THROMBOSIS AND HAEMOSTASIS
Identifying rare but life- threatening VITT using a highly specific ELISA
Vaccine-induced immune thrombocytopenia and thrombosis has been identified as a rare but life-threatening side effect of the ChAdOx1 nCoV-19 adenoviral vector vaccine, and multiple-site thromboses and arterial events are common. Here, Alex Stephenson-Brown looks at the issues and explains how an enzyme-linked immunosorbent assay from Stago can detect cases of the condition.
As vaccine-induced immune thrombocytopenia and thrombosis (VITT) is a new condition, there is limited evidence available to inform clinical management. Recent research1
by the
UK’s Expert Haematology Panel indicates overall mortality to be as high as 22%, with the greatest risk of death from those presenting with both a low platelet count and an intracranial haemorrhage. Most were previously fit and healthy young people. The National Institute for Health and Care Excellence (NICE) has also adapted its own recent guidelines based on this haematology panel’s findings.2 Fortunately, treatment options are available, with early interventions thought to produce the best outcomes. Vaccine-induced immune
thrombocytopenia and thrombosis is primarily caused by the patient’s blood developing an antibody that cross reacts with platelet factor 4 and activates the platelets. However, this presents in a pathogenically similar way to heparin- induced thrombocytopenia (HIT), which is a common prothrombotic complication of unfractionated heparin (UFH) and low molecular weight heparin (LMWH) therapies. In a vaccinated patient, the symptoms have been seen to develop
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from five to 30 days after the first vaccine dose, further reflecting an immunological pattern like that of HIT. If the patient is not receiving heparin
therapy, a warning sign would be a low platelet count, with low fibrinogen and disproportionally raised D-dimer. For vaccinated patients presenting with these symptoms, additional specialist investigation running an enzyme-linked
immunosorbent assay (ELISA) such as Stago’s Asserachrom HPIA becomes necessary.3
Stago’s Educational Shorts In both HIT and VITT, patient serum is likely to show high-titre antibodies to platelet factor 4 (H-PF4).4–6
Here lies
the dilemma: running a lateral-flow immunoassay that detects anti-heparin- PF4 IgG antibodies will rule out HIT, but it is not appropriate for ruling out or confirming VITT.
Identifying and ruling out VITT is the theme of the first of Stago’s new Educational Shorts series. Collaborating with Chris Reilly-Stitt, the deputy manager of UK NEQAS Coagulation, the video discusses a recent assessment carried out by UK NEQAS into the most effective ways of identifying and excluding VITT, and how best to differentiate it from HIT. The challenge is that patients may first
present with non-specific symptoms such as a headache and feeling generally
Vaccine-induced immune thrombocytopenia and thrombosis is primarily caused by the patient’s blood developing an antibody that cross reacts with platelet factor 4 and activates the platelets.
SEPTEMBER 2021
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