Identifying and treating vaccine-linked blood clots in general practice

Matt Woodley

28/05/2021 3:35:23 PM

Other than age, there are ‘no known risk factors’ associated with developing blood clots with low platelets following an AstraZeneca vaccination, but GPs can still take steps to protect patients.

Red blood cells
ATAGI estimates that TTS occurs in 2.6 cases per 100,000 doses administered to people under 50.

This article was updated on Monday 31 May to include information on theThrombosis and Haemostasis Society of Australia and New Zealand Multidisciplinary VITT Guideline for Doctors.

The most recent Therapeutic Goods Administration (TGA) COVID-19 vaccine weekly safety report has identified another nine cases of thrombosis with thrombocytopenia syndrome (TTS) that are likely linked to the AstraZeneca vaccine.
Based on local data, the Australian Technical Advisory Group on Immunisation (ATAGI) estimates TTS occurs in 2.6 cases per 100,000 doses administered to those under 50, and in 1.6 cases per 100,000 in people aged 50 and over.
But with Australia’s vaccination program continuing to ramp up, especially in the wake of the Victorian outbreak, Australia’s Chief Medical Officer (CMO) Professor Paul Kelly warned doctors that cases of TTS (also known as vaccine-induced immune thrombotic thrombocytopenia [VITT]) are likely to increase.
So how can GPs identify this rare and potentially dangerous – but increasingly treatable – syndrome?
NSW GP Dr Ai-Vee Chua was part of a multidisciplinary group that contributed to the development of consensus guidelines released earlier this month designed to help doctors diagnose and respond to suspected cases of TTS.
She told newsGP that identifying the syndrome can be a challenge because, aside from younger age, there are ‘no known risk factors’ that place individuals at a higher risk of developing TTS following a COVID-19 AstraZeneca vaccination.
‘Many patients are concerned about receiving the vaccine in light of a previous personal or family history of venous or arterial thrombosis,’ she said.
‘But we can confidently reassure them that a past history of deep venous thrombosis, pulmonary embolism, ischaemic heart disease, stroke, or non-immune thrombophilic disorders does not in fact confer an increased risk of developing TTS/VITT post vaccination.
‘This is clear from the case reviews of TTS/VITT that have been conducted both internationally and within Australia.
‘We also know that the mechanism of TTS/VITT is different to that of other thrombotic disorders; it is triggered by the immune system’s response to the vaccine, with platelet factor 4 [PF4] antibodies detected in the majority of cases.’
Australia has now registered 27 confirmed and six probable cases of TTS out of the more than two million AstraZeneca doses that have been administered to date. To put that in perspective, Dr Chua said, the approximate lifetime risk of venous thromboembolism is ‘around 830 per million’.
Of 33 confirmed or suspected cases, 17 have been discharged from hospital and are recovering, four have left hospital but require outpatient medical care, and nine remain in hospital. The TGA is yet to release information on two of the cases, while a 48-year-old woman died after being vaccinated in early April.


Dr Chua says a better understanding of TTS means it is now a ‘very treatable condition’, but added that timely diagnosis and early treatment are ‘key to saving lives’.
‘We GPs play an important role in counselling patients at the time of their AstraZeneca vaccination; patients need to be made aware that if they have severe or unusual symptoms in the 4–30 days after their vaccination, they need to seek prompt medical attention,’ she said.
‘Red flag symptoms include severe, persistent headache that are different to their “usual” headaches and do not settle with regular analgesics, other neurological symptoms, persistent abdominal pain, leg or chest pain, and a petechial rash.
‘And while the incidence of TTS/VITT remains low, we need to maintain an index of suspicion with anyone presenting with severe or unusual symptoms in that window period of 4–30 days.
‘The guidelines recommend initiating urgent blood tests within four hours, specifically FBC, APTT, PT, fibrinogen and D-dimer. If the platelet count is low and D-dimer levels are above five times the upper limit of normal, then this is highly suspicious for TTS/VITT, and ED referral and further investigations are warranted.’
Given GPs have administered nearly 2.2 million vaccines since the rollout began – the vast majority of which have been AstraZeneca – they are also the most likely to be dealing with complications that arise in the 4–30-day TTS window.

Dr Chua says there are a number of challenges specific to general practice in relation to diagnosing and treating TTS, one of which is balancing the need for prompt investigations without ‘flooding our emergency departments’.
‘Depending on where we are located, what day of the week it is, and the time of day, it may be that we don’t have access to obtaining urgent blood tests in the community setting. In this situation I think it would be prudent to obtain ED or haematology specialist advice as to how best to proceed,’ she said.
‘Another challenge is that early in the development of TTS/VITT, the platelet count may in fact be normal.
‘Quite a number of the cases of TTS/VITT in Australia to date had presented initially with platelets within the normal range, only to have their platelet count drop dramatically just hours later. So if symptoms are persisting and we are unable to pinpoint another diagnosis, it is important to repeat the blood tests and consider referring for imaging.’
Lastly, Dr Chua said GPs will continue to play an important role in the public health response to COVID by helping combat the rise in vaccine hesitancy that has occurred following saturated media coverage of adverse events.
‘We can reassure our patients that overall the COVID-19 AstraZeneca vaccine is a very effective vaccine; it will help protect them from serious illness and death from COVID-19 infection when the next major outbreak of COVID-19 occurs,’ she said.
‘We can help balance the negative media reporting around the AstraZeneca vaccine and TTS/VITT, and let our patients in the 50-plus age group know that their chances of developing TTS/VITT post-vaccination is very low, and that even if they do develop TTS/VITT the condition itself is very treatable.’

More information can be found in the Thrombosis and Haemostasis Society of Australia and New Zealand (THANZ) Multidisciplinary VITT Guideline for Doctors.

Dr Chua is co-hosting a webinar with RACGP NSW&ACT Chair Associate Professor Charlotte Hespe on Monday 31 May, in which haematologists Dr Danny Hsu and Dr Vivien Chen will provide a review of Australian cases of TTS, discuss the newly-released guidelines, and look at how to address patient concerns.

Registrations are now fully subscribed, but
the webinar will be recorded and released online.
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Dr Verity Jane Cooper   29/05/2021 9:27:44 AM

Has any research been done on links to the MTHFR gene? (question from patient)

Dr John Lamb   29/05/2021 3:31:33 PM

The title of the article is a bit misleading. I would have liked to see some information on treatment, and in particular what NOT to do with initial treatment.

Dr Rifaat Roshdy Salama Girgis   30/05/2021 6:46:52 PM

The title of this article is “Identifying and treating vaccine-linked blood clots in general practice“
But you did not mention anything about treatment.
I personally am very interested to know the treatment and the rationale behind choosing that particular treatment in details please.

Dr Soheir Sanki   31/05/2021 10:27:27 AM


Dr Gorgee Karunya Dyer   31/05/2021 9:52:27 PM

Soheir, the guideline is linked in the second last paragraph - "More information can be found in the Thrombosis and Haemostasis Society of Australia and New Zealand (THANZ) Multidisciplinary VITT Guideline for Doctors."

Dr Mark Robert Miller   6/06/2021 9:58:01 PM

The article should perhaps mention the caution in relation to anti-phospholipid syndrome as being a relative contraindication.

The list of conditions for which Comirnaty (Pfizer) is the preferred vaccine has been expanded to also include:
Past history of idiopathic splanchnic (mesenteric, portal, splenic) vein thrombosis
Antiphospholipid syndrome with thrombosis