- The value of testing must always be weighed against the stress of venipuncture since the critically ill bird may not be stable enough for restraint.
- Common venipuncture sites in the bird are the jugular, medial metatarsal, and basilic veins.
- In many avian species, including the parrot, the most common site for blood collection is the jugular vein.
- The basilic vein is a particularly useful site in larger bird species like raptors or in species that lack a featherless tract over the jugular vein such as pigeons and waterfowl.
- The medial metatarsal vein tends to be smaller than the basilic vein, but is particularly popular in birds that lack a featherless tract over the jugular vein like pigeons, waterfowl and other aquatic birds.
- To minimize the risk of hematoma formation, select the smallest gauge needle possible.
- Up to 10% of blood volume (or 1% of total body weight in grams) can be safely drawn from healthy birds. Smaller samples, measuring no more than 0.5% of body weight, should be collected from critically ill or anemic birds.
Blood work is considered a basic diagnostic test in every species, including birds. Venipuncture may be indicated for wellness screening, sample collection for DNA sexing, evaluation of the ill or injured bird, as well as collection of blood for transfusion.
Risk versus benefit
The risk of venipuncture must be weighed against the diagnostic value of the test. Critically ill birds may not be stable enough for restraint and coagulopathies may can be associated with certain diseases, such as liver failure.
The equipment needed for blood collection is basically the same as for other species, however some adjustments must be made for small patient size. Gather all equipment needed before restraining the patient.
- Cotton balls and/or gauze square
- Blood collection tubes, e.g. microtainers
- OSHA-acceptable sharps disposal container
- +/- Heparin
To minimize the risk of hematoma formation, select the smallest gauge needle possible. For birds weighing less than 50 grams, I recommend 27- or 28-gauge needles, such as that seen on insulin syringes. For birds between approximately 50 and 100 grams, a 26- or 27-gauge needle is a good choice. Select a 22- to 25-gauge needle for birds larger than 100 grams. Depending on the size of the bird and the venipuncture site selected, attach the needle to a 0.5, 1.0 ml, or 3.0 ml syringe. Heparin is sometimes used to pre-heparinize the syringe, however always check with your laboratory prior to sample collection.
You will also need alcohol or alcohol or saline-soaked cotton balls to part feathers. Usually a digit is used to hold off the vessel, however a cotton-tipped applicator can be useful in a tiny patient. Cotton balls and/or gauze squares can be used to apply pressure after venipuncture.
Place small blood samples into microtainers (BD Microtainer Blood Collection Tubes; Becton Dickinson and Company, Franklin Lakes, NJ).
Volume of the blood sample
The usefulness of diagnostic testing is limited by the quantity and quality of the blood sample. Depending on the species of interest, total blood volume is approximately 60-120 ml/kg body weight, however total blood volume is generally estimated as approximately 10% of body weight. Up to 10% of blood volume (or 1% of total body weight) can be safely drawn from healthy birds. For example, the blood volume of a 100-gram cockatiel is estimated to be 10 ml. A maximum 10% of blood volume or up to 1 ml can be withdrawn from a healthy bird. Smaller samples, measuring no more than 0.5% of body weight, should be collected from critically ill or anemic birds. Be sure to take the possibility of hematoma formation into account when calculating the volume of blood volume to be collected.
General tips for blood collection in the avian patient
- Although some clinicians routinely insert the needle bevel up (Jenkins 1997), Dr. Don Harris recommends insertion of the needle bevel down to reduce the risk of laceration (D. Harris, personal communication, 2005).
- Puncture the vein directly rather than approaching from the side.
- Break the seal on the syringe before beginning venipuncture to minimize the risk of wobbling the syringe and needle.
In many avian species, including the parrot, the most common site for blood collection is the jugular vein. The jugular may be the only vessel large enough to collect blood from small birds like passerine birds. Generally the right jugular vein is larger than the left jugular, although either vessel can be used. The jugular vein is easily accessed in its featherless tract, or apterylae, on the right side of the neck. This lack of soft tissue coverage means the jugular vein is easily visualized unless the patient is markedly overweight or hypotensive. Unfortunately this lack of soft tissue coverage also means the jugular vein is prone to hematoma formation. Serious bleeding can occur when the vein is inadvertently lacerated. Fortunately hematoma formation can often be averted with the use of careful, gentle technique and adequate restraint.
Although experienced avian veterinarians can collect blood without an assistant from small birds, weighing less than 200-300 grams, venipuncture of the right jugular vein generally requires two people. The bird is restrained in left lateral recumbency with the neck extended (Fig 1). The body, including the wings, is often restrained with the help of a towel around the body. The phlebotomist typically holds the bird’s jaw securely in one hand, while the handler holds off the vessel at the thoracic inlet (Jenkins 1997).
Part the feathers overlying the jugular vein and then use alcohol to keep these feathers out the way. Sometimes the head or neck must be repositioned for the vein to become more prominent. The vein is approached cranial to caudal. Introduce the needle at a shallow angle and rest the hand holding the syringe on top of the hand gripping the bird’s head. This will ensure that if the bird should suddenly move then everything (the head and needle) will move together—thereby reducing the risk of lacerating the vessel. Collect the blood sample using very gentle and gradual aspiration to avoid collapsing the vessel.
The basilic vein, also known as the cutaneous ulnar or “wing” vein (Fig 2), is visible just underneath the skin as it passes over the medial surface of the elbow. The basilic vein is particularly useful in larger birds like raptors or in species that lack a featherless tract over the jugular vein such as pigeons and waterfowl
To collect blood from the basilic vein, an assistant restrains the patient in dorsal recumbency on a padded surface with one wing extended. The phlebotomist extends, stabilizes, and supports the distal wing by grasping the carpus. Hold off the vessel by pressing down on the wing above the antebranchium. The needle is inserted medially at a point just proximal to the elbow (Fig 3) (Jenkins 1997).
Hematoma formation is more common with the basilic vein when compared to the jugular, but is rarely of serious consequence. To minimize the risk of hematoma formation, use gentle technique and apply pressure for several minutes after sample collection is complete.
Medial metatarsal vein
The skin overlying the medial metatarsal or caudal tibial vein is located on the medial surface of the leg as it crosses over the intertarsal (hock) joint and along the tarsometatarsus (Fig 4). The scale-like skin overlying the medial metatarsal vein is relatively thick and hematoma formation is much less likely when compared to the jugular vein or wing vein.
The medial metatarsal vein tends to be smaller than the basilic vein, but it is particularly popular in birds that lack a featherless tract over the jugular vein like pigeons, waterfowl and other aquatic birds, as well as many long-legged birds (Fig 5). The medial metatarsal vein is also sometimes used in larger psittacine birds.
Blood collection from the medial metatarsal vein is a two-person (or more) technique. Depending on the size of the patient and the length of its legs, the handler or even a third assistant extends the limb forward while grasping the limb just above the stifle. This hold effectively “hamstrings” the bird to prevent leg movement while holding off the vein. The phlebotomist then inserts the needle into the vessel at a shallow angle. Typically the needle is introduced near the hock where scales meet feathered skin.
The medial metatarsal vein is usually smaller than the basilic, which may decrease sample volume. For particularly small samples, a hypodermic needle can be inserted into the vein and blood is collected directly from the needle hub into capillary tubes.
Although a toenail clip is a simple, rapid approach for collecting small blood samples, it is not advised due to the pain associated with this procedure and frequent tissue artifact. For instance, if the bird steps in droppings, uric acid will contaminate the toenail and test results will be falsely elevated.
After sample collection, gently place a cotton ball over the venipuncture site before gently withdrawing the needle. Apply firm, steady pressure for a couple of minutes while holding the bird upright. Resist the urge to press down on the vessel vigorously, as this can actually squeeze blood out of the thin-walled, fragile vessel creating a hematoma.
Transfer blood drawn into appropriate tubes as soon as possible. Keep in mind that the large, avian erythrocyte is relatively fragile. To minimize the risk of hemolysis and other artifactual changes, disconnect the needle from the syringe before transferring the sample into a blood collection tube. Tubes containing anticoagulant should be gently inverted several times. Never shake or mix vigorously. Always check with your laboratory before handling avian blood samples. Some labs request that blood smears be made with fresh blood, that is free of anticoagulants. Finally remember that the large, nucleated erythrocyte will continue to utilize glucose after venipuncture. One advantage of heparinizing blood is that samples transferred to red top tubes do not need to clot, but instead can be spun down immediately to prevent artifactual hypoglycemia (Fudge 2000).