- Parameters for transfusions and causes of anemias in birds are similar to other species. Transfusions should be given when the PCV is below 20%, especially with chronic anemia.
- Blood type information is unknown in most species and therefore cross matching should be performed before giving a transfusion.
- The ideal donor should be of the same species or as closely related as possible as this affects the survival time of the transfused cells.
- Standard transfusion media can be used in birds.
Avian erythrocytes are oval, nucleated, and considerably larger than mammalian erythrocytes (Fig 1). The avian red cell is typically 10 to 15µm in length; whereas the typical mammalian erythrocyte is biconcave and 6 to 7µm in diameter. The lifespan of the avian erythrocyte is 28 to 45 days, compared to the human erythrocyte that lives 50 to 60 days. This shorter life span is thought to be a function of the increased metabolism and higher body temperature of birds. The avian erythrocyte can consume seven to ten times more oxygen at room temperature than the mammalian erythrocyte.
Total red blood cell numbers in birds are affected by age, sex, environment, hormonal influences and hypoxia. Red cell numbers tend to be lower in young birds and females. The packed cell volume (PCV) for most species ranges from 35-55%. A PCV less than 35% is considered anemia. Reticulocytes can be measured as an indication of the response to an anemia. The normal reticulocytes count in most species is 1 to 5% of erythrocytes. Diffuse polychromasia is common in avian erythrocytes although the amount may still be qualified as an indication of regeneration.
Anemia in birds is caused by many of the same mechanisms as in mammals such as decreased production, increased destruction, or blood loss. Decreased production is often seen as an anemia of chronic inflammation. Birds develop this type of anemia more quickly than mammals because of the shorter lifespan of the avian erythrocytes. More avian erythrocytes are destroyed on a daily basis therefore alterations of erythroid production are seen earlier. Hemolytic anemias are less common in birds but can be caused by toxicities, hemoparasites, and septicemia. Immune-mediated anemias have not been reported in birds.
Hemorrhagic anemias are common in birds secondary to injuries. Healthy birds are remarkably adept at dealing with acute blood loss and hemorrhagic shock rarely occurs. Studies in chickens have shown that after removal of 30% of the blood volume, the PCV returns to normal within 72 hours. Removal of 60% of blood volume in pigeons did not cause significant clinical affects and resulted in a return to normal PCV by day 7.
The decision to administer a transfusion is based on several factors: PCV, chronicity of anemia, cause and severity of anemia, possibility of further blood loss (either by hemorrhage or diagnostic purposes), and the ability of the patient to tolerate the stress associated with transfusion administration.
Mild to moderate anemias of a chronic nature may not require transfusion if the patient is stable and will not require extensive hematologic testing (which will effectively worsen the anemia) or surgery. Cases of severe anemia (<15%) may benefit from a transfusion because the patient may be stabilized while diagnostic testing to determine the cause of the anemia is performed.
Antigens on the erythrocyte membrane determine blood grouping. At least 28 different blood group antigens have been found in the chicken. Blood group antigens have also been studied in pheasants, quail, turkeys, guinea fowl, and ducks. There is no information on blood grouping in psittacine birds or other pet species.
Compatibility and donor selection
Because of a lack of identified blood groups in companion bird species, compatibility for transfusion is based on the use of major and minor cross matches. A major cross match is performed by mixing donor red cells with recipient plasma and a minor cross match uses recipient cells and donor plasma. The appearance of agglutination or cell lysis indicates incompatibility.
Unlike mammals, a single transfusion between different bird species can be safe and efficacious. Transfusions will be most effective if the donor is of the same species. Several studies have shown homologous transfusions to have a longer red blood cell survival time when compared to heterologous transfusions. Heterologous transfusions between members of the same genus may have similar survival times (L. Degernes, pers.com.). Therefore, the recommended donor is the same species or, if that is not possible, the same genus. The half-life of heterologous transfusions may range from 12 hours to 3 days whereas a homologous transfusion may have a half-life of 6 to 11 days.
With the number of avian species presented to clinicians, keeping a large variety of blood donors is impractical. A feasible option for many practices is to have a list of client-owned, healthy birds of a variety of species to use as donors when necessary. All donor birds should be screened by yearly physical examinations, complete blood counts, and biochemical profiles. Donors should also be screened at least once for infectious diseases that are pertinent to the species.
Blood collection and storage
The site of blood collection from the donor depends on the size and species of bird used and the amount of blood needed. In general, it is safe to withdraw approximately 10% of the blood volume, which is approximately 1% of the body weight. For example, a 500g Amazon parrot can have 5 ml safely removed.
For psittacines, ratites, and soft bills the right jugular vein is the most reliable and readily accessible site for blood collection. In waterfowl and gallinaceous birds, the medial metatarsal vein is easily identified on the medial aspect of the lower leg and can be used for blood collection in addition to the jugular vein. The basilic or wing vein can be visualized as it crosses the proximal ulna. The basilic vein can be used in most species, especially pigeons, doves, and some raptors, however this vessel may be smaller and more fragile than other veins.
Blood may be collected directly into syringes containing an anticoagulant. The anticoagulant of choice is sodium citrate, although heparin, acid citrate dextrose (ACD), or citrate phosphate dextrose (CPD) can also be used. Sodium citrate is added to the syringe before collection of the sample at 0.1cc of citrate per 0.9cc of blood to be collected. A similar volume of ACD or CPD can be used. Take care when transfusing smaller species or patients with hypocalcemia when using these media because they act by binding calcium in the blood. Heparin can be used safely at 0.25ml per 10ml of blood collected.
Blood is collected into a syringe using a needle or butterfly catheter. A small amount of anticoagulant should be flushed first through the needle to prevent clotting. The author has used blood stored in ACD and citrate for 12 to 24 hours without apparent deleterious effects. Long-term storage of avian blood is not currently practiced. Mammalian storage media are inadequate for storage of avian whole blood because of the differences in erythrocyte metabolism.
The amount of blood administered will depend on several factors including the degree of anemia, the size of the donor, and stability of the recipient. As a guideline, the amount of blood transfused should be approximately 10-20% of the blood volume of the recipient, which is approximately 1-2% of the body weight.
The blood sample may be administered to the recipient directly from the collection syringe (Fig 2) or, for larger amounts from a pediatric transfusion bag. Transfusions may be given intravenously (IV) or intraosseously (IO) as a bolus or by constant rate infusion. The infusion method is less likely to cause circulatory overload but requires the placement of an indwelling IV or IO catheter. The transfusion is given over 2 to 4 hours. A blood filter can be used to remove clots or other large material from the transfusion. The filter pores are typically 18µm in diameter, which should accommodate the 10 to 15µm avian erythrocyte although the potential of the filter to cause cell lysis has not been determined.
The bolus method of transfusion delivery has the advantage of requiring only temporary venous access but can cause circulatory overload and may require longer handling time. The transfusion should be given IV or IO over 1 to 5 minutes if using the bolus therapy.
Transfusion reactions are caused by incompatibility of donor red cells with host plasma. Transfusion reactions may result in hemolysis of donor cells, fever, and urticaria. These signs may be difficult to assess in avian patients, and death may be the only adverse effect observed. Transfusion reactions have been reported in birds given three heterologous transfusions at two-week intervals. Pathology showed changes consistent with transfusion reactions such as hemoglobin casts in the renal tubules. Regurgitation has also been seen and was thought to be a result of administration of the transfusion too quickly or in too large a volume. The risk of reactions can be reduced by cross matching.