An update on heparin-induced thrombocytopenia: diagnosis and management

Breast cancer cell-based ELISA: a potential material for better detection of heparin-induced thrombocytopenia antibodies

Heparin-induced thrombocytopenia (HIT) is caused by newly formed platelet-activating antibodies against complexes formed between platelet factor 4 (PF4) and heparin (H). HIT can result in life-threatening complications; thus, early detection of HIT antibodies is crucial for the treatment of the disease. The enzyme-linked immune absorbance assay (ELISA) for the identification of HIT antibodies is widely used in many laboratories, but in general, this test provides only ∼50% accuracy while other methods show multiple limitations. Here, we developed a new cell-based ELISA to improve the detection of HIT antibodies. Instead of immobilizing PF4 or PF4/H complexes directly onto a plate as in the standard ELISA, we added the complexes on breast cancer cells, i.e., cell line MDA-MB-231, and applied the same protocol for antibody detection. Using confocal laser scanning microscopy and flow cytometry for the characterization of bound complexes, we identified two types of HIT-mimicked antibodies (KKO and 1E12), which were able to differentiate from the non-HIT antibody (RTO). PF4-treated MDA-MB-231 cells allowed binding of HIT-mimicked antibodies better than PF4/H complexes. With human sera, the cell-based ELISA allowed better differentiation of clinically relevant from non-clinically relevant HIT antibodies as compared with the standard ELISA. Our findings provide a potential approach that contributes to the development of better assays for the detection of HIT antibodies.

Development and validation of a liquid chromatography/tandem mass spectrometry method for the simultaneous quantification of serotonin and thromboxane B2 from activated platelets

INTRODUCTION

Availability of a rapid and reliable platelet activation assay avoiding limitations of current techniques would be valuable to diagnose heparin-induced thrombocytopenia and platelet secretion disorders.

OBJECTIVES

The first aim was to develop and validate an ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method to quantify in a single run TxB2 synthesized and serotonin released from platelets. The second aim was to use our method in association with light transmission aggregometry (LTA) to select good platelet responders for the diagnosis of HIT.

METHODS

Electrospray ionization and chromatographic separation were optimized for the simultaneous dosage of serotonin and TxB2. The method was validated according to the European Medicines Agency (EMA) guideline for bioanalytical method validation. LTA was performed with monoclonal anti-CD9 (clone ALB6) as platelet activator to select good responders.

RESULTS

Detection was performed using a tandem mass spectrometer with alternated positive and negative electrospray ionization. The total run time was 6 minutes. The method was validated for calibration curves, precision, accuracy, lower limit of quantification, carry-over, selectivity, and matrix effect. Platelet response to ALB6 was highly variable among donors.

CONCLUSION

We developed and validated a UHPLC-MS/MS method for the simultaneous quantification of TxB2 and serotonin.

Heparin-Induced Thrombocytopenia in the Critically Ill Patient

Heparin-induced thrombocytopenia (HIT) is associated with clinically significant morbidity and mortality. Patients who are critically ill are commonly thrombocytopenic and exposed to heparin. Although HIT should be considered, it is not usually the cause of thrombocytopenia in the medical-surgical ICU population. A systematic approach to the patient who is critically ill who has thrombocytopenia according to clinical features, complemented by appropriate laboratory confirmation, should lead to a reduction in inappropriate laboratory testing and reduce the use of more expensive and less reliable anticoagulants. If the patient is deemed as being at intermediate or high risk for HIT or if HIT is confirmed by means of the serotonin-release assay, heparin should be stopped, heparin-bonded catheters should be removed, and a direct antithrombin or fondaparinux should be initiated to reduce the risk of thrombosis. Warfarin is absolutely contraindicated in the acute phase of HIT; if administered, its effects must be reversed by using vitamin K.

Functional Assays in the Diagnosis of Heparin-Induced Thrombocytopenia: A Review

A rapid and accurate diagnosis in patients with suspected heparin-induced thrombocytopenia (HIT) is essential for patient management but remains challenging. Current HIT diagnosis ideally relies on a combination of clinical information, immunoassay and functional assay results. Platelet activation assays or functional assays detect HIT antibodies that are more clinically significant. Several functional assays have been developed and evaluated in the literature. They differ in the activation endpoint studied; the technique or technology used; the platelet donor selection; the platelet suspension (washed platelets, platelet rich plasma or whole blood); the patient sample (serum or plasma); and the heparin used (type and concentrations). Inconsistencies in controls performed and associated results interpretation are common. Thresholds and performances are determined differently among papers. Functional assays suffer from interlaboratory variability. This lack of standardization limits the evaluation and the accessibility of functional assays in laboratories. In the present article, we review all the current activation endpoints, techniques and methodologies of functional assays developed for HIT diagnosis.