Heparin-Induced Thrombocytopenia: Causes, Risks, and What to Do

When you get heparin-induced thrombocytopenia, a rare but life-threatening immune reaction triggered by heparin, a common blood thinner. Also known as HIT, it doesn’t just lower your platelets—it makes your blood more likely to clot dangerously, even while you’re on a drug meant to prevent clots. This isn’t a simple side effect. It’s a paradox: the medicine meant to protect you from clots suddenly starts causing them.

Most people get heparin after surgery, during dialysis, or for deep vein thrombosis. But if your immune system mistakes heparin as a threat, it starts attacking your platelets. That’s when your platelet count drops—often below 150,000—and your body starts forming clots in veins or arteries. These clots can lead to stroke, heart attack, or limb loss. It’s not rare in high-risk patients: up to 5% of those on unfractionated heparin develop it. The risk is lower with low-molecular-weight heparin, but it still happens.

What makes HIT tricky is that symptoms don’t always show up right away. You might feel fine for days after your last heparin dose, then suddenly develop swelling, pain, or discoloration in your leg. Or you might have no pain at all—just a drop in platelets on a routine blood test. That’s why doctors watch your platelet count closely during and after heparin treatment. If it drops more than 50% from baseline, HIT is suspected. A lab test called the serotonin release assay or anti-PF4 antibody test confirms it.

Once HIT is diagnosed, stopping heparin isn’t enough. You need a different blood thinner—like argatroban or fondaparinux—that won’t trigger the same immune response. Warfarin is dangerous in the early phase because it can cause skin necrosis. And you can’t use any heparin again—not even in toothpaste or heparin-coated catheters. This isn’t something you can ignore or wait out. Delayed treatment increases your risk of death or permanent damage.

People on long-term heparin, those with prior HIT, or those with infections or cancer are at higher risk. Nurses and pharmacists now check for HIT before giving heparin in many hospitals. But if you’re on heparin at home, watch for sudden pain, swelling, or unexplained bruising. Tell your doctor immediately if your platelets drop or you feel off. Your life might depend on catching it early.

The posts below cover real cases, lab patterns, drug alternatives, and how to avoid dangerous mix-ups with other blood thinners. You’ll find what works, what doesn’t, and what doctors wish patients knew before starting heparin.