Apparent argatroban resistance in a patient with elevated factor VIII levels

Unresponsiveness of Activated Partial Thromboplastin Time to Bivalirudin in Adults Receiving Extracorporeal Membrane Oxygenation

Activated partial thromboplastin time (aPTT) is the standard for monitoring bivalirudin but demonstrates a nonlinear response at higher drug concentrations. The objective of this study was to assess the relationship between bivalirudin dose and aPTT in patients receiving extracorporeal membrane oxygenation (ECMO) to determine a threshold where aPTT unresponsiveness occurs. Two hundred fourteen adults receiving bivalirudin during ECMO between 2018 and 2022 were included. Piecewise regression in a linear mixed effects model was used to determine a bivalirudin dose threshold of 0.21 mg/kg/hr for aPTT unresponsiveness. For doses of less than 0.21 mg/kg/hr (n = 135), every 0.1 mg/kg/hr dose increase led to an aPTT increase of 11.53 (95% confidence interval [CI] = 9.85-13.20) seconds compared to only a 3.81 (95% CI = 1.55-6.06) seconds increase when dose was greater than or equal to 0.21 mg/kg/hr (n = 79) (pinteraction < 0.001). In multivariable logistic regression, venovenous configuration (odds ratio [OR] = 2.83, 95% CI = 1.38-5.77) and higher fibrinogen concentration (OR = 1.22, 95% CI = 1.05-1.42) were associated with greater odds of unresponsiveness, whereas older age (OR = 0.79, 95% CI = 0.63-0.98), kidney dysfunction (OR = 0.48, 95% CI = 0.25-0.92), and a higher baseline aPTT (OR = 0.89, 95% CI = 0.82-0.97) were associated with lower odds. Alternative methods are necessary to ascertain bivalirudin's hemostatic impact when doses exceed 0.21 mg/kg/hr during ECMO.

Argatroban Resistance and Successful Adjunctive Anticoagulation for Cerebral Venous Sinus Thrombosis WithSERPINC1Mutation

Objectives

Anticoagulation therapy for cerebral venous sinus thrombosis (CVST) with antithrombin (AT) deficiency due toSERPINC1mutation does not often yield the expected outcomes. Argatroban may be effective for thrombophilia caused bySERPINC1mutation. However, argatroban resistance deserves attention.

Methods

We report a case of a 19-year-old man who was admitted to the hospital with sudden headache, nausea, vomiting, and eye swelling for 3 days. Brain MRI on admission showed multifocal CVST.

Results

SERPINC1mutation (exon1, c.40delA: [p.R14Gfs*17]) combined with hereditary AT deficiency (AT activity was 50% [reference range: 80%–120%]) was detected in this patient. A high dose of anticoagulation treatment with argatroban did not improve the activated partial thromboplastin time (APTT) level to the target range (1.5–3 times over the initial baseline level) for this case. We chose adjunctive anticoagulation (argatroban-combined low-molecular-weight heparin), and the APTT gradually reached the target level. At 3-month follow-up, no recurrence of headache or any systemic hemorrhage was found and the ultrasonography of the optic nerve sheath showed normal. Magnetic resonance black blood thrombosis imaging suggested thrombus absorption.

Discussion

Argatroban resistance may be associated with thrombin receptor saturation and deserves attention. The use of adjunctive anticoagulants may be the optimum strategy during acute and subacute phases of CVST with AT deficiency due toSERPINC1mutation.

Heparin Resistance in SARS-CoV-2 Infected Patients with Venous Thromboembolism

Introduction: Heparin resistance has been reported in coronavirus disease 2019 (COVID-19) patients receiving intravenous unfractionated heparin (IV UFH). Anti-Xa monitoring of IV UFH has been suggested over activated partial thromboplastin times due to laboratory interference from elevated factor VIII and fibrinogen levels in COVID-19 patients. Information on heparin resistance with anti-Xa monitoring in COVID-19 patients with confirmed venous thromboembolism (VTE) is lacking. Methods: In this retrospective cohort study of patients with radiographically confirmed VTE, IV UFH dosage requirements in COVID-19 positive patients were compared with COVID-19 negative patients. The primary endpoint was the IV UFH dose needed to achieve a therapeutic anti-Xa level. Secondary endpoints included time to therapeutic anti-Xa, number of dose adjustments to achieve therapeutic anti-Xa, and bleeding. Results: Sixty-four patients with confirmed VTE were included (20 patients COVID-19 positive, 44 patients COVID-19 negative). Eighty-five percent (17 of 20) of COVID-19 positive patients achieved anti-Xa ≥ 0.3 units/mL with the first anti-Xa level drawn post-IV UFH infusion initiation. The median UFH dose needed to achieve first therapeutic anti-Xa was similar between COVID-19 positive and COVID-19 negative patients (median [IQR]: 18 units/kg/hour [18-18] vs 18 units/kg/hour [18-18], P = .423). The median number of dose adjustments and time to achieve therapeutic anti-Xa were also similar between the 2 groups. The frequency of patients receiving IV UFH of more 35 000 units/day did not differ between the 2 groups. Two cases of clinically significant heparin resistance in the COVID-19 positive group were identified. Conclusions: During the first wave of COVID-19, heparin dose and time to therapeutic anticoagulation appeared to be similar between COVID-19 positive and COVID-19 negative patients monitored by anti-Xa at our institution. More studies are required to evaluate clinically significant heparin resistance in the context of the wide range of viral variants which developed, and beyond the population observed in this single center retrospective study.

Caution in Using the Activated Partial Thromboplastin Time to Monitor Argatroban in COVID-19 and Vaccine-Induced Immune Thrombocytopenia and Thrombosis (VITT)

Introduction

Argatroban is licensed for patients with heparin-induced thrombocytopenia and is conventionally monitored by activated partial thromboplastin time (APTT) ratio. The target range is 1.5 to 3.0 times the patients’ baseline APTT and not exceeding 100 s, however this baseline is not always known. APTT is known to plateau at higher levels of argatroban, and is influenced by coagulopathies, lupus anticoagulant and raised FVIII levels. It has been used as a treatment for COVID-19 and Vaccine-induced Immune Thrombocytopenia and Thrombosis (VITT). Some recent publications have favored the use of anti-IIa methods to determine the plasma drug concentration of argatroban.

Methods

Plasma of 60 samples from 3 COVID-19 patients and 54 samples from 5 VITT patients were tested by APTT ratio and anti-IIa method (dilute thrombin time dTT). Actin FS APTT ratios were derived from the baseline APTT of the patient and the mean normal APTT.

Results

Mean APTT ratio derived from baseline was 1.71 (COVID-19), 1.33 (VITT) compared to APTT ratio by mean normal 1.65 (COVID-19), 1.48 (VITT). dTT mean concentration was 0.64 µg/ml (COVID-19) 0.53 µg/ml (VITT) with poor correlations to COVID-19 baseline APTT ratio r² = 0.1526 p <0.0001, mean normal r² = 0.2188 p < 0.0001; VITT baseline APTT ratio r² = 0.04 p < 0.001, VITT mean normal r² = 0.0064 p < 0.001.

Conclusions

We believe that dTT is a superior method to monitor the concentration of argatroban, we have demonstrated significant differences between APTT ratios and dTT levels, which could have clinical impact. This is especially so in COVID-19 and VITT.

GFHT Proposals On The Practical Use Of Argatroban - With Specifics Regarding Vaccine-Induced Immune Thrombotic Thrombocytopaenia (VITT)

Argatroban is a direct anti-IIa (thrombin) anticoagulant, administered as a continuous intravenous infusion; it has been approved in many countries for the anticoagulant management of heparin-induced thrombocytopaenia (HIT). Argatroban was recently proposed as the non-heparin anticoagulant of choice for the management of patients diagnosed with Vaccine-induced Immune Thrombotic Thrombocytopaenia (VITT). Immunoglobulins are also promptly intravenously administered in order to rapidly improve platelet count; concomitant therapy with steroids is also often considered. An ad hoc committee of the French Working Group on Haemostasis and Thrombosis members has worked on updated and detailed proposals regarding the management of anticoagulation with argatroban, based on previously released guidance for HIT, and adapted for VITT. In case of VITT, the initial dose to be preferred is 1.0 µg x kg^-1 x min^-1, with further dose-adjustments based on iterative and frequent clinical and laboratory assessments. It is strongly advised to involve a health practitioner experienced in the management of difficult cases in haemostasis. The first laboratory assessment should be performed 4 hours after the initiation of argatroban infusion, with further controls at 2-4-hour intervals until steady state, and at least once daily thereafter. Importantly, full anticoagulation should be rapidly achieved in case of widespread thrombosis. Cerebral vein thrombosis (which is typical of VITT) should not call for an overly cautious anticoagulation scheme. Argatroban administration requires baseline laboratory assessment and should rely on an anti-IIa assay to derive argatroban plasma levels using a dedicated calibration, with a target range between 0.5 and 1.5 µg/mL. Target argatroban plasma levels can be refined based on meticulous appraisal of risk factors for bleeding and thrombosis, on frequent reassessments of clinical status with appropriate vascular imaging, and on the changes in daily platelet counts. Regarding the use of aPTT, baseline value and possible causes for alterations of the clotting time must be taken into account. Specifically, in case of VITT, an aPTT ratio (patient's / mean normal clotting time) between 1.5 and 2.5 is suggested, to be refined according to the sensitivity of the reagent to the effect of a direct thrombin inhibitor. The sole use of aPTT is discouraged: one has to resort to a periodical check with an anti-IIa assay at least, with the help of a specialised laboratory if necessary. Dose modifications should proceed in a stepwise manner with 0.1 to 0.2 µg x kg^-1 x min^-1 up- or downward changes, taking into account the initial dose, laboratory results, and the whole individual setting. Nomograms are available to adjust the infusion rate. Haemoglobin level, platelet count, fibrinogen plasma level and liver tests should be periodically checked, depending on the clinical status, the more so when unstable.

Argatroban versus heparin in patients without heparin-induced thrombocytopenia during venovenous extracorporeal membrane oxygenation: a propensity-score matched study

BACKGROUND

During venovenous extracorporeal membrane oxygenation (vvECMO), direct thrombin inhibitors are considered by some potentially advantageous over unfractionated heparin (UFH). We tested the hypothesis that Argatroban is non-inferior to UFH regarding thrombosis and bleeding during vvECMO.

METHODS

We conducted a propensity-score matched observational non-inferiority study of consecutive patients without heparin-induced-thrombocytopenia (HIT) on vvECMO, treated between January 2006 and March 2019 in the medical intensive care unit at the University Hospital Regensburg. Anticoagulation was realized with UFH until August 2017 and with Argatroban from September 2017 onwards. Target activated partial thromboplastin time was 50 ± 5seconds in both groups. Primary composite endpoint was major thrombosis and/or major bleeding. Major bleeding was defined as a drop in hemoglobin of ≥ 2 g/dl/day or in transfusion of ≥ 2 packed red cells/24 h, or retroperitoneal, cerebral, or pulmonary bleeding. Major thrombosis was defined as obstruction of > 50% of the vessel lumen diameter by means of duplex sonography. We also assessed technical complications such as oxygenator defects or pump head thrombosis, the time-course of platelets, and the cost of anticoagulation (including HIT-testing).

RESULTS

Out of 465 patients receiving UFH, 78 were matched to 39 patients receiving Argatroban. The primary endpoint occurred in 79% of patients in the Argatroban group and in 83% in the UFH group (non-inferiority for Argatroban, p = 0.026). The occurrence of technical complications was equally distributed (Argatroban 49% vs. UFH 42%, p = 0.511). The number of platelets was similar in both groups before ECMO therapy but lower in the UFH group after end of ECMO support (median [IQR]: 141 [104;198]/nl vs. 107 [54;171]/nl, p = 0.010). Anticoagulation costs per day of ECMO were higher in the Argatroban group (€26 [13.8;53.0] vs. €0.9 [0.5;1.5], p < 0.001) but not after accounting for blood products and HIT-testing (€63 [42;171) vs. €40 [17;158], p = 0.074).

CONCLUSION

In patients without HIT on vvECMO, Argatroban was non-inferior to UFH regarding bleeding and thrombosis. The occurrence of technical complications was similarly distributed. Argatroban may have less impact on platelet decrease during ECMO, but this finding needs further evaluation. Direct drug costs were higher for Argatroban but comparable to UFH after accounting for HIT-testing and transfusions.

Anticoagulation in ECMO patients: an overview

Extracorporeal membrane oxygenation (ECMO) is a form of cardiorespiratory support, and is being increasingly used to support refractory heart and respiratory failure. It involves draining blood from the vascular system, which is then circulated outside the body by a mechanical pump and then later reinfused back into the circulation. The blood that is circulated outside the body comes in contact with a large surface area of non-endothelial biosurface. This exposure leads to a pro-thrombotic state, and hence anticoagulation is required. Unfractionated heparin is the most commonly used anticoagulation in most ECMO centers, but it does require close monitoring. Despite the advances made, hemostasis remains a challenge for physicians who manage patients on ECMO.

Early Identification of Argatroban Resistance and the Consideration of Factor VIII

BACKGROUND

Argatroban, a synthetic, parenteral, nonheparin anticoagulant, is a direct thrombin inhibitor indicated for the prophylaxis or treatment of venous thromboembolism (VTE) in patients with heparin-induced thrombocytopenia with thrombosis (HITT) and for use during percutaneous coronary intervention (PCI) in patients who have or are at risk for developing HITT. Although heparin resistance occurs in approximately 0.5% to 5% of heparin-treated patients and is well documented in the literature, argatroban resistance is limited to a single case report. The objective of this case is to describe a case in which argatroban resistance was suspected in a patient with critical limb ischemia.

METHODS

This is a case report of a single patient.

RESULTS

A 68-year-old female admitted for critical limb ischemia requiring vascular intervention was treated for presumed HITT with argatroban. A therapeutic activated partial thromboplastin time (aPTT) was not attained (31 seconds) despite multiple uptitrations of the dose to 2.8 μg/kg/min (adjusted based on the institutional protocol and with consideration of organ dysfunction). A coagulopathy workup revealed a high level of factor VIII (265%).

CONCLUSION

This case supports early assessment of factor VIII levels and the consideration of argatroban resistance and in patients who have a subtherapeutic aPTT, despite multiple increases in dose with an elevated factor VIII level. Early identification should prompt the use of an alternative anticoagulant to ensure efficacy.

Anticoagulation with direct thrombin inhibitors during extracorporeal membrane oxygenation

Use of extracorporeal membrane oxygenation to support patients with critical cardiorespiratory illness is increasing. Systemic anticoagulation is an essential element in the care of extracorporeal membrane oxygenation patients. While unfractionated heparin is the most commonly used agent, unfractionated heparin is associated with several unique complications that can be catastrophic in critically ill patients, including heparin-induced thrombocytopenia and acquired antithrombin deficiency. These complications can result in thrombotic events and subtherapeutic anticoagulation. Direct thrombin inhibitors (DTIs) are emerging as alternative anticoagulants in patients supported by extracorporeal membrane oxygenation. Increasing evidence supports DTIs use as safe and effective in extracorporeal membrane oxygenation patients with and without heparin-induced thrombocytopenia. This review outlines the pharmacology, dosing strategies and available protocols, monitoring parameters, and special use considerations for all available DTIs in extracorporeal membrane oxygenation patients. The advantages and disadvantages of DTIs in extracorporeal membrane oxygenation relative to unfractionated heparin will be described.

Successful use of fondaparinux in the setting of heparin-induced thrombocytopenia with thrombosis confirmed by serotonin-release assay and Factor V Leiden

WHAT IS KNOWN AND OBJECTIVE

The off-label use of fondaparinux in patients with heparin-induced thrombocytopenia with thrombosis (HITT) has historically been controversial. We present a case of successful fondaparinux use to treat HITT confirmed by the serotonin-release assay in the setting of other significant clotting and bleeding risk factors.

CASE SUMMARY

We report a 19-year-old male with a history of Factor V Leiden and recent neurosurgery treated with fondaparinux after developing HITT confirmed by the serotonin-release assay (SRA). The patient achieved full platelet recovery on fondaparinux and was successfully transitioned to warfarin therapy without further thrombotic nor bleeding complications.

WHAT IS NEW AND CONCLUSION

This case demonstrates a clear example of success of fondaparinux use to treat SRA-confirmed HITT in the setting of complicating factors and adds to the existing literature supporting the use of fondaparinux for HIT.

Monitoring of argatroban and lepirudin anticoagulation in critically ill patients by conventional laboratory parameters and rotational thromboelastometry - a prospectively controlled randomized double-blind clinical trial

Background

Argatroban or lepirudin anticoagulation therapy in patients with heparin induced thrombocytopenia (HIT) or HIT suspect is typically monitored using the activated partial thromboplastin time (aPTT). Although aPTT correlates well with plasma levels of argatroban and lepirudin in healthy volunteers, it might not be the method of choice in critically ill patients. However, in-vivo data is lacking for this patient population.

Therefore, we studied in vivo whether ROTEM or global clotting times would provide an alternative for monitoring the anticoagulant intensity effects in critically ill patients.

Methods

This study was part of the double-blind randomized trial “Argatroban versus Lepirudin in critically ill patients (ALicia)”, which compared critically ill patients treated with argatroban or lepirudin. Following institutional review board approval and written informed consent, for this sub-study blood of 35 critically ill patients was analysed. Before as well as 12, 24, 48 and 72 h after initiation of argatroban or lepirudin infusion, blood was analysed for aPTT, aPTT ratios, thrombin time (TT), INTEM CT,INTEM CT ratios, EXTEM CT, EXTEM CT ratios and maximum clot firmness (MCF) and correlated with the corresponding plasma concentrations of the direct thrombin inhibitor.

Results

To reach a target aPTT of 1.5 to 2 times baseline, median [IQR] plasma concentrations of 0.35 [0.01–1.2] μg/ml argatroban and 0.17 [0.1–0.32] μg/ml lepirudin were required. For both drugs, there was no significant correlation between aPTT and aPTT ratios and plasma concentrations. INTEM CT, INTEM CT ratios, EXTEM CT, EXTEM CT ratios, TT and TT ratios correlated significantly with plasma concentrations of both drugs. Additionally, agreement between argatroban plasma levels and EXTEM CT and EXTEM CT ratios were superior to agreement between argatroban plasma levels and aPTT in the Bland Altman analysis. MCF remained unchanged during therapy with both drugs.

Conclusion

In critically ill patients, TT and ROTEM parameters may provide better correlation to argatroban and lepirudin plasma concentrations than aPTT.

Trial registration

ClinicalTrials.gov, NCT00798525, registered on 25 Nov 2008

Electronic supplementary material

The online version of this article (10.1186/s12871-018-0475-y) contains supplementary material, which is available to authorized users.

Idiopathic catastrophic thrombosis with happy ending

A 59-year-old male patient suffered three life-threatening instent thromboses after an initial resuscitation due to an ST-segment elevation myocardial infarction of the anterior cardiac wall. With a high-risk profile for heparin-induced thrombocytopenia (HIT), he was placed on argatroban after the second reinfarction. Under this apparently appropriate treatment, a third reinfarction occurred, and the patient had to undergo high-risk cardiac bypass surgery. Later on, a deep vein thrombosis and an intracardiac thrombus formed. Despite a positive screening test for HIT and a single positive result in the heparin-induced platelet aggregation test, we are not convinced that HIT was the only underlying cause for this 'catastrophic thrombotic syndrome'. We speculate that a massive generation of thrombin, reflected in consistently high D dimers and the need of copious amounts of a direct thrombin inhibitor, triggered the set of events. With this case report, we want to raise awareness for cardiac complications in patients with complex clotting disorders and share our experience in the diagnostic and therapeutic management of such an unusual scenario.

Simultaneous Left Ventricular and Deep Vein Thrombi Caused by Protein C Deficiency

Protein C deficiency is a risk of venous thrombosis because of poor fibrinolytic activity. It remains controversial whether protein C deficiency causes arterial thrombosis. A 21-year-old woman was referred with a chief complaint of right leg pain and numbness. Contrast-enhanced computed tomography revealed a low-density mass in the left ventricle (LV), splenic infarction, and peripheral arterial obstructions in her right leg. Thrombosis extending from the renal vein to the inferior vena cava was also detected. Electrocardiography revealed ST depression in leads II, III, and aVF. Transthoracic echocardiography revealed hypokinesis of the apex and interventricular septum and a hypoechoic mass in the LV (26 × 20 mm). She was diagnosed with acute arterial obstruction caused by the LV thrombus, which might have resulted from previous myocardial infarction. Protein C activation turned out to be low (41%) 5 days after admission. The anticoagulant therapy was switched from heparin to rivaroxaban 16 days after admission. The LV thrombus disappeared 24 days after initial treatment, and she has had no thrombotic episodes for 2.8 years under rivaroxaban therapy. Thrombophilia should be investigated for cases of simultaneous left ventricular and deep venous thrombi. Rivaroxaban can be effective in prevention of further thrombotic events.

Elevated Factor VIII Levels Associated with Acute Graft Occlusion and Arterial and Venous Thrombosis After Off Pump CABG

Factor VIII is a common acute phase reactant and elevated levels confer an increased risk of thrombosis. Such thrombotic events have been documented in the literature, though to a limited extent. We present the case of a 54-year-old man presenting with a non-Q-wave myocardial infarction who was found to have triple vessel disease and subsequently underwent a 4-vessel coronary artery bypass grafting (CABG). Postoperatively, he was found to have multiple occluded vessels, deep vein thromboses, and a cerebrovascular accident (CVA). A hypercoagulability work-up revealed significantly elevated levels of factor VIII at 377% normal, which likely contributed to these thrombotic events. Further exploration is warranted to elucidate causal mechanisms of these thrombotic events, particularly of multiple graft occlusions, and to guide clinical decision making with regards to anticoagulation and stent management.

Direct Thrombin Inhibitor Resistance and Possible Mechanisms

Objective: To report 3 cases in which doses of bivalirudin higher than commonly used in clinical practice were required in order to achieve therapeutic anticoagulation as monitored by the activated partial thromboplastin time (aPTT). Case Summary: The medical records of 3 patients who required large doses of bivalirudin to remain therapeutic were thoroughly reviewed. In all 3 patients, bivalirudin was initiated at a rate appropriate for the patients' renal function and titrated using a nurse-driven protocol with recommended dose adjustments based on aPTT. Indications for bivalirudin were anticoagulation in intra-aortic balloon pump, treatment of deep vein thrombosis, and heparin-induced thrombocytopenia with thrombosis. Target aPTT was achieved between 25.5 and 134 hours after initiation despite appropriate titration intervals per protocol. Discussion: Bivalirudin is a direct thrombin inhibitor frequently used off-label for the medical management of heparin-induced thrombocytopenia. It typically exhibits predictable, dose-dependent anticoagulation. Heparin-induced thrombocytopenia was suspected in 2 of the 3 cases and confirmed in 1. In all 3 patients, target aPTT was initially achieved with doses between 0.456 and 1.0 mg/kg/h after a median of 30.7 hours; up to 1.8 mg/kg/h was required to maintain therapeutic aPTT. In 2 of the cases, the international normalized ratio also increased unexpectedly upon achievement of therapeutic aPTT values. Conclusion: Direct thrombin inhibitors may be subject to resistance mechanisms similar to those previously described in patients receiving heparin. The anticoagulation status of these patients remains unknown.

How I treat catastrophic thrombotic syndromes

Catastrophic thrombotic syndromes are characterized by rapid onset of multiple thromboembolic occlusions affecting diverse vascular beds. Patients may have multiple events on presentation, or develop them rapidly over days to weeks. Several disorders can present with this extreme clinical phenotype, including catastrophic antiphospholipid syndrome (APS), atypical presentations of thrombotic thrombocytopenic purpura (TTP) or heparin-induced thrombocytopenia (HIT), and Trousseau syndrome, but some patients present with multiple thrombotic events in the absence of associated prothrombotic disorders. Diagnostic workup must rapidly determine which, if any, of these syndromes are present because therapeutic management is driven by the underlying disorder. With the exception of atypical presentations of TTP, which are treated with plasma exchange, anticoagulation is the most important therapeutic intervention in these patients. Effective anticoagulation may require laboratory confirmation with anti–factor Xa levels in patients treated with heparin, especially if the baseline (pretreatment) activated partial thromboplastin time is prolonged. Patients with catastrophic APS also benefit from immunosuppressive therapy and/or plasma exchange, whereas patients with HIT need an alternative anticoagulant to replace heparin. Progressive thrombotic events despite therapeutic anticoagulation may necessitate an alternative therapeutic strategy. If the thrombotic process can be controlled, these patients can recover, but indefinite anticoagulant therapy may be appropriate to prevent recurrent events.

Comparison of the aPTT with alternative tests for monitoring direct thrombin inhibitors in patient samples

OBJECTIVES

The activated partial thromboplastin time (aPTT) test has been used for years to monitor parenteral direct thrombin inhibitors (DTIs) and unfractionated heparin. Because the aPTT correlates poorly with unfractionated heparin levels, we hypothesized that the aPTT may not be the best test for monitoring parenteral DTIs.

METHODS

Using 235 excess plasma specimens from 82 adult patients receiving treatment with DTIs (argatroban, bivalirudin, or dabigatran), we compared the aPTT with the ecarin chromogenic assay (ECA), the dilute thrombin time (dTT) test, and the prothrombinase-induced clotting time (PiCT) test.

RESULTS

The aPTT correlated poorly with each of the other tests in both bivalirudin- and argatroban-containing samples (r(2) = 0.04-0.23). The ECA and dTT exhibited the best correlations (r(2) = 0.66-0.93). Intermediate correlations were seen when the results of the PiCT were plotted against the dTT or ECA (r(2) = 0.46-0.58). Nineteen specimens obtained from six patients receiving dabigatran showed a good correlation between the dTT and the ECA (r(2) = 0.92).

CONCLUSIONS

The aPTT does not correlate well with other tests that might be used to monitor parental DTI administration. Further studies are needed to evaluate the clinical usefulness of alternative tests and their correlation with clinical outcomes.