Ensuring a safe blood supply: Part I (Proceedings)

A safe and adequate supply of blood components for transfusion is indispensable. The American Association of Blood Banks has established acceptable standards for the collection, processing, storage, distribution, and administration of human blood and blood components. Each blood bank and transfusion service strictly follows these standards, as well as certain legal requirements of local, state, and federal governments. Strict compliance with these standards reflects a commitment to providing quality products and appropriate care for patients receiving transfusion support. Although government organizations play less of a role in ensuring quality practices in veterinary medicine, the industry is striving to adhere to similar standards. To that end, the American Association of Veterinary Blood Banks and Association of Veterinary Hematology and Transfusion Medicine have established standards in veterinary transfusion medicine and blood banking that guarantee safety and efficacy. Given that blood is a live tissue, adverse events can occur at any time during donor selection and screening, blood collection, component processing and product storage.

Donor Screening

Most veterinary practices depend on voluntary donors to provide the blood necessary to meet the needs of the patients they serve. The donor screening process is one of the most important steps in protecting the safety of the blood supply. The process of blood donor selection is designed to provide you with information as to whether a donation of whole blood at this time will be harmful to the donor or if blood drawn from this donor at this time could potentially be harmful to the recipient. With this in mind, guidelines should be established that are designed to protect both the donor and the patient.

In human blood banking, it is recognized that the safety of the blood supply is critically tied to the quality and effectiveness of the predonation medical history, physical exam and donor testing. There are some minor differences as to which tests are needed, especially when it comes to the infectious disease screen. Once a donor is accepted into the program, careful and consistent monitoring of these screening tools is necessary. Each major step of the testing and processing system must be documented and the records maintained so that any blood product can be traced back to both the donor and the recipient.

There are specific requirements canine donors must meet before being accepted into the program. Donors must be a minimum of one year of age and weigh at least 25 kilograms to allow for the collection of a full unit (i.e., 450 ml ± 10%). They must be healthy and have a current vaccination status for distemper, hepatitis, parainfluenza, parvovirus and rabies. A four-week resting period is required following vaccination before a dog can donate; however, dogs can be safely vaccinated at any point after donation. Dogs are ineligible to donate if they are currently taking any medication (e.g., antibiotics, anti-inflammatory drugs, antihistamines). The majority of infectious diseases in the dog are transmitted by fleas, ticks and mosquitoes; therefore, for the safety of the donor and the blood supply, flea, tick and heartworm prevention is strongly encouraged. Dogs will also be disqualified from the blood donor program if they have ever been diagnosed with any of the following: heart murmur or other cardiac conditions, seizures or seizure-like activity, heartworm disease, chronic illness or a disease/condition that required a blood transfusion. Intact bitches cannot donate blood if they are in estrus. As canine donors are not sedated for blood collection, donor temperament is critical to the success of the blood donation. The collection process takes approximately five minutes, during which the dog is lying on its side—a very submissive position, and one that many dogs will not tolerate. Any dog that is anxious or fearful will not do well with the blood donation process.

On an annual basis, a complete blood count, serum biochemistry profile, and testing for geographically specific infectious agents (e.g. Ehrlichia canis, Babesia canis, Dirofilariasis immitis) should be performed. The hematocrit or hemoglobin concentration should be ≥40% or ≥13.5 gm/dl, respectively, prior to each donation. Blood donor dogs should be typed for Dog Erythrocyte Antigen (DEA) 1.1, and possibly other blood groups. The most severe antigen-antibody reaction is seen with this antigen. Significant naturally occurring alloantibodies are not seen in the dog; therefore, antigen-antibody reactions are not likely to occur on initial transfusion. However, dogs that are DEA 1.1 negative can develop alloantibodies to DEA 1.1 from a mismatched transfusion. This can occur within as few as 4 days from initial transfusion. These antibodies can potentially destroy the donor's red blood cells (i.e., delayed hemolytic transfusion reaction), ultimately minimizing the benefits of the transfusion. Because of the strong antigenicity of DEA 1.1, typing of donors and recipients for DEA 1.1 is strongly recommended. DEA 1.1 negative blood can be given to DEA 1.1 negative and DEA 1.1 positive patients. Dogs positive for the DEA 1.1 antigen can be accepted as blood donors as long as recipients are typed before administration, with DEA 1.1 positive blood being given only to patients positive for DEA 1.1. In an emergency situation or with specific medical conditions that preclude conclusive typing (autoagglutination in an IMHA patient), DEA 1.1 negative blood should be used to avoid sensitization to the DEA 1.1 antigen.

The approach to the feline donor is much more complicated than with its canine counterpart. At present, there are few commercial feline blood banks. In addition, volunteer programs for cats hold many risks. Although dogs will donate blood voluntarily, the majority of cats must be sedated for blood donation purposes. The legal ramifications associated with sedating personal pets for blood donation is far too great. Another concern is that cats can harbor infectious agents more readily than dogs. Because of this, only 100% indoor cats should be used.

Feline blood donors should be young, good-natured adults. They should be large and lean, weighing at least 5 kilograms. Good health can be verified through a medical history, physical exam, and routine laboratory testing. Donors should have current vaccination status for rhinotracheitis, calicivirus, panleukopenia, and rabies. Annual laboratory screening includes: complete blood count, serum biochemistry profile, feline leukemia virus, feline immunodeficiency virus, Mycoplasma haemofelis, and Mycoplasma haemominutum. Prior to each donation, donor hematocrit (≥35%) or hemoglobin (≥11 gm/dl) is checked.

One blood group system, the AB system, has been recognized in the cat. It contains three blood types: A, B, and the extremely rare AB. Nearly all domestic short hair (DSH) and domestic long hair (DLH) cats have type-A blood, the most common. Many purebred cats (and some DSH) have been identified with type-B blood. The proportion of A and B type varies not only among the different breeds, but also geographically. Cats differ from dogs in that they have significant naturally-occurring alloantibodies against the other blood type. Cats with type-B blood have very strong naturally-occurring anti-A alloantibodies, whereas type-A cats have relatively weak anti-B alloantibodies. Because of the presence of naturally occurring alloantibodies, there is no universal blood type in the cat. All feline blood donors and recipients must be blood typed, and only typed, matched blood should be administered. The extremely rare blood type-AB cat can be safely transfused with type-A packed red blood cells if type-AB blood is not available.

Blood Collection

Blood Collection Systems

Quality should be the primary goal in the collection, processing, storage and administration of all blood products. At each step, it is critical that practices must prevent or delay adverse changes to blood constituents, and minimize bacterial contamination and proliferation. Many improvements in the preparation of components from whole blood have been described.

Whole blood is most often collected into commercially-available plastic bags (Baxter Healthcare Corporation, Fenwal Division, Deerfield, IL; Miles, Inc., Cutter Biological Division, Elkhart, IN; Terumo Medical Corporation, Somerset, NJ). These sterile bags are considered "closed" collection systems in that they allow for collection, processing, and storage of blood and blood components without exposure to the environment, which diminishes the risk of bacterial contamination to the product. These systems are available in a variety of configurations that will determine blood component preparation and storage. They all meet human blood banking standards and have been tested successfully in veterinary medicine.

A single blood collection bag is used for the collection of whole blood when it is to be administered as whole blood. It consists of a main collection bag containing anticoagulant-preservative solution and integral tubing with a 16-gauge needle attached. This system is not recommended for component preparation in that the bag must be entered to harvest components, risking environmental exposure and potential bacterial contamination. If the bag is entered, the definition of this system then becomes "open", and the product must be used within a 24-hour period. Other collection systems consist of a primary collection bag containing anticoagulant-preservative solution and one, two, or three satellite bags intended for component preparation. One of the satellite bags may contain 100 ml of an additive solution used for red cell reconstitution following plasma removal. Additive solutions (i.e., saline, dextrose, adenine) extend packed red blood cell storage time.

In the dog, blood may be collected using the commercially-available human blood collection bags; however, the size of these systems prohibit their use in cats. Currently, smaller closed collection systems are not commercially-available. Unfortunately, as a result of the lack of closed blood collection systems for cats, the difficulty in preparing blood components from small whole blood units, and limited storage time allowed for blood collected with an "open system", cats in need of transfusion support most often receive fresh whole blood.

By modifying current blood collection protocols, the Penn Animal Blood Bank has developed a closed collection system for small blood volumes (35-50 ml) by using commercially-available blood collection products. All connections are established and sterility is maintained by using a tube-welding instrument (Terumo Sterile Tubing Welder 312®). These closed systems now allow for collection, processing, and storage of feline blood components.

Vacuum glass bottles containing ACD anticoagulant-preservative solution have been the most popular collection system used in veterinary medicine (for dogs). Although blood collection is easier with this system, there are many limitations and disadvantages: this is considered an "open" collection system, the glass activates platelets and certain clotting factors, the foam created during collection will disrupt the red cell surface and cause hemolysis, and component preparation is not possible. For these reasons, vacuum glass bottles are not recommended. Vacuum chambers that allow for more rapid collection into blood collection bags are available.

Anticoagulant-Preservative Solutions

There are several anticoagulants, anticoagulant-preservatives, and additive solutions available for blood collection for transfusion purposes. The primary goal of preservative solutions is to maintain red cell viability during storage and to lengthen the survival of red cells post transfusion. According to AABB standards, seventy-five percent of transfused red blood cells must survive for 24 hours following infusion in order for the transfusion to be considered acceptable and successful. The longer cells are stored, the more viability decreases. Predetermined storage times are based on studies that have investigated adverse biochemical changes that take place during red cell storage. These changes, referred to as the "storage lesion", include a decrease in ATP, pH, and 2,3-DPG (2,3-DPG loss occurs only in dogs) and an increase in the percentage of hemolysis. All of these ultimately lead to a loss of red cell function and decreased viability. Storage time will vary with the anticoagulant-preservative solution used.

Blood Storage

The shelf-life of blood components is determined by the type of system used for blood collection, the anticoagulant-preservative solution used, the time between collection, processing, and storage, as well as the temperature and conditions under which products are stored. It is critical that appropriate temperatures are consistently maintained in order to secure the quality of both red cell and plasma products. Refrigerators and freezers for blood component storage should be dedicated for this purpose, and evaluation of their temperature should be performed daily. Commercially-available blood refrigerators and freezers are built to continuously monitor and record temperature, with audible alarm systems that activate before blood products reach unacceptable temperatures.

References available upon request