COVID-19 in Canada linked to clotting problems but not TTP
No increase seen in number of cases of blood disorder during pandemic
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The number of cases of the blood disorder thrombotic thrombocytopenic purpura (TTP) did not increase during the pandemic, but COVID-19 was linked to more suspected clotting problems other than TTP, according to a study by Canadian researchers.
That increase in other clotting conditions was particularly noted in middle-aged men, per the research team.
“During the pandemic, the incidence rate of TTP, averaging 2 cases per million people per year, aligned with pre-pandemic trends reported in Canada,” the researchers wrote. Incidence rate is the frequency of new cases of a disease in a population over a specific period of time.
“Unlike TTP, the incidence of suspected non-TTP [blood-clotting diseases] appeared to increase during the pandemic, especially among males,” the team wrote, noting an increase “from 12.7 to 20.3 cases per million people per year.”
The study detailing these findings, titled “The impact of the COVID-19 pandemic on incidence and clinical presentation of thrombotic microangiopathies: data from a laboratory centralizing ADAMTS-13 testing in Quebec,” was published in the Orphanet Journal of Rare Diseases.
Symptoms of TTP are caused by a faulty ADAMTS13 enzyme, which normally prevents blood clots from forming where they aren’t needed. Without an active ADAMTS13, blood clots form in small vessels — known as thrombotic microangiopathy — and block blood flow to organs.
COVID-19 can trigger an excessive immune response and activation of clotting pathways, which may damage the inner lining of small blood vessels. Case reports have highlighted associations between COVID-19 and thrombotic microangiopathy. Meanwhile, other studies have shown that many patients with COVID-19 developed self-reactive antibodies against ADAMTS-13.
Researcher compared cases of TTP before vs. after COVID-19 pandemic
To learn more about the impact of COVID-19, researchers from the Université de Montréal compared the number of patients suspected of having thrombotic microangiopathy in Quebec before and during the pandemic. All patients were tested for ADAMTS-13 as part of the diagnostic workup for TTP.
From 2017 to 2019, before the COVID-19 pandemic, 500 individuals without a family history of TTP were referred to the laboratory for possible thrombotic microangiopathy. Of these patients, 423 were experiencing their first episode. A total of 50 were found to have an underactive ADAMTS-13 enzyme, which confirmed TTP.
Later, from 2020 to 2022, during the COVID-19 pandemic, 683 patients were referred, with 600 of them being first-time cases. Of these patients, 53 were diagnosed with TTP.
According to the researchers, the average number of new cases of TTP “remained steady” in both periods, with about two cases per million people per year.
During the pandemic, women diagnosed with TTP after being referred for possible thrombotic microangiopathy were a median of 10 years younger than before COVID-19 cases began (41.5 vs. 51.5 years). Neurological symptoms were the most common in both periods but tended to be more frequent during the pandemic (61% vs. 41%).
However, the researchers noted that “the observed trend toward increased neurological symptoms during the pandemic should be interpreted with caution, as it may reflect improved data capture rather than a true change in clinical presentation.”
Increase in cases of other blood-clotting conditions mostly involved men
The number of cases of thrombotic microangiopathy other than those caused by TTP increased during the pandemic, the data showed. In men, the largest increase was seen in those ranging in age from 50 to 59, among whom the number of cases climbed from 11.9 to 28.7 per million per year.
Unlike TTP, cases of suspected thrombotic microangiopathy increased in number at the same time that hospitalizations due to COVID-19 also increased. Thrombotic microangiopathy “is a medical emergency that typically requires intensive hospital treatment,” the researchers noted.
A weak connection was found by researchers, with jumps in thrombotic microangiopathy cases appearing about one week after increases in COVID-19 cases. In 17 patients, an association between thrombotic microangiopathy and COVID-19 was suspected, and three of these had TTP. Most of the other cases linked to COVID-19 were in men.
“The incidence of TTP did not change during COVID-19 pandemic,” the researchers concluded. However, the team noted that these findings suggest that “further studies are needed to clarify the relationship between [thrombotic microangiopathy] and COVID-19 in specific population groups.”
