Transfusion medicine and the use of blood products have become extremely valuable treatment options in emergency and critical care situations. Our knowledge and ability in selecting and administering suitable blood components for specific disorders and conditions have advanced. Some examples of these advancements include using red blood cells (RBCs) for anemia to supplement oxygen carrying capacity, plasma and its contents to provide coagulation factors in coagulopathies, and platelets to aid in hemostasis in patients with life-threatening hemorrhaging due to thrombocytopenia. In addition, supportive evidence is emerging for canine-specific albumin to positively affect the outcome in hypoalbuminemic patients. Less commonly, intravenous immunoglobulin (IVIG) is administered for its immunomodulatory effect in immune-mediated hemolytic anemia (IMHA), immune-mediated thrombocytopenia (ITP), and sudden acquired retinal degeneration syndrome. Furthermore, specific immunoglobulins are utilized as antitoxins for snake envenomation and tetanus. Providing these products poses a real challenge as the supply is limited by donor availability and our ability to process the blood into its components. Commercial blood banks have an increasingly available supply and variety of blood products, though are not exempt from resource limitations. Veterinary practices would benefit from making a conscious choice about how to supply and administer blood products in a practical manner.

Practical Banking

Equipped with the knowledge of the various blood products available, a veterinary practice must decide the most practical and reasonable way to provide patients with the best course of treatment. The method of supplying blood products will be strongly influenced by the type and size of the practice. Historically, it has not been uncommon for a practice to have a “hospital cat/dog” or to have the pets of staff members donate their blood (whole blood) for the patients. While many lives have been saved this way, it is difficult, with current knowledge and availability of blood products, to recommend this method except in dire circumstances. If caught in a situation where blood products are unavailable, seeking help from a nearby practice with an in-house blood bank to obtain blood products or referring the patient may be available options.

In-House Banking

The next logical step is to store blood products at the practice as an in-house blood bank. Larger practices or emergency specialty practices are more likely to have an in-house blood bank, as the need for blood products arises more frequently. This can be accomplished with a blood banking-specific storage system or a simple household refrigerator and freezer. A variety of blood products can be purchased from commercial blood banks.

Since blood products have limited shelf lives, financial viability is a real concern. In an ideal situation, every blood product should find its way into a patient in a helpful manner prior to its expiration, without ever having a patient wait for the product any longer than necessary for appropriate testing. After all, the purpose of an in-house bank is to have our blood components available to us swiftly when needed. By maintaining transfusion logs or reports, usage of these products can be tracked and help the practice fine-tune their supply based on historic demand. Unfortunately, even with the most diligent planning, it is unlikely we will prevent all situations of blood component unavailability.

Donor Selection

It is at this point that the practice should evaluate taking the next large step in blood banking, which is to set up and maintain a blood donor program. While this may feel like a huge endeavor, donor programs can vary in scope and size. If the decision is made to move in this direction, a practice can start at a smaller scale to supply their basic needs while products requiring more investment can be purchased from commercial banks. There are some minimal requirements of a donor program, regardless of its size, noted below:

General Screening

A blood donor must be screened based on multiple criteria. First and foremost, the health of the donor is determined so the donor is not harmed by donating. A veterinarian will conduct a full physical and health exam on the potential donor. Complete blood chemistry, urinalysis, and complete blood counts should be run on each potential donor prior to admittance into the donor program. This helps rule out any underlying systemic disease which will make the donor unsuitable to donate.

Blood Typing

Ideal canine blood donors possess blood that will not cause an immunologic reaction when transfused to any random canine recipient (the concept of a “universal” donor). In canines, 98% of the population has been reported to be positive for DEA 4. Because of this, potential donors that are negative in all but DEA 4 (“DEA 4 positive only”) are considered to be ideal for donation. Dogs that are DEA 1 positive but still negative in every DEA aside from DEA 4 can be considered to enter the donor pool. They will provide blood for patients that are DEA 1 positive and stable enough to be blood typed prior to transfusion. Extensive DEA typing is offered by commercial laboratories (though DEAs other than 1, 4, 5, and 7 are unable to be typed due to antisera being unavailable) and is recommended for canine donors entering a donor program. Typing for DEA 1 with a point-of-care typing kit as the only blood typing for canine donors may be the protocol implemented by banks because other DEAs rarely cause clinically significant transfusion reactions. Other antigens such as Dal and Kai are known to exist, though typing is not readily available.

Feline donors of both type A and B blood are necessary. The majority of felines are type A, but a small portion of the population are type B, or on very rare occasions type AB. An antigen called Mik (though currently unable to test in-house) has been described, and may be responsible for hemolytic transfusion reactions in type-matched blood transfusions. Naturally occurring antibodies against different AB blood group antigens in cats leading to severe transfusion reactions require blood banks to keep both type A and type B feline blood on hand. The rarity of type B poses a difficulty in having blood components of the type on hand, making type B donors very valuable to have in your donor pool. Point-of-care blood typing kits for felines are reported to be accurate and are inexpensive, allowing for typing solely in-house.

Bloodborne Pathogen Screening

Canine blood is to be screened for heartworm, and other pathogens. The ACVIM consensus statement issued in 2016 recommends screening for babesiosis, leishmaniasis, ehrlichiosis, brucellosis, anaplasmosis, neorickettsiosis, trypanosomiasis, and bartonellosis. Feline blood is to be screened for FeLV and FIV, as well as other pathogens. The ACVIM consensus statement issued in 2016 recommends screening for hemoplasmosis, bartonellosis, cytauxzoonosis, ehrlichiosis, anaplasmosis, and neorickettsiosis. Feline donors should be kept strictly indoors to eliminate interactions with potentially infected cohorts. Commercial blood banks and veterinary teaching institutions such as Antech Laboratories, Animal Blood Resources International, and UC Davis provide blood screening services (some offer blood typing and screening with a single submission). This screening should be repeated at least on an annual basis and the donor removed from the donor program if positive results are seen.

Other Factors

Any previous transfusions will exclude the candidate from becoming a donor. While we are unclear how long antibodies produced from previous transfusions remain, currently accepted recommendation is to remove them from the donor pool. In the past, pregnancies were thought to induce production of antibodies against fetal blood in the mother, making their blood unsuitable for transfusions. A study in 2009 has shown there is no significant antibody production through pregnancy, allowing previously pregnant dogs to stay in the donor pool. Donors of both species should also be selected for their level of cooperation. While blood components are valuable, it is hard to justify collecting blood from a “volunteer” donor who gets extremely stressed in the process. Many blood banks are successful at building a canine donor pool solely on donors who willingly donate without the need of sedation. Every canine donor program should aim to do so, as donating stress-free without any sedation is a good sign our canine donors are “volunteering” their blood. The use of sedation in feline donors still seems necessary, however, in order to have a stress-free donation.

Blood Donation

On the Day of the Donation

Prior to each donation, the donor should be evaluated for their eligibility to donate. Each donor should undergo a physical exam and have bloodwork (PCV or hemoglobin minimally) performed prior to donation to detect any health issues. A CBC may be performed to ensure an adequate HCT (>40% canine, >30% feline), hemoglobin (>13 g/dL canine, >10 g/dL feline), and platelet count (>200×10³/µL). Paying close attention to any sudden changes to these values is also important. As an example, if a greyhound that normally has a 55% HCT comes in to donate and has a 40% HCT on the day of donation, the greyhound should be examined further to determine a cause. If none is found the HCT should be rechecked at a later date (and pass on the donation this time around).

Canine donors can donate 19–22 mL/kg of blood once every 6–8 weeks (though many programs often give a longer recuperation time in between). Donors weighing greater than 55 lb will be able to donate 450 mL of blood (the required amount for commercially available multi-bag collection systems). The term blood “donation” implies a voluntary giving of the blood. In reality, our donors, at least initially, are volunteered by their owners to donate blood and usually require restraint. However, many of our canine donors will tolerate donating without sedation and with gentle handling and proper training, will learn to willingly donate. Blood donation will become a pleasant and routine experience. A quiet, secluded room should be set aside and regularly used as the donation room. Effort should be made to habituate the donor to the room by providing ample praise and treats. The collection process will require 2–3 people (one person for restraint, one person for the venipuncture, and an optional person to handle items surrounding the collection). The involvement of the owner should be gauged on an individual basis as some donors do well in the owner’s presence while others may not. The donor can be placed in lateral or sternal recumbency during the donation process. If a vacuum collection setup is used, the donor will be able to stay on the floor. If gravity-assisted collection is chosen, the donor will be placed on a higher surface (table, for example). The venipuncture area is gently clipped and prepped to minimize irritation. The venipuncture is performed with the blood tubing clamped to prevent entry of air into the bag. The clamp is removed once the needle enters the jugular vein. The progress of the collection is monitored with a gram scale. The goal is to collect 450 mL (474 g), though 405–495 mL (426–521 g) is allowable. If flow is disrupted, troubleshoot by adjusting the needle or working out occlusions. Gently rock the blood bag intermittently if using gravity-assisted collection. Once the desired amount is collected, re-clamp the blood line close to the needle, and remove the needle from the donor. Pressure should be applied to the venipuncture site and should be monitored until hemostasis is achieved. Donors typically will be able to get up and walk around the donation room. Complications such as hypotension, bruising or extravasation, and irritation of the clipped and prepped area may occur. Food and water should be offered. Donors should be restricted from exercising for at least 24 hours. Placing pressure on the jugular with neck leads should be avoided.

Feline donations are performed similarly, though sedation is almost always required for a stress-free collection. A ketamine/benzodiazepine or ketamine/opioid combination is commonly used. Great effort should be made in making the donation process as pleasant as possible. This effort starts with the owners making trips to the veterinary clinic a non-threatening process, and the medical staff being conscious of stress points during the cats’ stay and donation. Feline donors can donate 11–15 mL/kg of blood once every 6–8 weeks (though many programs often give a longer recuperation time in between). Donors weighing greater than 10 lb will be able to donate 50 mL of blood. Similar steps as canine donations are followed, with the major difference being the collection system used. Feline donations are collected through a “semi-closed” system; a sterilized assembly of a 19-G butterfly catheter, 60-ml syringe, and a 60–100-ml collection bag, connected through a three-way stopcock. An anticoagulant preservative solution (7–8 ml CPDA-1 for a 50-ml collection, for example) is added to the syringe just prior to the collection, leading to a “semi-closed” system, causing a compromise to the sterility. Administration of a crystalloid fluid through the subcutaneous or intravenous route is often performed for cats, as hypotension is more common in comparison to dogs.

Component Separation

Because component therapy is beneficial overall due to the ability to provide targeted therapy for specific diseases, eliminating unnecessary risks of transfusions, and efficiently using limited biological resources, component separation should be considered by any practice supplying themselves of blood products through donations. Component separation requires additional equipment and is a significant financial investment for a practice, but will allow a practice to be in better control of blood component supply, providing better care for their patients.

Storage

Blood components have different storage requirements depending on the product. Blood refrigerators are equipped with efficient and fast cooling mechanisms that control the temperature at desired levels. Plasma freezers easily maintain temperatures of −40°C or less. These storage devices can have built-in thermometers with history recording and alarm settings with remote notifications, allowing blood bank personnel to constantly keep tabs on the bank. Storage is another large financial investment for a blood bank, and in veterinary settings, many use a household refrigerator/freezer unit for their needs. This practice, while not completely ideal, is a realistic solution and viable as long as the storage units are used solely for blood products (preventing loss of temperature due to frequent opening and potential contamination) and temperature levels are monitored.

Centrifuge

A variable-speed, large-volume-capacity, and temperature-controlled centrifuge is necessary as standard equipment for processing blood components. A couple of prominent manufacturers of these centrifuges include Beckman-Coulter and Sorvall (Thermo Scientific). Benchtop and floor model centrifuges are available. Benchtop models are compact and have a smaller footprint, but typically require a higher rotation per minute (RPM) to create the required relative centrifugal force (RCF). Floor models have a larger footprint, but require lower RPM for the RCF required, improving stability. These centrifuges cost thousands of dollars, making purchasing of secondhand centrifuges not uncommon in veterinary applications. Depending on the model, controls may be quite simple (dial settings for temperature, RPM, and spin duration; computerized programmed pre-sets for spin settings).

Plasma Extractor

A spring-loaded plasma extractor is used to gently squeeze the blood bag after centrifugation in order to push the plasma out of the blood collection bag into a satellite bag. The even, gentle pressure this device provides makes plasma extraction more reliable without disturbing the centrifuged red blood cells. Plasma extractors cost $100–140, making them a relatively inexpensive investment.

Tubing Sealer

Aluminum sealing rings and a hand sealer can be used to crimp the tubing on the blood bag, pinching the plastic together, creating a barrier within the tubing where the crimps are applied. Aluminum seals are inexpensive to acquire, and the crimping mechanism is built in with the tubing stripper, making this a financially light option. Thermal tubing sealers replace aluminum rings, physically fusing the plastic to form a true seal, which is more certain in its ability to prevent contamination. Benchtop and handheld thermal tubing sealers are available on the market for a few thousand dollars, though acquiring one secondhand for far less may be possible.

Platelet Agitator

Platelet concentrate requires storage at room temperature and under constant agitation. This is achieved with a piece of equipment called the platelet agitator, which rocks the contents of the bag back and forth in a gentle side-to-side motion. A practice’s decision to purchase a unit will depend on whether the demand for platelet concentrate is high enough to justify the cost of regular processing and storage, given its short shelf life of 5 days.

Component Separation Process

Fresh Whole Blood (FWB)

FWB is simply blood collected that has not been altered and used within 8 hours of collection. FWB contains RBCs, platelets, labile and stable coagulation factors, albumin, and other plasma proteins. No processing or storage equipment is required for use of blood in this manner and is the most traditional method of use in a veterinary practice. Bags should be stored upright and rotated twice a week to allow mixing of nutrient-poor portions of the plasma with nutrient-rich portions through storage.

Stored Whole Blood (SWB)

If the collected blood is not due to be used within 8 hours, it can be stored at 1–6°C for 21–28 days depending on the anticoagulant-preservative solution (APS) used. SWB contains RBCs, stable coagulation factors, albumin, and other plasma proteins. The amount of labile coagulation factor decreases as time passes on. A temperature-controlled storage unit dedicated to blood products is necessary for SWB storage. Bags should be stored upright and rotated twice a week to allow mixing of nutrient-poor portions of the plasma with nutrient-rich portions through storage.

Packed Red Blood Cells (PRBC)

In order for packed red blood cells to be separated from plasma, blood should be collected into a collection system with a satellite bag. The bag undergoes centrifugation at 5000 x g RCF for 5 minutes (plus spin down time) for canine blood at 4°C. The plasma portion is transferred into one or two satellite bags with a plasma extractor, leaving a dense RBC portion. If no additive solution (AS) is added to the RBC, the PCV must remain lower than 80% by leaving 50 mL of plasma within the bag. If an AS is used, the maximum amount of plasma possible is removed. In canines, a donation of 450 mL blood typically yields 220–260 mL of RBC/AS solution mixture. This volume is typically divided into two separate bags to yield approximately 125-mL units. In felines, a donation of 50 mL of blood typically yields 15–20 mL of pRBC after centrifuging at 3000 x g for 10 minutes. Ten mL of AS solution is added to yield a 25–30-mL mixture, which is considered a feline pRBC unit. Special equipment required for this process includes a plasma extractor and a temperature-controlled centrifuge. Bags should be stored upright and rotated twice a week to allow mixing of nutrient-poor portions of the plasma with nutrient-rich portions through storage.

Fresh Frozen Plasma (FFP) and Frozen Plasma (FP)

The extracted plasma, which is placed in one or two satellite bags and frozen within 8 hours from collection (placed in the freezer before 6 hours to allow for freezing by 8 hours) is considered FFP. FFP contains both labile and stable coagulation factors. FFP can be stored for 1 year at lower than −20°C. If the plasma is not frozen within 8 hours, FFP is left unused for 1 year, or FFP is thawed but not opened, it can be stored as FP at −20°C for 5 years total. Frozen plasma products should be handled with care and storing them in storage cartons protecting the frozen plastic bags from cracking is recommended. The plasma can be stored vertically to allow visualization of any thawing that may have occurred during storage, especially if a household freezer is used (which achieves the minimum temperature needed for plasma product storage, and may have an auto-defrost cycle).

Cryoprecipitate and Cryosupernatant

Plasma can be separated into cryoprecipitate and cryosupernatant. The plasma is frozen as usual, except with an empty satellite bag attached to it. The plasma is then placed in a refrigerator at 1–6°C to slowly thaw until it reaches a slushy consistency (10% frozen). It is then centrifuged at 5000 x g for 7 minutes, and the supernatant is transferred to the empty satellite bag. The 10–15 mL of precipitate remaining is called cryoprecipitate, containing von Willebrand factor, coagulation factor VIII, fibrinogen, fibronectin, and factor XIII. The supernatant removed is called cryosupernatant. Both cryoprecipitate and cryosupernatant should immediately be refrozen and has an expiration date of 1 year. Administering desmopressin at 0.6 µg/kg diluted in 15 ml saline IV 30–60 mL prior to donation will result in an increased yield in vWF. The plasma can be stored vertically to allow visualization of any thawing that may have occurred during storage, especially if a household freezer is used (which achieves the minimal temperature needed for plasma product storage, and may have an auto-defrost cycle). Production of cryo-products for felines is typically not performed.

Platelet-Rich Plasma (PRP) and Platelet Concentrate (PC)

Platelets can be separated out from fresh whole blood through a two-step process. Fresh whole blood is centrifuged at a “light spin” setting. Settings are variable depending on blood bank protocols. Protocols utilizing 1000 x g for 4–6 minutes or 2000–2500 x g for 2.5–3 minutes at 20–24°C are seen. The platelets above the buffy coat are extracted into a satellite bag along with the plasma, referred to as PRP.

PRP can be centrifuged further with varying protocols such as 2000 x g for 10 minutes or 5000 x g for 5 minutes at 20–24°C and have all but 35–70 mL of platelet-poor plasma removed, to produce PC. This second spin creates platelet pellets, which are allowed to rest undisturbed for 1 hour to promote disaggregation of platelets. The pellets are gently broken down and resuspended through manual agitation. Once the platelets are resuspended, it is stored under continuous gentle agitation in a platelet agitator at 20–24°C. The required room temperature storage makes platelet products more prone to bacterial contamination, making them viable for only 5 days.

Platelet products are not typically processed with feline blood, though feline PRP has been observed to contain platelets with in vivo efficacy. Special equipment necessary for platelet processing and storage include a platelet agitator and possibly a blood tubing welder to add additional satellite bags for processing.

Donor Programs

If commitment in proper screening and simple forms of component separation can be made, there are various possibilities in acquiring your donor pool. An immediate option may be the hospital cat/dog and pets of the staff. Staff members may also have close friends or family members who are just as enthusiastic about canine or feline blood donation, aiding in the creation of an in-house donor program. Rescue organizations and various breed groups in the area could prove to be great allies in finding potential donors. A well-established blood bank may choose to operate a completely community-based blood donor program, taking volunteers from the public.

It is important to take to heart that a donor program (in-house or community) is based fundamentally on altruistic intentions of providing a life-saving resource to treat the critically ill. This makes our donors and their owners very special, and they should be treated as so. Donor programs often provide small tokens of appreciation and “goodie bags” to give to their donors at each donation, while others have “The Wall of Heroes” displaying photos of long-term donors. Some may consider providing a retirement gift after a dedicated career in blood donation. There are multitudes of methods as gestures of appreciation, showing our donors some gratitude.

Finally, a community program is an excellent way to make an additional positive connection and raise awareness of our increasing blood component needs. After all, the veterinary medical community, along with the pet-loving community is made up of individuals who share the passion of providing the best care for our furry (or sometimes non-furry) friends.

References

1.  Weiss DJ, Wardrop KJ. Schalm’s Veterinary Hematology. 2010:731–737.

2.  Day MJ, Kohn, B. BSAVA Manual of Canine and Feline Haematology and Transfusion Medicine. 2012:280–308.

3.  Yagi K, Holowaychuk M. Manual of Veterinary Transfusion Medicine and Blood Banking. 2016.