Hematologist
CION Cancer Clinics
Recurrent clots despite treatment: what to do and why it happens | CION Cancer Clinics
A new clot while you are on a blood thinner is uncommon, and it needs a hospital check the same day. Keep taking the medicine as prescribed. The usual reasons are missed doses, a medicine clash or a blood level out of range, and sometimes a hidden cause. Your team first confirms the clot is new, then finds the reason before changing anything. If you are breathless, call 108. At CION Cancer Clinics, our haematologist cares for anaemia, bleeding, clotting and inherited blood disorders, with ArogyaSri, CGHS and cashless insurance accepted.
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Medically reviewed by Dr. Basudev PokhrelConsultant Haematologist · last reviewed September 2026, next review due September 2027
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On this page
- Why would a clot come back while you are on a blood thinner?
- What are the usual reasons a blood thinner seems to fail?
- What will the doctors check?
- What do the words on your scan and blood report mean?
- What do families often assume when a clot comes back?
- What might change in your treatment, and who decides?
- Common questions about clots on blood thinners
!
Do this first
If you are on a blood thinner and a leg becomes newly swollen, painful or warm, get checked at a hospital the same day. If you have sudden breathlessness, chest pain or cough up blood, call 108 or go to the nearest emergency department now. Tell them which blood thinner you take and when you took the last dose. Do not stop it, double it or switch it on your own.
The short answer
Why would a clot come back while you are on a blood thinner?
A new clot on a blood thinner is uncommon, and it usually has a reason that can be found. Often it is missed or late doses, a medicine clash, or a blood level that has drifted. Sometimes the cause is hidden, such as a cancer not yet found or antiphospholipid syndrome, a condition that makes the blood clot too easily.
Is it really a new clot?
This is the first question your team asks. An old clot can take a long time to clear, and some of it may never fully go. A leg that stays swollen or aches after a DVT, short for deep vein thrombosis, may be damage from the first clot. Doctors call that post-thrombotic syndrome. A new scan compared with the old one is often the only way to tell.
Why it matters to know
If the clot is new, the treatment plan needs changing. If it is old, a change of medicine could add bleeding risk and help nothing. That is why your old scan reports are so valuable at this appointment.
Only your treating doctor can decide whether a clot is new and what to change. This page explains the thinking, not your answer.Not sure whether this applies to you?
Ask an oncologistTroubleshooting
What are the usual reasons a blood thinner seems to fail?
Most have a fix once they are found. Some need tests to uncover.
Doses missed or taken late
Newer tablet blood thinners leave the body quickly. A few skipped or late doses can leave the blood unprotected. Be honest with your doctor about gaps. It is common and changes the plan.
A level out of range
On warfarin, the INR blood test shows how thin the blood is. If it has stayed low, protection was weaker than it looked. Food changes and illness can shift it.
A medicine or herbal clash
Some medicines lower how well a blood thinner works.
Ask about
- Some fits and TB medicines
- Some antibiotics and antifungals
- Herbal or ayurvedic products
A cause still active
Cancer, antiphospholipid syndrome and some rare blood disorders can drive clots through ordinary treatment.
Also relevant
- Kidney or liver changes
- Large weight change
- Stomach surgery that affects absorption
The work-up
What will the doctors check?
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Confirm the clot is new
A Doppler ultrasound of the leg, or a CT scan of the chest if a lung clot is suspected, compared with your earlier scans.
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Go through how you take the medicine
Which blood thinner, what time, with or without food, and any gaps. Bring the strips or the bottle.
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Blood tests
Blood counts, kidney and liver function, and the INR if you take warfarin. Sometimes a drug level test is added.
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Review every other medicine
Including anything from a local pharmacy, herbal products and supplements started recently.
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Look for a hidden cause
Tests for antiphospholipid syndrome, and checks for cancer suited to your age and symptoms. Not everyone needs every test.
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On your report
What do the words on your scan and blood report mean?
- Recurrent VTE
- A new clot in a vein or the lungs after an earlier one. VTE means venous thromboembolism.
- Residual thrombus
- Part of the old clot still visible on the scan. It does not by itself mean a new clot.
- Post-thrombotic syndrome
- Lasting swelling, heaviness or skin changes in a leg after a DVT, caused by damaged vein valves.
- INR
- A blood test for people on warfarin that shows how long the blood takes to clot.
- Antiphospholipid antibodies
- Proteins that make the blood clot too easily. Tests are usually repeated to confirm.
Commonly believed
What do families often assume when a clot comes back?
"The tablet is not working, so we will take two."
Taking extra raises the risk of serious bleeding and may not fix the cause. Any change in dose or medicine must come from the doctor who prescribed it, after the reason is found.
"It failed, so there is no point taking it."
Stopping a blood thinner after a new clot is dangerous. Keep taking it as prescribed until your doctor has seen you and made a new plan.
"My leg is still swollen, so the clot is back."
Not always. Lasting swelling is often damage from the first clot. A sudden change, a new painful area or breathlessness is what needs a same-day check.
"A clot on treatment means it must be cancer."
Cancer is one possible reason, and doctors look for it sensibly. Many people with a repeat clot have a simpler cause, such as missed doses or a medicine clash.
The next step
What might change in your treatment, and who decides?
Your haematologist chooses the next step once the reason is clear. The aim is to protect you from another clot without adding too much bleeding risk.
Options the team may consider
If doses were missed, the answer may be a simpler routine rather than a new medicine. If a clash is found, the other medicine may be changed. Some people are moved from tablets to an injection called low molecular weight heparin, often used in cancer-related clots. For antiphospholipid syndrome, warfarin is usually preferred over the newer tablets.
What a vein filter is, and who it suits
An IVC filter is a small device placed in the large vein in the belly to catch clots. It is kept for people who cannot safely take blood thinners. It does not suit most people with a repeat clot, and it does not stop new clots forming in the leg.
What this page cannot tell you
It cannot tell you whether your clot is new, why it happened, or which medicine is right. At CION, Dr. Basudev Pokhrel reviews repeat clots with your scans, blood reports and medicine list. Bring all three.
Questions we are asked
Common questions about clots on blood thinners
Should I stop my blood thinner if I get a new clot?
No. Keep taking it as prescribed and get seen the same day. Stopping it can let the clot grow or spread to the lungs. Your doctor will decide whether to continue, change the medicine or add something, once they know why the clot happened.
How do I know if it is a new clot or the old one?
You usually cannot tell from the leg alone. A new scan compared with your earlier scan is the reliable way. Sudden new swelling, pain in a new place or breathlessness points towards a new problem and needs checking the same day.
I missed a few tablets last week. Could that be why?
It may be. Newer tablet blood thinners wear off quickly, so gaps matter. Tell your doctor exactly what was missed. There is no blame in it, and it helps them choose the right plan. Do not make up for missed doses by taking extra.
Does a repeat clot mean I have cancer?
Not necessarily. Cancer is one of several possible causes, and your doctor will look for it in a sensible way based on your age and symptoms. Many repeat clots turn out to have a simpler reason, such as doses, a medicine clash or a blood level out of range.
Will I have to take blood thinners for life now?
Some people are advised to continue long term after a repeat clot, especially if the cause cannot be removed. Others are not. The decision weighs your clot risk against your bleeding risk, and it is reviewed over time. Ask your haematologist to explain the balance for you.
Can food or ayurvedic medicine affect my blood thinner?
Yes. On warfarin, large changes in green leafy vegetables can shift the INR. Some herbal and ayurvedic products change how blood thinners work or add bleeding risk. Tell your doctor about everything you take, even if it seems harmless.
What tests will I need?
Usually a scan to confirm the clot, blood counts, kidney and liver tests, and an INR if you take warfarin. Some people need tests for antiphospholipid syndrome or checks for cancer. Your doctor will choose the tests that fit your situation, not a fixed list.
What should I bring to the appointment?
Every scan report from the first clot and this one, recent blood reports, your INR record if you take warfarin, and all your medicines, including herbal products. A written note of any missed doses helps. Bring the family member who helps manage your medicines.
Your Haematologist
Meet CION's haematologist. One specialist for your blood report and your plan.
Dr. Basudev Pokhrel reviews blood counts, transfusion needs and blood disorders, and works with the CION tumour board on blood cancers.
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Sources
- NHS — Deep vein thrombosis (DVT)
- NHLBI — Venous thromboembolism
- American Society of Hematology — Blood clots
- NICE — Venous thromboembolic diseases: diagnosis, management and thrombophilia testing (NG158)
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
How Long to Stay on Blood ThinnersWhat decides the length of treatment after a clotMissed Anticoagulant Dose: What to DoThe most common reason protection slipsAntiphospholipid SyndromeA hidden cause of clots that keep coming backCancer-Associated ThrombosisHow clots are treated when cancer is involvedClotting, Thrombosis and AnticoagulationThe full guide to clots and blood thinners
Talk to us
Had another clot on a blood thinner?
Send us your scan reports, blood reports and medicine list. Our haematology team will review them and help you plan the next step. For breathlessness or chest pain, call 108 first.