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Australia How are blood clots associated with the AstraZeneca vaccine detected and treated?

22:46  14 june  2021
22:46  14 june  2021 Source:   abc.net.au

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Last week, a 52-year-old woman in New South Wales died of an extremely rare blood clot in her brain.

The blood clotting condition was likely linked to the AstraZeneca COVID-19 vaccine, according to the Therapeutic Goods Administration (TGA).

It was Australia's second post-jab death out of 3.3 million doses of AstraZeneca (which makes up the bulk of the more than 5 million doses of COVID vaccines administered so far).

A total of 48 people have developed blood clots after receiving the AstraZeneca vaccine, with 31 recovering after being in hospital.

The first reports of people experiencing blood clots after receiving the AstraZeneca jab emerged in March this year.

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But experts say we've come a long way in understanding the vaccine-related blood clotting disorder, known as thrombosis with thrombocytopenia syndrome (TTS) — including how to detect it and treat it.

How is blood clotting detected?

The first step in detecting the blood clot issue is getting the timing right, said Vivien Chen, a haematologist specialising in coagulation disorders at the University of Sydney.

"The first entry point is being a patient within the right timeframe after receiving the AstraZeneca vaccine," Dr Chen said.

"The first dose appears to be of particular concern."

TTS symptoms — such as a severe headache that doesn't go away, abdominal pain, blurred vision, and leg pain or swelling — appear four to 30 days after receiving the AstraZeneca vaccine, with a peak time of six to 14 days.

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If you show up to your GP with any of these symptoms following the jab, you will get a blood test known as a platelet count.

Platelets, also known as thrombocytes, are fragments of cells that originate in the bone marrow.

They play a key role in healthy blood clotting, such as preventing excessive bleeding when cuts and scrapes happen.

Normal platelet counts fall between 150,000 to 450,000 per microlitre of blood.

But a platelet count lower than 150,000 results in a condition called thrombocytopenia.

The condition usually results in excessive bleeding, but when it occurs after vaccination, abnormal clotting can happen, though rarely.

This is because in a small number of people, the immune system triggers antibodies that not only recognise COVID-19 proteins, but also platelets.

These antibodies can activate the platelets, causing them to cluster together and go into blood-clotting mode.

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"The consequences of this is the platelets are getting used up in the blood clot and their count drops," Dr Chen said.

Are there any other tests?

If the platelet count is low, the next thing clinicians look for in blood samples is the presence of protein fragments called D-dimers.

These proteins are produced by the body to break down blood clots.

"It basically measures the level of clotting in your body because it's a byproduct of the haemostatic process," said Jim Tiao, a molecular biologist specialising in blood disorders at Murdoch University.

If D-dimers are five times higher in number than normal levels, then it can be a sign of TTS , Dr Tiao said.

Once clinicians have detected a low platelet count and high D-dimer levels, they can go on to see if the blood contains antibodies that target a protein called platelet factor 4, or PF4.

In the lab, clinicians test whether the PF4 antibodies from the patient's blood can activate platelets in blood taken from a donor.

"If they do, that's strong evidence that there is an antibody from the patient that is activating platelets and causing this syndrome," Dr Chen said.

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How quickly can TTS be detected?

Blood tests can detect vaccine-related clots as soon as symptoms appear — whether it's four days after vaccination or 20 — but not earlier than that, said Jose Perdomo, a haemotologist at the University of New South Wales.

"In most cases, [antibodies] can only be found after people feel unwell and present at hospital," Dr Perdomo said.

"It won't be detectable before that."

If patients go to the emergency department of a metropolitan hospital with TTS symptoms, they can receive results from blood screening tests within just an hour, though wait times may be longer in regional hospitals, Dr Chen said.

Once platelet and D-dimer levels from initial tests are confirmed, patients can move straight into treatment while they wait for the results of their PF4 antibody test.

What does treatment involve?

There are two different types of treatment that work together to tackle TTS.

First, patients are put on a blood-thinning medication to slow down the formation of blood clots.

Many widely-used anticoagulants, such as fondaparinux, work well to treat TTS, Dr Chen said.

The only exception is heparin — an anti-blood clot drug that is commonly used to treat heart conditions.

"It can make things work for a small number of TTS patients," she said.

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"Luckily we have a lot of really good non-heparin medications available."

To calm the immune system down, patients also receive a large injection of immunoglobulins — proteins that are a part of the body's defence system.

"This essentially swamps the antibody system, so that vaccine-induced antibodies can't activate the platelets," Dr Chen said.

How long does it take to work?

Blood-thinners and a dose of immunoglobulins can help return platelet counts to normal levels within just a couple of days, Dr Chen said.

"In more severe cases, it can take longer but it's a rapid response to commencement of new therapy," she said.

Dr Chen also said these interventions are safe to use even if the blood clot turns out to be unrelated to the vaccine.

"It's unlikely to cause a large amount of harm to somebody without TTS."

What should I do if symptoms appear?

While the risk of getting a blood clot from the AstraZeneca vaccine is very low, it's important to be aware of the symptoms of TTS and to take action as soon as they appear, Dr Chen said.

If you have a headache that doesn't go away after taking over-the-counter painkillers, it's worth a visit to the GP.

But if more severe symptoms appear — such as numbness, difficulties with speech, or passing blood through bowel movements — it's best to go straight to the emergency department.

"Be aware, but not afraid," Dr Chen said.

"If you happen to be one of those rare individuals that get side effects, then you have the opportunity to access treatment very quickly."

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