Can you provide information about code 78122--whole blood volume determination, including separate measurement of plasma volume and red cell volume? In this procedure, blood volume analysis is based on the concept of the indicator dilution technique, whereby a tracer substance (e.g., albumin I-131) is mixed into an unknown volume. An identical amount of tracer is placed into a known volume. By comparing the concentration of the indicator between the known and unknown volumes, an exact measurement of the unknown volume can be obtained. For blood count, spun microhematocrit, use CPT 85013 (blood count; spun hematocrit) in conjunction with CPT 78122, if performed.