Wayne L. Chandler

Circulating microparticles in neuropsychiatric systemic lupus erythematosus.

Phosphatidylserine‐rich microparticles derived from endothelial cells, platelets and leukocytes have been implicated as surrogate markers of cellular activation in systemic lupus erythematosus (SLE). Because microparticles have also been associated with many primary neurologic diseases, this study investigated whether cellular‐derived microparticles are also implicated in neuropsychiatric SLE (NPSLE).

Evaluation and Pharmacokinetics of Treatment Dose Enoxaparin in Hospitalized Patients With Morbid Obesity

Background: The pharmacokinetic properties of enoxaparin may lead to supratherapeutic antifactor Xa (anti-Xa) levels and increased bleeding when standard treatment doses are used in patients with morbid obesity. Objective: To evaluate the dose of enoxaparin needed to achieve therapeutic anti-Xa levels in a prospective, masked observational cohort of heterogeneous inpatients with morbid obesity and to determine whether patients with morbid obesity treated with 1 mg/kg of enoxaparin are at increased risk of supratherapeutic levels and bleeding events compared to patients receiving lower doses. Methods: Hospitalized patients with a body mass index ≥40 kg/m2 or actual body weight ≥140 kg and prescribed treatment doses of enoxaparin >60 mg per day were enrolled and consented to phlebotomy for determination of anti-Xa levels. Results: Forty-one patients were included for data analysis. The dose of enoxaparin that resulted in therapeutic and supratherapeutic anti-Xa levels at steady state was 0.83 mg/kg and 0.98 mg/kg (−0.11; 95% confidence interval [CI] −0.20 to −0.01, P = .02), respectively. Enoxaparin dose as mg/kg of actual body weight was an independent predictor of having a supratherapeutic anti-Xa level. Patients with doses <0.95 mg/kg versus ≥0.95 mg/kg were less likely to have supratherapeutic levels (odds ratio 0.21 [95% CI 0.05-0.84], P = .02) and had similar rates of subtherapeutic levels. Doses <0.95 mg/kg and ≥0.95 mg/kg resulted in similar bleeding rates of 17.9% and 22.2% (P = .71), respectively. Conclusion: Patients with morbid obesity required less than the recommended 1 mg/kg enoxaparin dose to achieve therapeutic peak anti-Xa levels; therefore, initiation with lower dosages is prudent and anti-Xa monitoring should guide dosage adjustments.

Alternative Monitoring of Argatroban Using Plasma-Diluted Thrombin Time

OBJECTIVE To report a case of heparin-induced thrombocytopenia (HIT) in a patient with concurrent liver dysfunction and a prolonged baseline activated partial thromboplastin time (aPTT) in whom argatroban therapy was monitored with aPTT and a novel plasma-diluted thrombin assay. CASE SUMMARY An 80-year-old man with HIT and liver dysfunction was treated with argatroban, which was initiated at a dose of 0.5 μg/kg/min and gradually decreased to 0.09 μg/kg/min. The patient had a mildly prolonged aPTT at baseline (37.5 seconds). He was concurrently monitored with aPTT, per institution protocol, and plasma-diluted thrombin time. Plasma-diluted thrombin times were consistently lower than aPTTs, but mirrored the trend of the aPTTs. Eleven hours after argatroban was stopped, the aPTT remained elevated (53.9 seconds), while the plasma-diluted thrombin time returned to normal range (26.4 seconds). The patients therapy was transitioned to warfarin and he had a hospital course with no thrombotic or bleeding complications. DISCUSSION Plasma-diluted thrombin time is a novel laboratory test consisting of 1 part patient plasma diluted with 3 parts normal plasma. Plasma-diluted thrombin time has been shown to blunt the sensitivity of the thrombin time and may be more accurate for drug monitoring. A MEDLINE search revealed 2 studies using the plasma-diluted thrombin time assay. The first study compared aPTT and plasma-diluted thrombin times in blood samples mixed with argatroban, bivalirudin, or lepirudin at 3 different concentrations. Blood samples contained lupus inhibitors, vitamin k deficiency, or normal baseline aPTTs. The aPTT overestimated drug concentrations in all samples with lupus anticoagulant and vitamin k deficiency, while the plasma-diluted thrombin time correctly estimated drug concentrations in nearly all samples. The second study looked at monitoring dabigatran with plasma-diluted thrombin time and found a linear relationship between the plasma-diluted thrombin time and the dabigatran dose-response curve. CONCLUSIONS Plasma-diluted thrombin time may be an alternative for direct thrombin inhibitor monitoring in patients with elevated aPTT values at baseline. Further randomized control trials are needed to determine its applicability in clinical practice.

Comparison of Clot-Based vs Chromogenic Factor Xa Procoagulant Phospholipid Activity Assays

We compared 2 commercial plasma procoagulant phospholipid activity (PPA) assays, chromogenic, using bound annexin V to capture phosphatidylserine-containing microparticles, and clot-based. In both, anionic phospholipids accelerated activation of prothrombin by factor Xa. PPA levels were lower in the chromogenic vs the clot-based assay, with poor correlation between methods: normal samples, mean ± SD, 27 ± 17 vs 590 ± 414 nmol/L (n = 24; r(2) = 0.29) and patient samples, mean ± SD, 45 ± 44 vs 401 ± 330 nmol/L (n = 51; r(2) = 0.26). Recovery of phosphatidylserine added to normal, heparinized, and warfarin plasma samples averaged 109% ± 39% using the chromogenic assay but was higher and more varied (mean ± SD, 176% ± 59%) in the clot-based assay. Lupus anticoagulants caused low recovery in both assays. Removal of microparticles by 0.22-μm filtration reduced PPA by 91% in the clot-based and 65% in the chromogenic assay. The clot-based assay showed higher correlation (r(2) = 0.82 vs 0.23) with flow cytometric platelet microparticle counts. The 2 assays measure different aspects of PPA in plasma, with the chromogenic assay primarily measuring smaller microparticles.

Platelet mapping assay interference due to platelet activation in heparinized samples.

OBJECTIVESnThromboelastography Platelet Mapping (TEGPM) is an assay designed to detect platelet inhibition due to aspirin or clopidogrel-like drugs. The purpose of this study was to evaluate potential causes of error in the design or operation of the assay.nnnMETHODSnWe evaluated percent inhibition of platelets due to aspirin or clopidogrel using TEGPM, which measures clot viscoelastic maximum amplitude (MA) after activation with adenosine diphosphate (ADP) or arachidonic acid (AA) and subtraction of MA due to fibrin (MAFibrin).nnnRESULTSnMAFibrin measured in heparinized blood showed an unstable increasing pattern in 28% of samples (16 of 58). The platelet aggregation inhibitor eptifibatide corrected increasing MAFibrin in 14 of 16 cases, while the thrombin inhibitor argatroban corrected increasing MAFibrin in six of 16 cases, suggesting that unanticipated platelet activation/ aggregation was a more important cause of unstable rising MAFibrin than uninhibited thrombin. The unstable increased MAFibrin falsely increased percent ADP inhibition on average from 19% to 38% and percent AA inhibition from 29% to 58%. Heparinized samples showed platelet clumping and had procoagulant platelet microvesicle levels double those in citrate anticoagulant.nnnCONCLUSIONSnUnanticipated platelet activation/aggregation occurring in the heparinized TEGPM samples lead to erroneous percent inhibition results.

Bleeding risks and response to therapy in patients with INR higher than 9.

An international normalized ratio (INR) higher than 9 is associated with a high risk of bleeding, yet most studies have focused on outpatients with lower INR. We retrospectively analyzed diagnosis, bleeding, treatment, and mortality in 162 patients with INR higher than 9, including inpatients and outpatients with and without warfarin treatment. Patients without anticoagulant treatment with INR higher than 9 had a poor prognosis, 67% experienced bleeding and 74% died. Among outpatients receiving warfarin with INR higher than 9, 11% had bleeding, but none died. Among inpatients receiving warfarin, 35% had bleeding and 17% died. Factors associated with bleeding were older age, renal failure, and alcohol use. Withholding warfarin or giving vitamin K treatment was ineffective at reducing the INR within 24 hours, whereas plasma infusion immediately dropped the INR to 2.4 ± 0.9. Because of underlying disease, comorbidities, and medications, hospitalized patients with INR higher than 9 may not respond quickly to withholding warfarin or vitamin K treatment, and plasma infusion may be needed to reduce INR and the risk of bleeding within 24 hours.

Platelet Function Assays—Not All Are Created Equal

Platelet function testing has undergone major changes in the last decade. In the past, these tests were primarily used to diagnose hereditary bleeding disorders, typically using a platelet aggregation assay. Although diagnosis of bleeding disorders is still important, measuring platelet function to monitor platelet inhibitor therapy has become the more common reason for ordering this type of testing. This has also led to a variety of new platelet function assays designed to assist platelet inhibitor monitoring. It is now clear that many patients show resistance to platelet inhibitor therapy. These patients show less platelet inhibition than expected for a given dose of medication, and an increased risk of thrombosis. The most common forms of resistance are related to clopidogrel and aspirin therapy. Several different resistance mechanisms have been described, but the most common is reduced metabolism of clopidogrel to its active form, leading to inadequate platelet inhibition. Reduced absorption of medications and receptor polymorphisms leading to reduced binding and inhibition by these drugs has also been reported. Two approaches have been taken to assess …

Anticoagulation Without Monitoring

The new oral anticoagulants dabigatran, rivaroxaban, and apixaban were developed and approved for use without the need for routine laboratory monitoring. With safety and efficacy profiles that are as good as or better than traditional anticoagulants that require monitoring, these medications are attractive alternatives for physicians and patients alike. The introduction of these new oral anticoagulants raises two important issues for the clinical laboratory: (1) under what clinical situations should plasma levels of these drugs be measured, and (2) how do we measure drugs designed to be used without monitoring when approved assays are not available and the need is for rapid turnaround times to help in the assessment of acute bleeding or thrombosis? This issue of the American Journal of Clinical Pathology contains two important review articles related to the pathologist’s and clinical laboratory’s roles regarding the new oral anticoagulants dabigatran, rivaroxaban, and apixaban.1,2 They describe methods used for measuring plasma levels, potential approaches to reversal, and types of consultations and questions that pathologists may face related to these medications.nnThe first generation of anticoagulants, warfarin and unfractionated heparin, requires continuous monitoring to minimize the risk of bleeding and thrombosis. This is an early example of precision medicine and patient-specific adjustment of levels to optimize therapy. Warfarin is monitored primarily with the prothrombin time (PT)/international normalized ratio on a weekly to monthly basis. Unfractionated heparin was …