Background: Canine packed red blood cells (pRBCs) can be stored under refrigeration for several days; however, cellular metabolism remains active inside the units, thus producing substances that affect their quality. Objectives: We aimed to evaluate hematologic, biochemical, and blood gas variable alterations that occur in canine pRBCs during storage, and their effects on recipient clinicopathologic parameters. Methods: The study was conducted in two phases. In phase I, 15 pRBC units containing CPDA-1 were stored for 28 days; samples were collected weekly from the units of days 0 to 28 to measure the packed cell volume (PCV), pH, partial pressure carbon dioxide (PCO 2), partial pressure oxygen (PO 2), concentrations of lactate and potassium, and the percent hemolysis. In phase II, another 22 canine pRBC units stored for different time periods (maximum of 21 days) were transfused, and the recipients were evaluated before and after transfusion for changes in clinical parameters (heart rate, respiratory rate, systolic arterial pressure, and rectal temperature) and hematologic variables (PCV, lactate and potassium concentrations, pH, PCO 2 , the ratio of arterial oxygen partial pressure to fractional inspired oxygen [PO 2 /FiO 2 ] ratio, oxygen saturation [SaO 2 ], base excess, and bicarbonate [HCO 3 ]). Results: In the pRBC units, the PCV increased from 70% to 78.33%, the lactate concentration increased 627%, the potassium concentration increased 183%, the percent hemolysis reached 0.69%, and the pH decreased 9% after 28 days. However, the dogs who received transfusions were not negatively affected. There was a significant increase in PCVs, and a significant decrease in heart rates. Conclusion: Canine pRBCs undergo hematologic, blood gas, and biochemical alterations during storage; however, the transfusion of pRBCs stored for up to 21 days increased PCVs without causing harm to the dogs.