Blood Clotting Disorder Linked to Heparin and Some Vaccines Explained by Medical Journal

The New England Journal of Medicine (NEJM) posted on X flagging new material on platelet-activating antibodies — proteins that mistakenly target platelet factor 4 (PF4), a substance released by blood cells involved in clotting. According to the journal, these antibodies can trigger two distinct but related disorders: heparin-induced thrombocytopenia (HIT), which occurs in some patients given the blood-thinning drug heparin, and vaccine-induced immune thrombocytopenia and thrombosis (VITT), which was identified in a small number of people after certain COVID-19 vaccines.

Both conditions share the same underlying mechanism. The antibodies activate platelets — the tiny blood cells that help wounds seal — while simultaneously reducing their overall count (thrombocytopenia). The result, according to the NEJM, is a highly prothrombotic state: the body forms clots more readily, even as the platelet count falls.

HIT is the more established of the two. It can develop in patients receiving heparin, a widely used anticoagulant (blood thinner) given during surgery, dialysis, and hospital treatment for clots. VITT came to clinical attention after the rollout of some adenoviral vector COVID-19 vaccines and prompted rapid changes to vaccine guidance in several countries, including the UK.

Both are rare. But they can be severe.

The NHS advises anyone who has recently received heparin or a vaccination and develops symptoms such as severe headache, blurred vision, seizures, chest pain, leg swelling, or tiny blood spots under the skin to seek urgent medical attention. These can be signs of clotting or low platelet counts that need prompt assessment.

If You Have Concerns

• Call NHS 111 if you have symptoms that worry you but are not an emergency
• Call 999 or go to your nearest A&E if you have sudden severe headache, chest pain, difficulty breathing, or stroke symptoms
• Tell any treating clinician about recent heparin use or vaccinations — this helps doctors identify the correct cause quickly