Introduction Sodium citrate, a component of the anticoagulant-preservative, CPD, used in the storage of whole blood, prevents coagulation by interfering with calcium-dependent steps in the coagulation cascade (Hardwick, 2008). In the United States, one unit of whole blood is approximately 450-500mL, of which the concentration of citrate is approximately 0.042g/100mL (Potestio, et al., 2022). An unfortunate side-effect of sodium citrate administration, which can occur during whole blood transfusions, is hypocalcemia, which can lead to life-threatening complications–-tetany, seizures, ventricular ectopy, etc. Although hypocalcemia secondary to citrate toxicity is well-established in massive transfusions (Potestio, et al., 2022), little is known about how citrate affects calcium levels per a single unit of whole blood transfusion after it has been completely distributed throughout the human body. The average adult contains approximately 70mL/kg of blood (Lemmens, 2006), and a healthy adult heart pumps approximately 75mL of blood per heartbeat, with an average heart rate of 75 bpm, it would take approximately one minute to circulate the entire blood volume in an average-sized adult. It can be assumed that it would take approximately one minute for the amount of citrate contained in the anticoagulant-preservative to also circulate completely. Secondarily, Tactical Combat Casualty Care (TCCC) is a military program designed to reduce preventable deaths by providing guidelines for trauma assessment and care in the prehospital operational environment. TCCC guidelines include the walking blood bank, in which military members are provided empty blood transfusion bags with a known concentration of CPD to be used for emergency transfusions. Military members must estimate the total volume of blood received from the donor prior to transfusion to the receiver as the concentration of CPD is based on 450 mL of whole blood. If a military member underestimates or overestimates the volume of whole blood prior to transfusion, does this change the calcium concentration based on blood volume deviation from the 450 mL standard? Methods We will conduct a random controlled trial during the Valkyrie Emergency Whole Blood training program with the 1st Marine Division to evaluate the null hypothesis: Primary endpoint: H1: There is no statistically significant reduction of calcium levels after one transfusion of whole blood containing the anticoagulant-preservative CPD. Secondary endpoint: H2: There is no statistically significant effect on change in calcium levels based on blood volume deviation from the 450mL standard. The Valkyrie training course is conducted over a 5-day period, and the training consists of autotransfusion of one unit of whole blood. Each autotransfusion is conducted on a consented volunteer from the 1st Marine Division, conducted in accordance with the program's standing operating procedure for safety. They are given a Letter of Appreciation for their official military record for volunteering. A total of N of X will be completed. The techniques will be as follows; Control: Pretransfusion ionized calcium levels will be determined using iSTAT lab draw (N=20) Post-autotransfusion: Ionized calcium levels will be determined using iSTAT lab draw at 120 seconds after autotransfusion of one unit of volunteers' whole blood (N=20) Prior to autotransfusion, the volunteers’ ionized calcium levels will be determined utilizing the iSTAT lab draw to determine a baseline. One unit of the volunteers’ blood will then be drawn based on the Valkyre SOP. We will weigh each unit and determine the volume deviation from the 450 mL standard blood volume. The volunteer will then be auto-transfused with one unit of whole blood. After 120 seconds post autotransfusion, the amount of time for the volunteers’ body to circulate its entire volume twice, we will measure the ionized calcium level using iSTAT. We will then compare the pre-and-post autotransfusion ionized calcium levels for a significant change in calcium levels. Additionally, we will compare this delta to the blood volumes to determine if the deviation from the 450mL standard also affects changes.