Heparin-induced thrombocytopenia: pathophysiology, diagnosis and treatment

Clinical guidance for unfractionated heparin dosing and monitoring in critically ill patients

INTRODUCTION

Unfractionated heparin is a widely used anticoagulant in critically ill patients. It has a well-established safety profile and remains an attractive option for clinicians due to its short half-life and reversibility. Heparin has a unique pharmacokinetic profile, which contributes to significant inter-patient and intra-patient variability in effect. The variability in anticoagulant effect combined with heparin's short half-life mean close monitoring is required for clinical efficacy and preventing adverse effects. To optimize heparin use in critically ill patients effective monitoring assays and dose adjustment strategies are needed.

AREAS COVERED

This paper explores the use of heparin as an anticoagulant and optimal approaches to monitoring in critically ill patients.

EXPERT OPINION

Conventional monitoring assays for heparin dosing have significant limitations. Emerging data appears to favor using anti-Xa assay monitoring for heparin anticoagulation which many centers have successfully adopted as the standard. The anti-Xa assay appears have important benefits relative to the aPTT for heparin monitoring in critically ill patients, and should be considered for broader use.

Accuracy of Diagnosing Heparin-Induced Thrombocytopenia

Importance

Heparin-induced thrombocytopenia (HIT) is a life-threatening condition that requires urgent diagnostic clarification. However, knowledge of the diagnostic utility of the recommended diagnostic tests is limited in clinical practice.

Objective

To evaluate the current diagnostic practice for managing the suspicion of HIT.

Design, Setting, and Participants

This prospective diagnostic study was conducted from January 2018 to May 2021 among consecutive patients with suspected HIT from 11 study centers in Switzerland, Germany, and the United States. Detailed clinical data and laboratory information were recorded. Platelet factor 4/heparin antibodies were quantified using an automated chemiluminescent immunoassay (CLIA). A washed-platelet heparin-induced platelet activation (HIPA) test was used as a reference standard to define HIT.

Exposures

Suspicion of HIT.

Main Outcomes and Measures

The primary outcome was the diagnostic accuracy of the 4Ts score, the CLIA, and the recommended algorithm serially combining both tests.

Results

Of 1448 patients included between 2018 and 2021, 1318 were available for the current analysis (median [IQR] age, 67 [57-75] years; 849 [64.6%] male). HIPA was positive in 111 patients (prevalence, 8.4%). The most frequent setting was intensive care unit (487 [37.0%]) or cardiovascular surgery (434 [33.0%]). The 4Ts score was low risk in 625 patients (46.8%). By 2 × 2 table, the numbers of patients with false-negative results were 10 (9.0%; 4Ts score), 5 (4.5%; CLIA), and 15 (13.5%; recommended diagnostic algorithm). The numbers of patients with false-positive results were 592 (49.0%; 4Ts score), 73 (6.0%; CLIA), and 50 (4.1%; recommended diagnostic algorithm), respectively.

Conclusions and Relevance

In this diagnostic study of patients suspected of having HIT, when the recommended diagnostic algorithm was used in clinical practice, antibody testing was required in half the patients. A substantial number of patients were, however, still misclassified, which could lead to delayed diagnosis or overtreatment. Development of improved diagnostic algorithms for HIT diagnosis should be pursued.

The Crosstalk between Nephropathy and Coagulation Disorder: Pathogenesis, Treatment, and Dilemmas

ABSTRACT

The interaction between the kidney and the coagulation system greatly affects each other because of the abundant vessel distribution and blood perfusion in the kidney. Clinically, the risks of complicated thrombosis and bleeding have become important concerns in the treatment of nephropathies, especially nephrotic syndrome, CKD, ESKD, and patients with nephropathy undergoing RRTs. Adverse effects of anticoagulant or procoagulant therapies in patients with nephropathy, especially anticoagulation-related nephropathy, heparin-induced thrombocytopenia, and bleeding, seriously worsen the prognosis of patients, which have become challenges for clinicians. Over the decades, the interaction between the kidney and the coagulation system has been widely studied. However, the effects of the kidney on the coagulation system have not been systematically investigated. Although some coagulation-related proteins and signaling pathways have been shown to improve coagulation abnormalities while avoiding additional kidney damage in certain kidney diseases, their potential as anticoagulation targets in nephropathy requires further investigation. Here, we review the progression of research on the crosstalk between the coagulation system and kidney diseases and systematically analyze the significance and shortcomings of previous studies to provide new sight into future research. In addition, we highlight the status of clinical treatment for coagulation disorder and nephropathy caused by each other, indicating guidance for the formulation of therapeutic strategies or drug development.

A Functional Assay for the Determination of Heparin-Induced Thrombocytopenia via Flow Cytometry

Heparin-induced thrombocytopenia (HIT) is a life-threatening complication of heparin therapy (both unfractionated heparin and low-molecular-weight heparin). In our study, we examined a group of 122 patients with suspected HIT. The samples of all patients were analyzed in the first step using an immunoassay (ID-PaGIA Heparin/PF4, Hemos1L-Acustar HIT IgG, ZYMUTEST HIA Monostrip IgG) to detect the presence of antibodies against heparin-PF4 complexes (platelet factor 4). When the immunoassay was positive, the sample was subsequently analyzed for HIT with a functional flow cytometry assay, the HITAlert kit, the purpose of which was to demonstrate the ability of the antibodies present to activate platelets. A diagnosis of HIT can be made only after a positive functional test result. In this article, we present an overview of our practical experience with the use of the new functional method of analysis, HIT, with flow cytometry. In this work, we compared the mutual sensitivity of two functional tests, SRA and the flow cytometry HITAlert kit, in patients perceived as being at risk for HIT. This work aims to delineate the principle, procedure, advantages, pitfalls, and possibilities of the application of the functional test HITAlert using flow cytometry.

Glucocorticoid-induced thrombotic microangiopathy in paroxysmal nocturnal hemoglobinuria: A case report and review of literature

BACKGROUND

Thrombotic microangiopathy (TMA) is a group of disorders that converge on excessive platelet aggregation in the microvasculature, leading to consumptive thrombocytopenia, microangiopathic hemolysis and ischemic end-organ dysfunction. In predisposed patients, TMA can be triggered by many environmental factors. Glucocorticoids (GCs) can compromise the vascular endothelium. However, GC-associated TMA has rarely been reported, which may be due to the lack of awareness of clinicians. Given the high frequency of thrombocytopenia during GC treatment, particular attention should be given to this potentially fatal complication.

CASE SUMMARY

An elderly Chinese man had a 12-year history of aplastic anemia (AA) and a 3-year history of paroxysmal nocturnal hemoglobinuria (PNH). Three months earlier, methylprednisolone treatment was initiated at 8 mg/d and increased to 20 mg/d to alleviate complement-mediated hemolysis. Following GC treatment, his platelet counts and hemoglobin levels rapidly decreased. After admission to our hospital, the dose of methylprednisolone was increased to 60 mg/d in an attempt to enhance the suppressive effect. However, increasing the GC dose did not alleviate hemolysis, and his cytopenia worsened. Morphological evaluation of the marrow smears revealed increased cellularity with an increased percentage of erythroid progenitors without evident dysplasia. Cluster of differentiation (CD)55 and CD59 expression was significantly decreased on erythrocytes and granulocytes. In the following days, platelet transfusion was required due to severe thrombocytopenia. Observation of platelet transfusion refractoriness indicated that the exacerbated cytopenia may have been caused by the development of TMA due to GC treatment because the transfused platelet concentrates had no defects in glycosylphosphatidylinositol-anchored proteins. We examined blood smears and found a small number of schistocytes, dacryocytes, acanthocytes and target cells. Discontinuation of GC treatment resulted in rapidly increased platelet counts and steady increases in hemoglobin levels. The patient’s platelet counts and hemoglobin levels returned to the levels prior to GC treatment 4 weeks after GC discontinuation.

CONCLUSION

GCs can drive TMA episodes. When thrombocytopenia occurs during GC treatment, TMA should be considered, and GCs should be discontinued.

Comparison of bivalirudin versus heparin in adult extracorporeal membrane oxygenation anticoagulant therapy: A retrospective case-control study

INTRODUCTION

There were controversial opinions on the use of bivalirudin versus heparin for anticoagulant therapy in extracorporeal membrane oxygenation. The aim of our present study is to evaluate the efficacy and safety of bivalirudin versus heparin for the maintenance of systemic anticoagulation during adult veno-venous extracorporeal membrane oxygenation (V-V ECMO).

METHODS

Adult patients who received V-V ECMO support in our center between February 2018and February 2022 were retrospectively recruited. We analyzed their ECMO support time, platelet count, coagulation indicators, blood product infusion volume, the incidence of thrombosis and bleeding, probability of successful weaning of ECMO, and in-hospital mortality.

RESULTS

A total of 58 patients received V-V ECMO support. Thirty-four patients were finally included according to the exclusion and inclusion criteria, 14 and 20 accepted bivalirudin and heparin for anticoagulant therapy, respectively. The Minimum platelet value (98.50 × 10⁹/L (85.50, 123.75) vs 49.50 × 10⁹/L (31.25, 83.00), p = 0.002) and mean platelet value (149.90 × 10⁹/L (127.40, 164.80) vs 74.55 × 10⁹/L (62.45, 131.60), p = 0.03) and the ratio of successful weaning of ECMO (92.8% vs 60.0%, p = 0.033) in bivalirudin group were significantly higher than those in heparin group. The red blood cell infusion volume (7.00 U (3.00, 13.25) vs 13.75 U (7.25, 22.63), p = 0.039), platelet infusion volume (0.00 mL (0.00, 75.00) vs 300 mL (0.00, 825.00), p = 0.027), and the incidence of major bleeding (0.00% vs 30%, p = 0.024) in bivalirudin group were significantly lower than those in heparin group.

CONCLUSIONS

In V-V ECMO-supported adult patients, systemic anticoagulation with bivalirudin has achieved the same anticoagulation targets as heparin with less frequency of major bleeding events and lower requirement for blood products without significantly increased risk of thrombosis. Bivalirudin most likely is a safe and effective anticoagulation method for adult patients supported by V-V ECMO.

Heparin-Induced Thrombotic Thrombocytopenia (HITT) and Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT): Similar but Different

Heparin-induced thrombocytopenia (HIT) represents an autoimmune process whereby antibodies are formed against heparin in complex with platelet factor 4 (PF4) after heparin administration. These antibodies can be detected by a variety of immunological assays, including ELISA (enzyme-linked immunosorbent assay) and by chemiluminescence on the AcuStar instrument. However, pathological HIT antibodies are those that activate platelets in a platelet activation assay and cause thrombosis in vivo. We would tend to call this condition heparin-induced thrombotic thrombocytopenia (HITT), although some workers instead use the truncated abbreviation HIT. Vaccine-induced (immune) thrombotic thrombocytopenia (VITT) instead reflects an autoimmune process whereby antibodies are formed against PF4 after administration of a vaccine, most notably adenovirus-based vaccines directed against COVID-19 (coronavirus disease 2019). Although both VITT and HITT reflect similar pathological processes, they have different origins and are detected in different ways. Most notable is that anti-PF4 antibodies in VITT can only be detected immunologically by ELISA assays, tending to be negative in rapid assays such as that using the AcuStar. Moreover, functional platelet activation assays otherwise used for HITT may need to be modified to detect platelet activation in VITT.

How often are parenteral anticoagulants administered by parents?

Parenteral anticoagulants are a class of anticoagulants that need to be administered non-orally, usually by injection or infusion. There are a variety of such agents, but heparin reflects the most frequently used. Being alerted to an error in a prior publication in which the word "parenteral" was inadvertently replaced by the word "parental," it became clear that even experienced authors make such errors, which could then remain undetected by reviewers and editors, thus leading to failure in correction of same before publication. Given this is likely to be a somewhat ongoing error, we undertook a PubMed search of the literature to identify that "parentally administered" anticoagulants, as well as "parental" administration of other compounds, seems to be evident throughout the literature. We hope this report acts to raise awareness and help avoid similar errors in the future.

Autoimmune Diseases Affecting Hemostasis: A Narrative Review

Hemostasis reflects a homeostatic mechanism that aims to balance out pro-coagulant and anti-coagulant forces to maintain blood flow within the circulation. Simplistically, a relative excess of procoagulant forces can lead to thrombosis, and a relative excess of anticoagulant forces can lead to bleeding. There are a wide variety of congenital disorders associated with bleeding or thrombosis. In addition, there exist a vast array of autoimmune diseases that can also lead to either bleeding or thrombosis. For example, autoantibodies generated against clotting factors can lead to bleeding, of which acquired hemophilia A is the most common. As another example, autoimmune-mediated antibodies against phospholipids can generate a prothrombotic milieu in a condition known as antiphospholipid (antibody) syndrome (APS). Moreover, there exist various autoimmunity promoting environments that can lead to a variety of antibodies that affect hemostasis. Coronavirus disease 2019 (COVID-19) represents perhaps the contemporary example of such a state, with potential development of a kaleidoscope of such antibodies that primarily drive thrombosis, but may also lead to bleeding on rarer occasions. We provide here a narrative review to discuss the interaction between various autoimmune diseases and hemostasis.

A case of severe COVID-19 with pulmonary thromboembolism related to heparin-induced thrombocytopenia during prophylactic anticoagulation therapy

A 53-year-old male Japanese patient with COVID-19 was admitted to our hospital after his respiratory condition worsened on day 9 of the disease. With the diagnosis of severe COVID-19, treatment with remdesivir, dexamethasone, and unfractionated heparin was started for the prevention of thrombosis. Although the patient's respiratory status data improved after treatment, severe respiratory failure persisted. Thrombocytopenia and D-dimer elevation were observed on day 8 after heparin therapy initiation. Heparin-induced thrombocytopenia (HIT) antibody measured by immunological assay was positive, and contrast computed tomography showed pulmonary artery thrombus. The patient was diagnosed with HIT because the pre-test probability score (4Ts score) for HIT was 7 points. Heparin was changed to apixaban, a direct oral anticoagulant, which resulted in a reduction of the pulmonary thrombus and improvement of the respiratory failure. In patients with COVID-19, anticoagulant therapy with heparin requires careful monitoring of thrombocytopenia and elevated D-dimer as possible complications related to HIT. (151/250 words).

2021 ELSO Adult and Pediatric Anticoagulation Guidelines

DISCLAIMER

These guidelines for adult and pediatric anticoagulation for extracorporeal membrane oxygenation are intended for educational use to build the knowledge of physicians and other health professionals in assessing the conditions and managing the treatment of patients undergoing ECLS / ECMO and describe what are believed to be useful and safe practice for extracorporeal life support (ECLS, ECMO) but these are not necessarily consensus recommendations. The aim of clinical guidelines are to help clinicians to make informed decisions about their patients. However, adherence to a guideline does not guarantee a successful outcome. Ultimately, healthcare professionals must make their own treatment decisions about care on a case-by-case basis, after consultation with their patients, using their clinical judgment, knowledge and expertise. These guidelines do not take the place of physicians' and other health professionals' judgment in diagnosing and treatment of particular patients. These guidelines are not intended to and should not be interpreted as setting a standard of care or be deemed inclusive of all proper methods of care nor exclusive of other methods of care reasonably directed to obtaining the same results. The ultimate judgment must be made by the physician and other health professionals and the patient in light of all the circumstances presented by the individual patient, and the known variability and biological behavior of the clinical condition. These guidelines reflect the data at the time the guidelines were prepared; the results of subsequent studies or other information may cause revisions to the recommendations in these guidelines to be prudent to reflect new data, but ELSO is under no obligation to provide updates. In no event will ELSO be liable for any decision made or action taken in reliance upon the information provided through these guidelines.

Laboratory testing for platelet factor 4 antibodies: differential utility for diagnosis/exclusion of heparin induced thrombocytopenia versus suspected vaccine induced thrombotic thrombocytopenia

Platelet factor 4 (PF4), a protein stored in the alpha-granules of platelets and released upon activation, forms cationic tetramers that bind with various polymeric anions, including heparin. Some individuals develop antibodies against PF4 in complex with heparin (PF4/H), which potentially lead to the onset of heparin induced thrombocytopenia (HIT). In some patients, this may cause activation and aggregation of platelets, promoting pathological thrombosis, in a process called heparin induced thrombocytopenia with thrombosis ('HITT'). Laboratories can assess for the presence of these antibodies using many PF4 antibody tests, including by enzyme linked immunosorbent assay (ELISA), latex immunoassay (LIA), chemiluminescence immunoassay (CLIA) and even rapid nanoparticle based lateral flow immunoassays. All these assays can identify such antibodies with high sensitivity, but methods may have variable specificity. For example, several studies have shown CLIA assays to have higher specificity to HITT than ELISA assays. Very recently, a new 'HITT-like' syndrome has been described in some individuals receiving adenovirus based COVID-19 (coronavirus disease 2019) vaccines. This condition has been given several names, including vaccine induced thrombotic thrombocytopenia (VITT) and thrombosis with thrombocytopenia syndrome (TTS), and also involves a mechanism mediated by antibodies formed against PF4. These antibodies can also be detected by PF4 antibody tests, but detection sensitivity appears to favour ELISA assays, with most other tests (including CLIA and LIA) not generally capable of detecting such antibodies. Additional functional assays assessing for PF4 mediated platelet activation may also be performed. The current review is focussed on laboratory testing for PF4 antibodies, in particular to distinguishing patterns in HITT versus VITT.

Review and evolution of guidelines for diagnosis of COVID-19 vaccine induced thrombotic thrombocytopenia (VITT)

Coronavirus disease 2019 (COVID-19) is a life-threatening infectious disease caused by Severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2). In response to the still ongoing pandemic outbreak, a number of COVID-19 vaccines have been quickly developed and deployed. Although minor adverse events, either local (e.g., soreness, itch, redness) or systematic (fever, malaise, headache, etc.), are not uncommon following any COVID-19 vaccination, one rare vaccine-associated event can cause fatal consequences due to development of antibodies against platelet factor 4 (PF4), which trigger platelet activation, aggregation, and possible resultant thrombosis, often at unusual vascular sites. Termed thrombosis with thrombocytopenia syndrome (TTS) by reporting government agencies, the term vaccine-induced (immune) thrombotic thrombocytopenia (VITT) is more widely adopted by workers in the field. In response to increasing reports of VITT, several expert groups have formulated guidelines for diagnosis and/or management of VITT. Herein, we review some key guidelines related to diagnosis of VITT, and also provide some commentary on their development and evolution.