results support the thesis that shortened aPTT is rarely a consequence of preanalytical problems. Elevated FVIII activity causes shortened aPTT, not only in the inflammatory state but also in individuals with concentration of inflammatory markers within reference intervals.

Viewpoint: Lupus anticoagulant detection and interpretation in antiphospholipid syndrome

Lupus anticoagulant (LA) is a well-established risk factor for the clinical manifestations of antiphospholipid syndrome (APS). Accurate LA detection is an essential prerequisite for optimal diagnosis and management of patients with APS or aPL carriers. Variability remains a challenge in LA testing, with reliable detection influenced by multiple factors, including pre-analytical conditions, anticoagulation treatment, choice of tests and procedures performed, as well as interpretation of results, that can lead to false-positives or negatives. A standardised approach to LA testing, following current guidance, based on published data and international consensus, and with attention to detail, is required to underpin accurate detection of LA. Future work should focus on better characterisation of the nature of LA, which may ultimately lead to improved diagnosis and management of patients with APS and aPL carriers. This article reviews current practice and challenges, providing an overview on detection of LA.

Survey on antiphospholipid syndrome diagnosis and antithrombotic treatment in patients with ischemic stroke, other brain ischemic injury, or arterial thromboembolism in other sites: communication from ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

BACKGROUND

The optimal strategy for diagnosis and antithrombotic treatment of patients with antiphospholipid syndrome (APS)-associated acute ischemic stroke (AIS), transient ischemic attack (TIA), or other brain ischemic injury is poorly defined.

OBJECTIVES

The survey goal was to capture variations in diagnosis and antithrombotic treatment of APS-associated ischemic stroke and related disorders to inform guidance and clinical trials to define optimal management.

METHODS

Professional colleagues, including key opinion leaders, were invited to complete a REDCap survey questionnaire initiated by the International Society on Thrombosis and Haemostasis Scientific and Standardisation Committee Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies. The survey data were tallied using simple descriptive statistics.

RESULTS

There was generally good agreement on several aspects, including which patients to test for antiphospholipid antibodies (aPL), use of a lifelong vitamin K antagonist for AIS or recurrent TIA, and formal cognitive assessment for suspected cognitive impairment. There was less agreement on other aspects, including aPL testing for brain ischemic injury other than AIS/TIA or if an alternative cause for AIS or TIA exists; choice of aPL tests, their timing, and age cutoff; the aPL phenotype to trigger antithrombotic treatment; management for patent foramen ovale; antithrombotic treatment for first TIA or white matter hyperintensities; head magnetic resonance imaging specifications; and low-molecular-weight heparin dosing/anti-Xa monitoring in pregnancy. The survey highlighted that approximately 25% practice at dedicated APS clinics and <50% have a multidisciplinary team structure for patients with APS.

CONCLUSION

Much of the variation in practice reflects the lack of evidence-based recommendations. The survey results should inform the development of a more uniform multidisciplinary consensus approach to diagnosis and antithrombotic treatment.

Antiphospholipid Syndrome: State of the Art of Clinical Management

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder clinically characterized by recurrent arterial and venous thrombosis and/or pregnancy morbidity in the presence of antiphospholipid antibodies. Currently, treatment is mainly focused on anticoagulation, but therapies targeting mechanisms involved in APS autoimmune pathogenesis could play an important role in specific settings. An evidence-based therapeutic approach is limited by the broad clinical spectrum of the syndrome and the nature of a "rare disease" that makes it difficult to carry out well-designed prospective studies. Vitamin K antagonists (AVK), notably warfarin, are the standard treatment for preventing recurrent venous thrombosis and perhaps also arterial thrombosis. Direct oral anticoagulants (DOACs) are not recommended at least in patients with triple positivity APS. Treatment options for the prevention of pregnancy complications in obstetric APS, as combined use of aspirin and heparin, low-dose prednisolone, hydroxychloroquine, intravenous immunoglobulin (IVIG), may improve pregnancy outcome. The catastrophic antiphospholipid syndrome (CAPS) is the most severe form of APS with acute multiple organ involvement and small vessel thrombosis. Glucocorticoids, heparin, plasma exchange or IVIG, rituximab, or eculizumab must be added to concurrent treatment of precipitating factors (e.g. infections) as rescue therapies. Finally, it has been observed that SARS COV2 infection may produce vascular complications mimicking the clinical and pathophysiological features of APS and particularly of CAPS. From this point of view, attention has been focused on the "protective" role of anticoagulant therapy in preventing thrombotic complication when these clinical conditions coexist.

Testing for Lupus Anticoagulants

Lupus anticoagulant (LA) is one of the three criteria antiphospholipid antibodies (aPLs) employed in classification, and by default diagnosis, of antiphospholipid syndrome (APS). Detection of LA is not via calibrated assays but is based on functional behavior of the antibodies in a medley of coagulation assays. A prolonged clotting time in a screening test is followed by demonstration of phospholipid dependence and inhibitory properties in confirmatory and mixing tests, respectively, which are modifications of the parent screening test. Complications arise because no single screening test is sensitive to every LA, and no test is specific for LA, because they are prone to interference by other causes of elevated clotting times. Several screening tests are available but the pairing of dilute Russell's viper venom time (dRVVT) with LA-sensitive activated partial thromboplastin time (aPTT) is widely used and recommended because it is proven to have good detection rates. Nonetheless, judicious use of other assays can improve diagnostic performance, such as dilute prothrombin time to find LA unreactive with dRVVT and aPTT, and the recently validated Taipan snake venom time with ecarin time confirmatory test that are unaffected by vitamin K antagonist and direct factor Xa inhibitor anticoagulation. Expert body guidelines and their updates have improved harmonization of laboratory practices, although some issues continue to attract debate, such as the place of mixing tests in the medley hierarchy, and areas of data manipulation such as assay cut-offs and ratio generation. This article reviews current practices and challenges in the laboratory detection of LA.

APTT therapeutic range for monitoring unfractionated heparin therapy. Significant impact of the anti-Xa reagent used for correlation

INTRODUCTION

Unfractionated heparin (UFH) therapy is monitored by using the anti-activated factor X (anti-Xa) activity, or the activated partial thromboplastin time (APTT), which remains the most widely used assay. One of the main advantages of anti-Xa relies on its hypothesized standardization, with a unique therapeutic range (0.30-0.70 IU/ml) for all reagents, whereas APTT is influenced by numerous preanalytical and analytical parameters not related to the anticoagulant activity of UFH.

METHODS

The aim of this study was to compare the anti-Xa-correlated APTT therapeutic ranges calculated using different combinations of APTT (n = 4) and anti-Xa reagents (n = 4) in frozen citrated plasmas from 87 inpatients on UFH.

RESULTS

The median APTT ratio ranged from 2.19 for the less sensitive to 3.23 for the most sensitive reagent, whereas the median anti-Xa activity was between 0.37 IU/ml and 0.57 IU/ml. The APTT therapeutic ranges calculated to correlate with anti-Xa activities between 0.30 and 0.70 IU/ml were found to be highly different from one combination of APTT reagent and analyzer to another. The same applied to the therapeutic range of a single APTT reagent calculated using different anti-Xa assays performed on the same analyzer, leading to a lack of agreement as to whether a sample was classified as subtherapeutic, therapeutic or supratherapeutic in 8.0% to 23.0% of the patients, with kappa coefficients between 0.908 and 0.753.

CONCLUSIONS

These results suggest that the APTT therapeutic range calculated to correlate with anti-Xa activities between 0.30 and 0.70 IU/ml is influenced not only by the APTT reagent, but also by the anti-Xa reagent used for calculation.

The Predictive Value of the aCL and Anti-β2GPI at the Time of Acute Deep Vein Thrombosis-A Two-Year Prospective Study

Antiphospholipid syndrome (APS) is an important cause of deep vein thrombosis (DVT). According to current APS classification criteria, APS cannot be confirmed until 24 weeks after DVT. This time frame results in frequent discontinuation of anticoagulant treatment before APS is diagnosed. Therefore, the aim of our study was to evaluate the potential predictive value of anticardiolipin (aCL) and anti-β2glycoprotein I (anti-β2GPI) before discontinuation of anticoagulation therapy. Patients with newly diagnosed DVT were included into a 24-month prospective study. All patients received anticoagulant therapy. aCL and anti-β2GPI were determined at inclusion and every four weeks for the first 24 weeks and then one and two years after inclusion. APS was confirmed in 24/221 (10.9%) patients. At the time of acute DVT 20/24 (83.3%), APS patients had positive aCL and/or anti-β2GPI. Two patients had low aCL levels and two were negative at the time of acute DVT but later met APS criteria due to lupus anticoagulant (LA). Our data indicate that negative aCL and/or anti-β2GPI at the time of acute DVT make further aPL testing unnecessary; however, LA should be determined after discontinuation of anticoagulant therapy. Positive aCL and/or anti-β2GPI at the time of acute DVT have a strong positive predictive value for APS and may support therapeutic decisions.

The clinical significance of a shortened activated partial thromboplastin time in patients with connective tissue disease

INTRODUCTION

Connective tissue disease (CTD) patients have been reported to have an increased risk of venous thromboembolism (VTE). Deep venous thrombosis represents a potential emergency that may have a fatal outcome. The D-dimer test is the most widely accepted screening marker for VTE; however, elevation of the plasma D-dimer level without demonstrable thrombosis sometimes accompanies CTD activity itself, infection, and other conditions. Thus, the accuracy of a diagnosis of VTE based on a D-dimer test result is lower in CTD patients. The activated partial thromboplastin time (APTT) test is a very common and simple test.

METHOD

The medical records of 535 CTD patients were retrospectively investigated. The following data were extracted: APTT, D-dimer, thrombotic events, laboratory data, and systemic corticosteroid therapy.

RESULTS

The rates of thrombotic events and VTE were significantly increased in patients with a shortened APTT (< 26 s) (PSAPTT) in comparison to those without a shortened APTT (p = 0.004, 0.0009, respectively). The number of PSAPTTs was significantly increased in patients with VTE in comparison to those without VTE (p = 0.0009). In the diagnosis of VTE in CTD patients, the specificity and positive predictive value (PPV) of the D-dimer test were 71.6% and 83.8% and 12.7% and 19.4%, respectively. The combination of a shortened APTT and elevated plasma D-dimer level improved the specificity and PPV to 94.7% and 97.3% and to 25.0% and 36.4%, respectively.

CONCLUSIONS

For the evaluation of possibility of accompanying VTE in CTD patients, APTT shortened was useful and should be evaluated with careful attention.

KEY POINTS

• Regarding the specificity for diagnosing VTE in CTD patients, a shortened APTT showed a value (84.3%) comparable or superior to that of the D-dimer test. • The combination of a shortened APTT and elevated D-dimer level improved the specificity of the diagnosis of VTE in CTD patients to (94.7% or 97.3%) in comparison to the D-dimer test alone (71.6% or 83.8%). • The positive predictive value of the combination of a shortened APTT and plasma D-dimer elevation for the diagnosis of VTE in CTD patients increased to 25.0% or 36.4%. • In the management of CTD patients, physicians should pay attention when they encounter patients with a shortened APTT, as it may indicate VTE.

Monitoring of anticoagulation in thrombotic antiphospholipid syndrome

Anticoagulation is central to the management of thrombotic antiphospholipid syndrome (APS). The standard anticoagulant treatment for thrombotic APS is life-long warfarin or an alternative vitamin K antagonist. The role of direct oral anticoagulants for thrombotic APS is not established due to the lack of definitive evidence and has recently been addressed in international guidance. Other anticoagulant options include low molecular weight heparin, unfractionated heparin, and fondaparinux. In APS patients, lupus anticoagulant can affect phospholipid-dependent coagulation monitoring tests, so that they may not reflect true anticoagulation intensity. Accurate assessment of anticoagulation intensity is essential, to optimize anticoagulant dosing and facilitate thrombus resolution; minimize the risk of recurrent thrombosis or bleeding; inform assessment of whether recurrent thrombosis is related to breakthrough thrombosis while on therapeutic anticoagulation, subtherapeutic anticoagulation, non-adherence, or spurious results; and guide the management of bleeding. Knowledge of anticoagulant intensity also informs assessment and comparison of anticoagulation regimens in clinical studies. Considerations regarding anticoagulation dosing and/or monitoring of thrombotic APS patients underpin appropriate management in special situations, notably APS-related severe renal impairment, which can occur in APS or APS/systemic lupus erythematosus-related nephropathy or catastrophic APS; and APS-related thrombocytopenia. Anticoagulant dosing and monitoring in thrombotic APS patients also require consideration in anticoagulant-refractory APS and during pregnancy. In this review, we summarize the tests generally used in monitoring anticoagulant therapy, use of the main anticoagulants considered for thrombotic APS, lupus anticoagulant effects on anticoagulation monitoring tests, and strategies for appropriate anticoagulant monitoring in thrombotic APS.

Thrombotic antiphospholipid syndrome: A practical guide to diagnosis and management

Thrombotic antiphospholipid syndrome (APS) is characterised by venous, arterial and/or small vessel thrombosis in the context of persistently positive antiphospholipid antibodies (aPL). The diagnosis and management of thrombotic APS continues to prove challenging for clinicians. We provide a practical guide to the diagnosis of APS including who to test for aPL and which tests to do. We also consider clinical practice points on the management of venous, arterial and small vessel thrombosis, in the context of first and recurrent thrombotic events. Non-criteria manifestations of APS are reviewed. An approach to recurrent thrombosis and anticoagulant-refractory APS is discussed, with options including increasing the anticoagulation intensity of vitamin K antagonists, switching to low-molecular-weight-heparin, the use of fondaparinux and/or the addition of antiplatelet treatment. Adjunctive options such as vitamin D, hydroxychloroquine and statins are also addressed.

Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis: Update of the guidelines for lupus anticoagulant detection and interpretation

This guidance focuses on methodological aspects of lupus anticoagulant (LA) testing, as well as interpretation of results for clinicians. The main changes in how to test for LA compared with the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee 2009 guidelines, in the preanalytical phase are more detailed recommendations on how to handle testing in anticoagulated patients, and the timing of testing. Also, routine coagulation tests are advised to obtain more information on the coagulation background of the patient, and when necessary, anti-Xa activity measurement for heparins or specific assays for direct oral anticoagulants should be performed. The three-step procedure with two test systems (diluted Russell's viper venom time and activated partial thromboplastin time [aPTT]) is essentially not changed. Silica remains the preferable activator in the aPTT assays, but ellagic acid is not excluded. We advise simultaneous performance of the mixing and confirmatory step, in each sample with a prolonged screening test. The confirmatory step can also be performed on a mixture of patient plasma and normal pooled plasma. Cutoff values should be established in-house on at least 120 normals, with transference of the manufacturer's cutoffs as an alternative. Reporting of results has not been changed, although more attention is focused on what clinicians should know. Patient selection for LA testing has been expanded.

Monitoring unfractionated heparin therapy: Lack of standardization of anti-Xa activity reagents

INTRODUCTION

One of the main advantages of using anti-Xa instead of activated partial thromboplastin time in monitoring of unfractionated heparin (UFH) therapy relies on its hypothesized standardization, with a unique therapeutic range defined to be 0.30 to 0.70 IU/mL. The aim of the present study was to compare the inter-reagent agreement of anti-Xa activity.

METHODS

Citrate tubes were obtained from 104 inpatients on UFH. Plasma samples were stored frozen in aliquots at -70°C before being shipped to three accredited coagulation laboratories to be evaluated for anti-Xa activity using their routine assay(s). Pooled normal plasmas spiked with dilutions of the 6th International Standard of UFH to achieve anti-Xa activities up to 1.0 IU/mL were evaluated using the same techniques.

RESULTS

In the plasmas from patients on UFH, the median anti-Xa activity ranged from 0.37 IU/mL with one reagent to 0.57 IU/mL with another; results were in between (0.45 IU/mL) using two other reagents. Comparisons of results obtained using the different reagents demonstrated unacceptable bias up to 0.24 IU/mL between some reagents (41% difference). The concordance as whether anti-Xa activities measured using different reagents were within or outside the therapeutic range was between 0.411 and 0.939 (kappa). Similar discrepancy was demonstrated for anti-Xa activities when evaluating normal plasma spiked with the International Standard. A discrepancy of the same order of magnitude was demonstrated in the 2017 External Quality Assessment Program provided by the External Quality Control in Assays and Tests exercises.

CONCLUSIONS

The reported discrepancy between test results obtained using different anti-Xa assays clearly suggests a lack of standardization of that assay with potentially significant impact on the patients' anticoagulation.

Lupus anticoagulant detection in anticoagulated patients. Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis

BACKGROUND

The laboratory detection of lupus anticoagulants (LA) in anticoagulated patients represents a challenge and there is no consensus on the types of assays/procedures to be adopted.

OBJECTIVES

This communication of the International Society on Thrombosis and Haemostasis (ISTH), Scientific and Standardization Committee (SSC) aims to give guidance on the procedures to be adopted.

METHODS

Members of the ISTH-SSC on Lupus Anticoagulant/Antiphospholipid Antibodies reviewed the literature to search for evidence on the most appropriate assays/procedures to be adopted.

RESULTS

Anticoagulants are able to interfere with the tests used for LA detection, giving rise to occasional false-positive or false-negative LA. Some commercial tests include in their composition heparin-neutralizers able to quench unfractionated or low molecular weight heparin up to 1.0 U/mL. LA tests are less affected by low molecular weight heparin, but caution is needed in the interpretation of results. Vitamin K antagonists (VKAs) may affect LA detection. Dilution of test plasma into pooled normal plasma is not a reliable solution as false-negative or false-positive LA may occur. Direct oral anticoagulants (DOACs) affect LA detection. Hence, it is not recommended to attempt LA detection in those patients. The use of DOAC adsorbents is a promising solution and should be further investigated on LA-positive and LA-negative patient populations. Taipan/Ecarin tests may be a solution for VKAs and anti-FXa DOACs, but independent evidence on their value and standardized kits is needed.

CONCLUSIONS

LA detection during anticoagulation remains a challenge, especially for VKAs. DOAC removal by in vitro addition to plasma of appropriate absorbents is promising.

Development of an electrospun biomimetic polyurea scaffold suitable for vascular grafting

The optimization of biomechanical and biochemical properties of a vascular graft to render properties relevant to physiological environments is a major challenge today. These critical properties of a vascular graft not only regulate its stability and integrity, but also control invasion of cells for scaffold remodeling permitting its integration with native tissue. In this work, we have synthesized a biomimetic scaffold by electrospinning a blend of a polyurea, poly(serinol hexamethylene urea) (PSHU), and, a polyester, poly-ε-caprolactone (PCL). Mechanical properties of the scaffold were varied by varying polymer blending ratio and electrospinning flow rate. Mechanical characterization revealed that scaffolds with lower PSHU content relative to PCL content resulted in elasticity close to native mammalian arteries. We also found that increasing electrospinning flow rates also increased the elasticity of the matrix. Optimization of elasticity generated scaffolds that enabled vascular smooth muscle cells (SMCs) to adhere, grow and maintain a SMC phenotype. The 30/70 scaffold also underwent slower degradation than scaffolds with higher PSHU content, thereby, providing the best option for in vivo remodeling. Further, Gly-Arg-Gly-Asp-Ser (RGD) covalently conjugated to the polyurea backbone in 30/70 scaffold resulted in significantly increased clotting times. Reducing surface thrombogenicity by the conjugation of RGD is critical to avoiding intimal hyperplasia. Hence, biomechanical and biochemical properties of a vascular graft can be balanced by optimizing synthesis parameters and constituent components. For these reasons, the optimized RGD-conjugated 30/70 scaffold electrospun at 2.5 or 5 mL/h has great potential as a suitable material for vascular grafting applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 278-290, 2018.

Evaluation of Potential Clinical Surrogate Markers of a Trauma Induced Alteration of Clotting Factor Activities

Objective. The aim of this study was to identify routinely available clinical surrogate markers for potential clotting factor alterations following multiple trauma. Methods. In 68 patients admitted directly from the scene of the accident, all soluble clotting factors were analyzed and clinical data was collected prospectively. Ten healthy subjects served as control group. Results. Patients showed reduced activities of clotting factors II, V, VII, and X and calcium levels (all P < 0.0001 to 0.01). Levels of hemoglobin and base deficit correlated moderately to highly with the activities of a number of clotting factors. Nonsurvivors and patients who needed preclinical intubation or hemostatic therapy showed significantly reduced factor activities at admission. In contrast, factor VIII activity was markedly elevated after injury in general (P < 0.0001), but reduced in nonsurvivors (P < 0.05). Conclusions. Multiple trauma causes an early reduction of the activities of nearly all soluble clotting factors in general. Initial hemoglobin and, with certain qualifications, base deficit levels demonstrated a potential value in detecting those underlying clotting factor deficiencies. Nevertheless, their role as triggers of a hemostatic therapy as well as the observed response of factor VIII to multiple trauma and also its potential prognostic value needs further evaluation.

Statistical methods used to test for agreement of medical instruments measuring continuous variables in method comparison studies: a systematic review

Background

Accurate values are a must in medicine. An important parameter in determining the quality of a medical instrument is agreement with a gold standard. Various statistical methods have been used to test for agreement. Some of these methods have been shown to be inappropriate. This can result in misleading conclusions about the validity of an instrument. The Bland-Altman method is the most popular method judging by the many citations of the article proposing this method. However, the number of citations does not necessarily mean that this method has been applied in agreement research. No previous study has been conducted to look into this. This is the first systematic review to identify statistical methods used to test for agreement of medical instruments. The proportion of various statistical methods found in this review will also reflect the proportion of medical instruments that have been validated using those particular methods in current clinical practice.

Methodology/Findings

Five electronic databases were searched between 2007 and 2009 to look for agreement studies. A total of 3,260 titles were initially identified. Only 412 titles were potentially related, and finally 210 fitted the inclusion criteria. The Bland-Altman method is the most popular method with 178 (85%) studies having used this method, followed by the correlation coefficient (27%) and means comparison (18%). Some of the inappropriate methods highlighted by Altman and Bland since the 1980s are still in use.

Conclusions

This study finds that the Bland-Altman method is the most popular method used in agreement research. There are still inappropriate applications of statistical methods in some studies. It is important for a clinician or medical researcher to be aware of this issue because misleading conclusions from inappropriate analyses will jeopardize the quality of the evidence, which in turn will influence quality of care given to patients in the future.

Dynamic APTT parameters: applications in thrombophilia

BACKGROUND

Patients with a history of venous thrombosis occasionally have shortened APTTs when compared with those of healthy references, but the clinical applicability of a shortened APTT is limited.

OBJECTIVES

The present study aimed to characterize dynamic APTT profiles in patients with previously documented venous thrombosis and hypothesized that the APTT-MaxVel was significantly elevated in patients with a history of venous thrombosis as compared with healthy controls.

METHODS

We performed a case control study, enrolling a total of 38 patients, 17 males and 21 females, with a verified recent venous thrombotic event, as well as 88 healthy controls. Fifty-three per cent of patients were found to have a biochemical risk factor. A standard APTT was recorded in platelet-poor plasma, and the digital clotting signal was processed using simple algorithms developed to derive dynamic coagulation parameters.

RESULTS

Patients had a significantly higher mean APTT-MaxVel (195.5 s(-1) ; SD = 57; 95% CI, 176.8-214.1) as compared with healthy controls (137.3 s(-1) ; SD = 21; 95% CI, 130.7-143.8). Patients also had significantly shorter mean APTTs (26.9 s; SD = 3.2; 95% CI, 25.9-28.0) than healthy controls (28.5 s; SD = 2.8; 95% CI, 27.9-29.0). While only one out of 38 patients (2.6%) had a standard APTT below the lower reference interval, 15 of the 38 patients (38.5%) had an APTT-MaxVel above the upper reference limit. Regression analysis revealed linear correlation between FVIII:C, the level of fibrinogen and APTT-MaxVel (R(2) = 0.89, P < 0.05).

CONCLUSIONS

Simple signal processing of the APTT and the use of dynamic parameters represents a stronger predictive marker for hypercoagulation in patients with verified venous thrombosis than the standard APTT measurement.

Shortened activated partial thromboplastin time: causes and management

Throughout the long history of the hemostasis laboratory, and as an evaluation of the coagulation cascade, the results of the activated partial thromboplastin time (APTT) have primarily been considered as an index of loss-of-function and rarely as an index of gain-of-function. Nevertheless, there are now several clinical and technical reasons that no longer allow us to simply ignore or overlook shortened APTTs in laboratory practice. It has long been suspected that the leading cause of shortened APTTs are related to preanalytical problems, in which case it would be inappropriate for a laboratory to issue such a test result, which would expectedly not adequately mirror the patient's true condition. Should such artifactual results be reliably ruled out, that is by confirming short APTT values on subsequent samples, it would then be worth considering to troubleshoot potential causes, inasmuch as this phenomenon may reflect a variety of clinically meaningful conditions, including an increased risk of thromboembolic events, cancer, myocardial infarction, thyroid disorders, diabetes, and pregnancy. Although there are no univocal data supporting the origin of this singular phenomenon as yet, we strongly encourage the utility of postanalytical laboratory guidance, including a relevant short accompanying comment in the laboratory report linked to the APTT test result, for example, noting 'Short APTT-potentially reflective of in-vitro activation of blood coagulation due to difficult collection. If the value is systematically confirmed in subsequent samples, please contact the laboratory to help assess the cause'.

Shortened activated partial thromboplastin time, a hemostatic marker for hypercoagulable state during acute coronary event

Various factors may contribute to a hypercoagulable state and acute vascular thrombosis. A prospective study was conducted involving 165 coronary heart disease (CHD) patients from the Cardiology Unit, Hospital Universiti Sains Malaysia. The purpose of this study was to investigate the relationship among factor VIII (FVIII), prothrombin time (PT), activated partial thromboplastin time (APTT), and activated protein C resistance (APC-R) state among CHD patients and to look for potential clinical applications from these laboratory findings. There were 110 cases diagnosed as acute coronary syndrome (ACS), whereas another 55 were stable coronary artery disease (SCAD) patients. PT, APTT, FVIII, and APC-R assays were performed on all subjects. There was a significant difference between the FVIII level and the APTT results (P value < 0.0001). A negative relationship was found between the FVIII level and the APTT from linear regression analysis (R(2) = 10%, P value < 0.0001). For each 1% increase in the FVIII level, the APTT was reduced by 0.013 s (95% confidence interval (CI) between -0.019 and -0.007). Interestingly, none of the SCAD patients had abnormally short APTT. Approximately 68.4% of cases with a positive APC-R assay were found to have a high FVIII level. In conclusion, the APTT test is a potential hemostatic marker for hypercoagulable state including in arterial thrombosis.

A laboratory evaluation into the short activated partial thromboplastin time

Although short activated partial thromboplastin times (APTTs) are generally considered to be laboratory artefacts of problematic blood collections, there is mounting evidence that in some cases a short APTT may reflect a hypercoagulable state, potentially associated with increased thrombotic risk and adverse cardiovascular events. We prospectively evaluated the phenomenon of short APTTs in 113 consecutive samples compared with an equal number of age and sex-matched normal APTT samples. We found a significant difference in various test parameters including prothrombin time (PT), Factor (F) V, FVIII, FXI, FXII, von Willebrand factor (VWF) antigen and collagen-binding activity, and in the level of procoagulant phospholipids, as assessed using a novel assay procedure (XACT). Interestingly, there was a significant negative association for fibrinogen, and although elevated, there was no significant association for FIX. On the basis of identified consecutive samples having multiple low APTTs on several sequential days, a proportion of laboratory-defined short APTTs appear to represent in-vivo hypercoagulability. In conclusion, plasma from patients presenting with short APTTs is reflective of a complex hypercoagulant milieu that could feasibly contribute to thrombotic risk, and 20% or more of laboratory definable short APTTs appear to reflect in-vivo phenomenon.

Prothrombin time and partial thromboplastin time assay considerations

Prothrombin times and activated partial thromboplastin times have long been used as tests of overall ("global") clotting function. Laboratory coagulation testing issues should be at the forefront of the reader's consciousness whenever critically evaluating and extrapolating published study conclusions reliant on the results of these tests. Thus, this article reviews laboratory issues and known variables influencing prothrombin time and partial thromboplastin time results and international normalized ratio determinations.

Alterations in some blood coagulation parameters in naturally occurring cases of canine babesiosis

Changes in coagulation parameters were studied in dogs naturally infected with Babesia canis canis (n = 30), and haemostasis was evaluated and compared to values obtained from healthy dogs (n = 29). To date, there have not been any studies examining the dynamics of thrombin-antithrombin complex formation in cases of canine babesiosis. Coagulation parameters evaluated before (day 0) and on days 1, 2, and 3 after treatment with imidocarb (6 mg/kg inj. s.c.) included the determination of platelet counts, the formation of thrombin-antithrombin complexes (TAT), prothrombin time (PT), activated partial thromboplastin time (APTT) and antithrombin III (AT III) activity. TAT complexes were significantly elevated in animals with babesiosis on days 0 and 2 (mean 49.7 and 87.7 microg/L vs. control, 7.2 microg/L). AT III activity was significantly decreased at all time-points examined. There were no differences in PT. On days 2 and 3 the APTT was significantly shortened in the infected dogs when compared to control animals (means of 21.3 and 19.2 s vs. control, 30.0 s). Our analysis demonstrated that infected dogs had significant thrombocytopenia during the course of the study (mean day 0 - 29 x 10(9) /L, day 1 - 48 x 10(9) /L, day 2 - 47 x 10(9) /L and day 3 - 87 x 10(9) /L, vs. control -259 x 10(9) /L). These data suggest that babesiosis in dogs compromise primary and secondary haemostasis and that induction of disseminated intravascular coagulation (DIC) occurs in canine babesiosis.

Covalent inactivation of factor VIII antibodies from hemophilia A patients by an electrophilic FVIII Analog

The antigen-binding sites of antibodies (Abs) can express enzyme-like nucleophiles that react covalently with electrophilic compounds. We examined the irreversible and specific inactivation of antibodies (Abs) to Factor VIII (FVIII) responsible for failure of FVIII replacement therapy in hemophilia A (HA) patients. Electrophilic analogs of FVIII (E-FVIII) and its C2 domain (E-C2) were prepared by placing the strongly electrophilic phosphonate groups at surface-exposed Lys side chains of diverse antigenic epitopes. IgG Abs to FVIII from HA patients formed stable immune complexes with E-FVIII and E-C2 that were refractory to dissociation by SDS treatment and boiling, procedures that dissociate noncovalent Ab-antigen complexes. The rate-limiting step in the reaction was formation of the initial noncovalent complexes. Conversion of the initial complexes to the irreversible state occurred rapidly. The antigenic epitopes of E-FVIII were largely intact, and most of the Abs were consumed covalently. E-FVIII expressed poor FVIII cofactor activity in clotting factor assays. Nonspecific interference by E-FVIII in clotting factor function was not evident. Treatment with E-FVIII, and to a lesser extent E-C2, irreversibly relieved the FVIII inhibitory effect of HA IgG in clotting factor assays. Small FVIII peptides did not display useful reactivity, highlighting the diverse epitope specificities of the Abs and the conformational character of FVIII epitopes. E-FVIII is a prototype reagent able to attain irreversible and specific inactivation of pathogenic Abs.