BACKGROUND AND OBJECTIVES: We should control free K MATERIALS AND METHODS: RBCs of 240-330 mL were prepared from whole blood donations, then split into halves and stored in SAGM solution at 4 ± 2°C for 21 days. RBCs were split and washed on Days 1 and 8, and some were gamma-irradiated on Day 8. Glucose, lactate, lactate dehydrogenase (LDH), adenosine triphosphate (ATP), K RESULTS: After washing on Day 1, only glucose and lactate improved, whereas after washing on Day 8, LDH and K CONCLUSION: K