Avian and reptilian hematology: Scratching the surface (Parts 1 and 2) (Proceedings)
The title of this presentation is apropos, considering the fact that there are over 9,000 species of birds and nearly 8,000 species of reptiles. Knowing how different the hematology is between dogs and cats exemplifies how different eagle hematology may be from a parrot, or an iguana from a snake. As such, we truly are scratching the surface when talking about hematology of these species.
Every discussion involving hematology should begin with sample collection and handling. EDTA retains premium staining quality and morphologic preservation and is preferred in most cases. However, it will hemolyze or otherwise detrimentally alter samples collected from crows, jays and many reptiles, especially chelonians (turtles). For these species, heparin is a reasonable alternative. Ostrich blood fairs best in citrate however one should be aware of the 9:1 dilution effects. An added benefit to using heparin is that the same sample can be used for most biochemistry analyses. As with all species, regardless of the anticoagulant used, fill the tube at least half full (full for citrate), mix well, and prepare a blood film as soon as possible. Some recommend preparing a film directly from the needle so as to avoid anticoagulant-associated artifacts altogether. Films can be made using the wedge technique and clean beveled edge slides. Some prefer to use coverslips to minimize rupturing cells. Mixing one drop of 22% bovine albumin with 4-5 drops blood prior to film preparation will also minimize ruptured cells, however this will alter the sample for additional testing. The cells most commonly ruptured in our laboratory are erythrocytes, and while they may contribute to the complexity of evaluating a film, they shouldn't alter the accuracy of the differential.A good rule of thumb for blood collection volume is 1% of the animal's weight if collecting no more frequently than every other week. This works out to .8 ml for an 80 g animal. If the animal is very ill, or if sampling will be more frequent, taking half or less that volume is necessary. There are many sites that can be used for blood collection and ideal sites vary between species. The most common for birds and turtles is probably the right jugular, as it tends to be the largest and most readily accessible vein. It is also less likely to be diluted with lymph in reptiles. Another common site for reptiles is the tail vein. Toe-nail clipping is not recommended.
The first examination of a blood film from a bird or reptile can be overwhelming since all the cells are nucleated. It is recommended that when first examining a film, pause a minute and review all the cells present for staining characteristics and other hints as to the cell types present before initiating the differential count.
There are some similarities between avian and reptilian hematology and common mammalian species including the basic cell groups of granulocytes, lymphocytes and monocytes. However, within granulocytes, birds and reptiles have heterophils rather than neutrophils. These are typically the most common cells observed in bird samples. Mature heterophils have oval to rod-shaped, reddish granules that often obscure a purple-staining lobed nucleus and colorless cytoplasm. Immature heterophils may appear with inflammation. Band forms are difficult to identify because the nuclear shape is obscured by the granules, therefore, myelocytes and metamyelocytes are more frequently observed and are identified by more deeply basophilic cytoplasm, fewer granules, immature granulation (blue-purple rounded granules), and round to indented nuclei. Toxic changes may also be observed in animals with severe systemic disease. Mild to more severe toxic changes, in order, include increased cytoplasmic basophilia, vacuolization, degranulation, large fused granules, and smudging of nuclear detail.
Heterophils may be mistaken for another granulocyte, eosinophils. Eosinophils can usually be identified by the numerous, intensely pink, usually round, cytoplasmic granules, although the shape and color of granules may vary somewhat between species. Eosinophil granules of psittacines and iguanas typically stain blue to lavender and staining artifacts may create swollen, rounded granules in various specimens. Eosinophils have a more deeply basophilic cytoplasm and also have a lobed nucleus that may be obscured by granules.
Avian and reptilian basophils are more commonly observed than in mammals and contain purple or metachromatic granules and have an oval to round rather than lobed nucleus. These appear very similar to mammalian mast cells. Quick stains, Romanowsky stains, and heparin may alter the staining and/or retention of granules however there are usually at least a few granules visible to help identify these cells.