Serum potassium changes following packed red cell transfusions in newborn infants.

We studied the effect of packed red cell transfusions on serum potassium levels in sick newborn infants. In 11 transfusions the infants' serum potassium levels fell from a mean of 5.1 +/- 1.2 mEq per 1 (SD) to 4.9 +/- 1.2 mEq per 1 within 1 hour of the transfusion. Plasma potassium in stored packed red cells rose markedly within 48 hours of drawing. In spite of this, the transfusion of 10 ml per kg of packed red cells did not affect the serum potassium concentration in the newborn infant.