Figure 1Canine with Marked Toxicity and Eccentrocytes
Reticulocyte count
The reticulocyte is the stage in the transformation of the erythroblast to the mature erythrocyte, where the nucleus has been lost. It takes about 24 to 48 hours after release from the bone marrow to become a mature erythrocyte. During this 48-hour stage, the reticulocyte contains precipitable ribosomal RNA, which can be stained with a supravital stain e.g. New methylene blue.
The number of reticulocytes is an index of red cell production by the bone marrow (regeneration) and as such, is one of the most valuable observations in diagnostic haematology.
Figure 2 Feline reticulocytes - New methylene blue stain
Heinz Bodies
Heinz bodies are denatured precipitated Hb on the surface of the red blood cell. Heinz bodies are easily visualised with supra vital stains such as new methylene blue and appear as dark, round protuberant bodies at the periphery of red blood cells.
Heinz bodies in cats, in small numbers are considered to be without clinical significance. Heinz bodies are formed when the natural mechanisms to prevent oxidation of haemoglobin in the red cells are overwhelmed. The most common causes are drugs, onion poisoning particularly in dogs, diabetes mellitus in cats, hyperthyroidism in cats, malignant lymphoma and ingestion of red maple leaves in the horse.
Blood grouping
Blood grouping of any animal is important in order to prevent potentially fatal transfusion reactions, and to avoid the development of antibodies which may arise as a result of an incompatible blood transfusion.
In general, dogs do not possess iso-antibodies to incompatible blood groups. Thus, they are generally able to tolerate an initial incompatible blood transfusion. However, incompatible transfusions should be avoided since antibodies resulting from a transfusion of incompatible blood may form in only five to seven days, and will have a long-term viability, eliminating the option of using incompatible blood in a future emergency situation. DEA 1.1 and DEA 1.2 are the most significant antigens in the dog. Both are highly antigenic, but DEA 1.1 is the primary lytic factor in canine transfusion medicine. Axiom veterinary laboratories test for DEA 1.1 blood group only.
In cats one blood-group system consisting of two antigens expressed either alone or in combination has been described: type A ,type B, and type AB. These antigens are unrelated to the ABO antigens found in humans and are defined by feline alloimmune sera.
Fibrinogen
Fibrinogen is a glycoprotein primarily concerned with haemostasis; it serves as the substrate for thrombin in the formation of fibrin.
Age, sex, exercise, repeated bleeding, or haemorrhage does not appreciably affect plasma fibrinogen concentrations, but they can be altered by only moderately inflammatory states. Fibrinogen behaves as an acute phase protein in most species, including birds. Therefore, its plasma concentration usually increases in inflammatory, suppurative, traumatic and neoplastic conditions. This is because of increased synthesis by hepatocytes and tumour necrosis factors.
Hyperfibrinogenemia is a better indicator of inflammatory disease in cattle than neutrophilia, because it is encountered more frequently.
The Prothrombin time (PT)
The prothrombin time measures the extrinsic pathway (ie, factors I, II, V, VII and X).
The prothrombin time (PT) may be used in cases of suspected warfarin poisoning and if warfarin is present, the PT will be prolonged.
An abnormal PT may also be found in patients with DIC, liver disease, or deficiencies of factors VII and fibrinogen.
The Activated Partial Thromboplastin time (APTT)
The APTT measures the intrinsic factor pathway (factors II, V, VIII, IX, X, XI and XII).
The APTT in conjunction with the PT measures a significant proportion of the coagulation system.
The D-Dimer assay
D-Dimer moieties are formed by plasmin degradation of Factor VIIIa cross-linked fibrin. Elevated levels are found in thromboembolic disease and disseminated intravascular coagulation.
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