A long-term follow-up of patients who underwent cardiac surgery in Sweden found there was no association between red blood cell storage times and estimated mortality at 30 days, two years and 10 years.

The researchers also noted there was no association between red blood cell storage times and adverse outcomes within 30 days of surgery such as acute kidney injury, acute respiratory distress syndrome or respiratory failure, serious infection, stroke and thrombosis or embolism.

Lead researcher Ulrik Sartipy, MD, PhD, of Karolinska University Hospital in Stockholm, and colleagues published their findings online in JAMA on Oct. 20.

“These results complement recent randomized trials in providing further reassurance of the safety of current blood storage practices,” the researchers wrote.

They analyzed data from the SWEDEHEART register and identified patients who underwent CABG and/or heart valve surgery in Sweden between 1997 and 2012. They obtained transfusion data from a nationwide register of blood transfusions and information on vital status and adverse outcomes from national health data registers.

Patients were classified as having received blood stored less than 14 days, between 14 and 27 days or between 28 and 42 days. The follow-up data was completed on Dec. 31, 2013.

Of the 47,071 patients who were transfused in connection with cardiac surgery, 36.6 percent received red blood cells stored less than 14 days, 26.8 percent received red blood cells stored between 14 and 27 days and 8.9 percent received red blood cells stored between 28 and 42 days. The remaining 27.8 percent received red blood cells stored in a mixture of the three categories.

The mean age of patients was 70, and 39.2 percent were women.

At the two-year follow-up, the mortality rates were 49.5 deaths per 1,000 person-years in patients who received red blood cells stored less than 14 days, 45.4 deaths per 1,000 person-years in patients who received red blood cells stored between 14 and 27 days, and 41.1 deaths per 1,000 person-years in patients who received red blood cells stored between 28 and 42 days.

The 10-year mortality rates were 42.1 deaths per 1,000 person-years, 42.2 deaths per 1,000 person-years, and 40.8 deaths per 1,000 person-years, respectively.

The 30-day mortality rates were 446.5 deaths per 1,000 person-years, 406 deaths per 1,000 person-years, and 306.9 deaths per 1,000 person-years, respectively.

Although the researchers mentioned that a weakness of the study was that allocation of fresh red blood cell units could have been related to patient prognosis, they said the possibility was remote.

“We do not believe this was the case because no such practice was in place, there were no major changes in blood storage during the study period, and blood storage was not associated with any important clinical parameters,” they wrote.