Blood can be used as such or be separated into its various components, the blood derivatives. Blood derivatives are an important aid in veterinary practice and, with the establishment of blood banks also in veterinary medicine, it has become easier to use the blood products best suited to the clinical needs of patients (for example, patients lacking red blood cells, with a clotting factor deficiency or with a low platelet count).
The bags used for the collection and separation of blood comprise a “mother” bag which contains the anticoagulant and into which the whole blood is collected, and one or more satellite bags, without anticoagulant, which receive the plasma (Fig. 1). The bags can usually contain 350 or 450 ml of blood and are, therefore destined for use in large dogs. The characteristics of the main blood derivatives used in veterinary practice are reported below.
Whole blood: this is blood as such, to which anticoagulant is added. It can be stored in a refrigerator for 3-5 weeks depending on the type of anticoagulant-preservative solution used.
The plasma is then removed and collected into a satellite bag. In this way a bag of packed red blood cells and a bag of plasma are obtained from one bag of whole blood. The haematocrit of the packed red cells can reach values of about 80-85%. Plasma can be stored in a refrigerator for 3-6 weeks, depending on the type of anticoagulant-preservative solution used. The red blood cells must be re-suspended in physiological saline (100 ml) before being transfused.
Fresh plasma: this is plasma separated within 8 hours of collection. It is obtained by centrifugation of the bag of whole blood and transfer of the plasma into a satellite bag. Fresh plasma contains albumin, globulins and a high concentration of clotting factors.
Fresh-frozen plasma: this is fresh plasma separated and frozen within 8 hours of collection. It is obtained by centrifugation and separation of the contents of the blood bag and can be stored in a freezer (at a temperature of -18°C or below) for up to 1 year.
Cryoprecipitate: this is a precipitate of fresh plasma obtained after centrifugation of the plasma. It contains von Willebrand’s factor, factor VIII, fibrinogen, fibronectin and factor XIII. It can be stored in a freezer (at a temperature of -18°C or below) for up to 1 year.
Platelet-rich plasma: this is plasma that contains a particularly large number of platelets, obtained by slow centrifugation of whole blood and subsequent separation into a satellite bag. It can be stored at a temperature of 24°C for 3-5 days on a platelet agitator, which keeps the bags under constant movement.
Suggested readings
- Day HJ, Mackin A, Littelwood JD Ematologia e medicina trasfusionale del cane e del gatto. Ed. UTET, 271-316, 2004
- Lanevschi A, Wardrop KJ, Principles of transfusion medicine in small animals. Can. Vet. J., 42, 447-454, 2001
- Weiss DJ, Wardrop J Schalm’s Veterinary Hematology 6th edition. Ed. Wiley-Blackwell, 711-756, 2010