Laboratory evaluation is often necessary in the first 24 hours after a transfusion to monitor the patient's condition. Wiesen and colleagues evaluated the changes that occur in blood chemistry after transfusion.

Thirty-nine adult patients who were scheduled to receive two units of packed red blood cells were included in the study. Patients were excluded from participation if they had hemolytic anemia or recent active bleeding. The following serum levels were checked before the transfusion and at 15 minutes, one hour, two hours and 24 hours after the transfusion: potassium, blood urea nitrogen, total bilirubin and lactate dehydrogenase.

Before the transfusion, the median bilirubin level was 0.7 mg per dL (11.97 μmol per L), and it increased to 1.4 mg per dL (23.95 μmol per L) at 15 minutes, one hour and two hours after the transfusion. By 24 hours after the transfusion, the bilirubin level had returned to pretransfusion levels. In nearly one half of patients, this represented a change from a normal value before the transfusion to an abnormal value in the hour following the transfusion. Similarly, lactate dehydrogenase levels started within the normal range, increased to abnormal levels in the two hours after transfusion, but returned to normal within 24 hours. The only other value that changed, but in a clinically nonsignificant way, was the blood urea nitrogen level.

The authors conclude that elevations in bilirubin or lactate dehydrogenase are not a cause for alarm, and abnormalities should not be aggressively evaluated unless the changes are not transient or are associated with new symptoms. Other blood chemistry abnormalities should not be attributed to receipt of packed red blood cells.