Blood Clotting Disorders Linked to Heparin and Vaccines Explained in New Medical Review

The journal The New England Journal of Medicine (NEJM) has posted details of a new review examining platelet-activating anti–platelet factor 4 (anti-PF4) disorders — a group of conditions in which the immune system mistakenly triggers dangerous blood clotting. The review covers heparin-induced thrombocytopenia (HIT), a reaction to the widely used blood-thinning drug heparin, alongside related syndromes including vaccine-induced immune thrombocytopenia and thrombosis (VITT), which came to wider attention during the Covid-19 vaccine rollout.

HIT occurs when the body produces antibodies — proteins made by the immune system — that bind to a complex formed between heparin and a protein called platelet factor 4. Rather than preventing clots, this reaction can paradoxically cause them, sometimes with serious consequences. The NEJM review sets out how clinicians can identify these antibodies, understand how they work, and choose appropriate treatment.

Both conditions are rare.

According to the NHS, heparin is routinely used in hospitals across England — including those across Kent and Medway — to prevent clots after surgery, during kidney dialysis, and in patients with certain heart conditions. Patients receiving heparin who develop a sudden drop in platelet count (the cells that help blood clot normally) should be assessed promptly by their clinical team, the NHS advises.

Anyone concerned about symptoms such as unexpected swelling, redness, or pain in a limb, or unusual bruising, after receiving heparin or a vaccine should contact their GP or call NHS 111 for guidance. In an emergency, call 999.

Key information

• NHS 111 — call 111 for non-emergency health concerns, 24 hours a day, seven days a week
• 999 — call in an emergency, including suspected severe clotting or breathing difficulty
• Your GP — the first point of contact for concerns about a medication reaction or unusual symptoms after treatment