Elevated Blood Clot Risk Persists in Some COVID-19 Cases

Medically Reviewed by Expert Board

This page was fact checked by our expert Medical Review Board for accuracy and objectivity. Read more about our editorial policy and review process.

This article was last modified on

More than a year following the emergence of SARS-CoV-2, the virus that causes COVID-19, researchers are starting to gain better understanding of some of the effects, both short- and long-term, the illness can have on the body. One such effect, found commonly amongst COVID-19 patients with illness of varying severity, is elevated blood D-dimer levels.

D-dimer is a protein produced when blood clots form and then break down. Elevated blood D-dimer levels can be a sign of increased blood clotting in the body.

The D-dimer protein fragment is typically undetectable in the blood, or detected at low levels, which increase slightly with age. However, unless the body is actively forming clots and breaking down already formed blood clots, the blood D-dimer level should be below age-specific cutoff limits.

Conversely, elevated D-dimer levels can signify increased blood clotting, which is part of the body’s natural response to inflammation and blood vessel or tissue injury. Increased blood clotting can lead to complications such as deep vein thrombosis (DVT), pulmonary embolism (PE), heart attack, and stroke. Elevated D-dimer levels, as seen in some patients with severe COVID-19, can indicate an elevated risk of blood clots and complications. Undetected and untreated, blood clots can contribute to unfavorable outcomes and have proven to be fatal in some cases of severe COVID-19.

Recently, a group of scientists studied the effects of persistent COVID-19, commonly called Long COVID-19, and its relationship to inflammation and blood clotting. Some patients experience ongoing symptoms such as fatigue, difficulty breathing and lack of endurance, even after the acute illness resolves. The researchers followed 150 COVID‐19 patients who were treated at St James’s Hospital Dublin from May to September 2020 for a median of 80 days after they were first diagnosed. Their report, published in the Journal of Thrombosis and Haemostasis, found that D-dimer levels remained elevated in about 25% of study participants for up to four months following COVID-19 diagnosis. Elevated D-dimer levels were mostly found in those hospitalized with severe disease and patients age 50 or older.

Data continues to be collected as it pertains to elevated D-dimer levels in patients with varying severity of COVID-19. Recommendations currently suggest that D-dimer levels be monitored even after COVID-19 hospital discharge, as it is unknown how long elevated risk of blood clotting persists, and when it resolves. There is also speculation that the potential for increased blood clot risk – similarly to COVID-19 severity – may increase depending on underlying health conditions associated with the patient. Examples of such underlying conditions include but are not limited to cancer, bodily trauma such as fractures or surgery, autoimmune disorders, and heart failure.

Although elevated D-dimer levels have been commonly detected amongst COVID-19 patients, there is no evidence to explain how or why these elevations occur. Also unclear is why these levels are increasingly high in patients with a severe COVID-19 diagnosis, and why elevations persist in some patients. Authors of the study call for more research to gain a better understanding of the effects of Long COVID-19. Determining why D-dimer levels remain elevated may help to understand why some patients suffer from Long COVID-19 and may be informative for how these patients can be effectively managed and treated.

Related Pages


(April 8, 2021) Southall, Jennifer. Elevated D-dimer levels common months after COVID-19 diagnosis. Healio, Hematology/Oncology. Accessed May 1, 2021.  https://www.healio.com/news/hematology-oncology/20210408/elevated-ddimer-levels-common-months-after-covid19-diagnosis

Townsend L, et al. Prolonged elevation of D‐dimer levels in convalescent COVID‐19 patients is independent of the acute phase response. J Thromb Haemost. 2021; doi:10.1111/jth.15267.

(January 29, 2021) COVID-19 and Coagulopathy: Frequently Asked Questions. American Society of Hematology. Accessed May 1, 2021. https://www.hematology.org/covid-19/covid-19-and-coagulopathy