Why Is Aspirin Stopped in ET With Very High Platelets?

It can be incredibly confusing to have Essential Thrombocythemia (ET), a condition known for causing blood clots, and be told to stop taking aspirin. The reason is a complication called Acquired von Willebrand Syndrome (AVWS). When your platelet count gets extremely high, your body’s normal clotting proteins can become depleted. This doesn’t completely remove your risk of blood clots, but it introduces a new, serious risk of bleeding ^[1]. Aspirin is an antiplatelet medicine that makes platelets less sticky; taking it when you already have AVWS can tip the balance and dangerously worsen your bleeding risk ^[2][3].

How High Platelets Cause AVWS

Think of von Willebrand factor (VWF) as the “glue” that helps platelets stick together to form a protective plug when you are bleeding. The most effective pieces of this glue are large structures called high-molecular-weight multimers.

When your platelet count becomes excessively high (a state called extreme thrombocytosis), the sheer number of platelets circulating in your bloodstream causes problems. These excessive platelets latch onto the VWF protein, causing the crucial high-molecular-weight multimers to break down and be rapidly consumed ^[1][4].

Because your body uses up its best clotting glue faster than it can replace it, the initial formation of a platelet plug becomes less effective ^[5]. This creates a bleeding disorder that mimics an inherited condition called von Willebrand disease. Because it is caused by high platelets rather than inherited genetics, it is called an acquired syndrome ^[1][6].

Balancing Clotting and Bleeding Risks

Your hematologist manages ET by constantly balancing your risk of thrombosis (clotting) against your risk of bleeding. Platelet counts are commonly used as triggers to evaluate these risks, though they are guidelines rather than absolute rules:

• Routine ET Management: Many ET patients take low-dose aspirin to reduce the risk of heart attacks, strokes, and blood clots. However, this is always an individualized decision based on age, cardiovascular risk, prior clots, and specific genetic mutations ^[7].
• Approaching 1,000 × 10^9/L (about 1 million/µL): Guidelines recommend that doctors screen you for AVWS before starting or continuing aspirin ^[2][8]. Taking antiplatelet medicines when your von Willebrand factor is depleted can severely worsen bleeding ^[3].
• Approaching 1,500 × 10^9/L (about 1.5 million/µL): The risk of AVWS-related bleeding becomes much higher, and doctors often consider initiating medications to actively lower the platelet count ^[9].

These thresholds do not mean you will definitively bleed or clot at a certain number. Some patients experience AVWS with platelet counts below 1 million, while others with extreme counts do not develop bleeding issues ^[6][5]. Your specific mutation also matters; for example, in certain low-risk patients, having a CALR mutation is associated with a higher bleeding risk when taking aspirin ^[7][10].

How AVWS is Tested and Treated

If your platelet count is very high, your doctor will likely run specialized blood tests ^[11][12]. You might hear them discuss:

• VWF Antigen: Measures the total amount of VWF protein in your blood.
• VWF Activity: Measures how well the VWF “glue” is actually working.
• Multimer Analysis: Checks if the large, most effective pieces of VWF are missing.

If you have AVWS, the primary long-term treatment focuses on the root cause by lowering your platelet count. Cytoreductive therapies (medicines that reduce the excessive production of blood cells, like hydroxyurea or pegylated interferon) lower your platelet count and stop the rapid consumption of your VWF glue ^[4][13]. For severe, active bleeding or before an urgent surgery, specialists may use emergency hemostatic treatments like desmopressin, VWF-containing concentrates, or rapid mechanical platelet removal (plateletpheresis) ^[14][15].

Once your platelet counts are lowered by cytoreductive medication, your doctor will repeat VWF tests to confirm if your levels have recovered. Never stop or restart aspirin on your own—especially if it was prescribed for a previous heart attack, stroke, or stent—until your doctor confirms it is safe ^[4]. Also, avoid other medications that increase bleeding risk, such as NSAIDs (ibuprofen, naproxen) or certain supplements, unless explicitly approved by your care team.

When to Seek Emergency Care

Because you are managing both bleeding and clotting risks simultaneously, seek immediate emergency medical care (do not wait for a routine appointment) if you experience:

• Signs of severe bleeding: Bleeding that will not stop, black or bloody stools, vomiting or coughing up blood, blood in your urine, unusually heavy menstrual bleeding, severe or sudden headache, or fainting.
• Signs of a blood clot: Chest pain, sudden shortness of breath, sudden weakness or numbness (especially on one side of the face or body), difficulty speaking, or a new, painful, swollen leg.