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Analysis of avian blood begins with the collection of the blood sample. Critical to this process is the volume of blood that can safely be removed, the sites for venipuncture, and the collection equipment and anticoagulant to be used.
The amount of blood that can safely be removed from a bird will depend on the size of the animal, and its health status. The total volume of a bird's blood is 10% of its body weight. 10% of this amount can be safely removed if the bird is healthy. For example, a 50gram budgie would have a total blood volume of 5ml. 10% of this, or .5ml can be safely removed if the bird is healthy. In the case of a bird that is ill, a reduced amount would be taken.
Sites for Venipuncture
There are a number of sites for blood collection from an avian. The site selected can be determined by the preference of the veterinarian or technician. Samples can be collected from the jugular vein, the cutaneous ulnar vein, the caudal tibial vein, the toenail, a skin puncture, the heart or the occipital sinus. Blood collected from the heart or occipital sinus can result in injury or death, so these methods are only used for blood sampling prior to necropsy. The safer methods will be discussed here.
In avians, the right jugular vein is larger than the left and blood withdrawal should be attempted here first. There is a featherless tract in many species that runs over the jugular vein. The feathers can be moistened with alcohol or water to allow visualization of the vein. Gently extending the neck causes the jugular vein to fall into the jugular furrow. Digital pressure can be applied to the furrow at the base of the neck to cause the vein to rise for easier visualization. As the jugular vein is very mobile it is a good idea to stabilize it with a finger prior to blood withdrawal. A needle and syringe can be used. Be sure to hold off the vein after collection to prevent hematoma formation.
The cutaneous ulnar vein can be located just below the skin on the ventral surface of the elbow joint. Digital pressure on the vein proximal to the collection site will cause the vein to rise for better visualization. Minimal pressure should be used when withdrawing the blood as the vein can collapse if too much pressure is used. A needle and syringe can be used. After collection, special care should be taken to hold off the vein to prevent hematoma formation, which is a common occurrence when blood is collected from this site.
This vein is located on the inside of the lower leg, just above the ankle joint. Digital pressure on the vein proximal to the collection site will cause the vein to rise for better visualization. A needle and syringe can be used. There is no need to hold off the vein for as long a time as with other methods as it is surrounded by muscle, which helps prevent hematoma formation.
The nail should be carefully cleaned with alcohol to help preserve the accuracy of the results. Cut back into the quick and collect the blood into a microhematocrit tube. Do not hold the leg too tightly when restraining the bird as this could cut off the blood flow. Resist the urge to "milk" the vein as this could cause alterations in the cell populations. After the blood is collected, a hemostatic agent such as silver nitrate or ferrous subsulfate should be used. If a second nail needs to be clipped, use a nail on the same foot, as it will be sore and the bird can stand on their "good" foot with the tender foot tucked up into their feathers.
Collection Equipment and Anticoagulants
In most instances, a 1 to 3 cc syringe with a 25 gauge needle will be sufficient for blood collection. Some practitioners prefer collecting directly from the needle hub into a collection tube.
Ideally, a blood smear should be made without the use of anticoagulants, which can affect the blood cell morphology. In practice, however, it is often necessary to use an anticoagulant. In these cases, lithium heparin is preferred over EDTA, which has caused cell smudging and/or hemolysis in certain avian species.
When working with smaller avian species a microcollection tube should be used. These tubes are smaller in size, and contain less anticoagulant. Beckton Dickson Microtainer® brand microcollection tubes work well for this application.