For most hospitalized patients, red blood cell (RBC) transfusion does not appear to raise the risk for arterial or venous thrombosis, according to research in the American Journal of Hematology.

Several previous studies have found an increased risk for thrombosis in hospitalized patients. However, the current study authors noted that many previous analyses did not account for patient comorbidities or timing of a thrombotic event in relation to the blood transfusion. With 12 to 16 million units of red blood cells transfused each year in the United States, it is important to understand and manage associated risks.

The authors used the National Heart Lung and Blood Institute (NHLBI) Recipient Epidemiology and Donor Evaluation Study III (REDS-III) database to account for timing of a thrombotic event and comorbidities that may increase the risk of thrombosis. In the database, 67,176 inpatient admissions had received at least 1 RBC transfusion. Of those admissions, 2% (12,927 admissions) experienced at least 1 thrombotic event. Of the 2%, 20% (2587 admissions) had a thrombotic event after an RBC transfusion; 68% of admitted patients who had a thrombotic event were never transfused, and 12% had a transfusion after a thrombotic event.

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The study authors evaluated comorbidities and surgery type for the 2587 patients who had thrombosis after RBC transfusion. This group was compared to the admissions whose thrombotic events were not transfusion-related and admissions without a thrombotic event. Vascular, thoracic, and general surgery were the most common types of surgical procedures. Hypertension, diabetes with complications, arrhythmias, and pulmonary disease were the most frequent comorbidities for evaluated admissions.

Surgical procedures and common comorbidities raise the risk of venous and arterial thrombosis. The authors adjusted for surgical procedures, age, sex, hospital, smoking, BMI, and comorbidities. After adjustment, RBC transfusion did not statistically increase the risk of thrombosis (hazard ratio, 1.00; 95% CI, 0.96-1.05).

Increased risk for thrombosis in some patients may be related to underlying risk factors and the surgeries themselves rather than RBC transfusion, the authors concluded. The authors did not include patients with a history of thrombosis, patients with thrombosis within 24 hours of admission, and admissions after a thrombotic event, which lead to some limitations in the study. The authors did not conclude whether RBC transfusion increases the risk of thrombosis in patients with a previous history of thrombotic events.

“RBC transfusion was not an independent predictor of arterial and/or venous thrombosis,” the authors wrote. “Our findings do not rule out the possibility of a patient subset where RBC transfusion increases risk for thrombosis, such as patients with an underlying genetic hypercoagulable risk, but they do indicate that RBC transfusion does not appear to be an important risk factor for thrombosis in most patients.”

Disclosures: Some authors have declared affiliations with or received grant support from the pharmaceutical industry. Please refer to the original study for a full list of disclosures.


Baumann Kreuziger L, Edgren G, Hauser RG, et al. Red blood cell transfusion does not increase risk of venous or arterial thrombosis during hospitalization. Am J Hematol. Published online October 29, 2020. doi:10.1002/ajh.26038