In a population of patients without severely impaired baseline renal function receiving fewer than 10 erythrocyte units, duration of blood storage had no effect on the incidence of posttransfusion acute kidney injury (AKI).

The 14,461 patients included in this substudy received 40,077 erythrocyte units.

For patients who received more than one unit, the mean age of the blood units was used as the exposure.

The median of the mean age of blood units transfused per patient was 11 days in the freshest available blood group and 23 days in the oldest available blood group.

In the primary analysis, posttransfusion acute kidney injury was observed in 688 of 4,777 (14.4%) patients given the freshest available blood and 1,487 of 9,684 (15.4%) patients given the oldest available blood, with an estimated relative risk (95% CI) of 0.94.

The secondary analysis treated blood age as a continuous variable (defined as duration of storage in days), with an estimated relative risk (95% CI) of 1.00 for a 10-day increase in the mean age of erythrocyte units.

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