10.4HAEMATOLOGY 10.4 HAEMATOLOGY

The purpose of conducting a haematological screen is to identify abnorparameters such as packed cell volume (PCV) or haemoglobin conincreased or reduced red or white cell numbers, altered red or white blood cell morphology, or an abnormal platelet count that may indicate the presence of disorders such as:


(1) anaemia
(2) dehydration
(3) myeloproliferative disorders
(4) immunosuppression
(5) infection.


Packed cell volume (PCV, haematocrit index)


Cat Normal range: 0.30-0.45 l/l (30-45%)

Dog Normal range: 0.37-0.66 l/l (48-66%)


A low PCV indicates the presence of anaemia with consequential reducin oxygen carrying capacity in the blood - which may be particularly harmful in older animals in which tissues may be particularly sensitive to local hypoxia.

A high PCV usually indicates the presence of dehydration. Many authors consider that older animals are in a state of relative dehydration -and this is certainly likely in the presence of polyuric syndromes such as diabetes, renal failure and hyperadrenocorticism.



Red blood cell count

Cat Normal range: 5-10 x 1012/1
Dog Normal range: 5.5-9.5 x 1012/l


Low red blood cell (erythrocyte) numbers usually indicates the presence of anaemia. High red cell counts usually indicate the presence of dehydration - and only occasionally true polycythaemia.



Haemoglobin

Cat Normal range: 8-15 g/dl
Dog Normal range: 12-23 g/dl


High haemoglobin concentrations usually indicate the presence of dehyand occasionally polycythaemia~

Low haemoglobin concentrations usually indicate the presence of anaemia.



Mean corpuscular volume (MCV)

Cat Normal range: 39-55 fl
Dog Normal range: 60-77 fl


High MCV values may be caused by abnormally large, immature eryand is seen in regenerative anaemia (see below), myeloprolidisorders, and rarely in macrocytic anaemia.

About 50% of cats with hyperthyroidism may have a high MCV. Low MCV values are seen when red cell size is small such as is caused by chronic haemorrhage and occasionally iron deficiency or feline haemo



Mean corpuscular haemoglobin concentration (MVHC)

Cat Normal range: 30-36 g/dl
Dog Normal range: 32-36 g/dl


Low MCHC values are seen with hypochromic cells (due to iron deficiency secondary to chronic inflammatory disease, chronic infection and neo-plasia), and in regenerative anaemia. Protein-losing conditions may also lead to protein deficiency and low MCHC values.



Erythrocyte sedimentation rate (ESR)

Has to be corrected according to PCV measurement (see Bush 1991)

Cat Normal range: 0-12 mm/h
Dog Normal range: 0-5 mm/h


A high ESRr is seen in acute generalised infections (e.g. endocarditid), inflammatory diseases (e.g. peritonitis, pericarditis and pleuritis), rheumatoid arthritis, chronic pyometra, malignant neoplasia, renal failure, hypoproteinaemia, hypothryroidism, hyperadrenocorticism.

A low ESR (negative after correction for PCV) is seen in haemolytic anaemia.

Many of the red cell abnormalities reported will indicate the presence of anaemia and it is important to attempt to interpret the results accuractely (Table 10.3)


Regenerative anaemia (responsive as evidencied by the production of reticulocyts which are released into circulation) occurss after haemorrhage or haemolysis. Non-regenerative anaemia is commonly associated with thrombocytopenia and myeloproliferative disease (Table 10.4)

Platlet Count

Cat Normal range: 300-700 x 109/l
Dog Normal range: 200-500 x 109/l


Animals with obvious clinical signs of haemorrhage or with a regenerative anaemia on routine screening should have their platelet count monitored. However it is a useful examination to include in a routine screen because of the number of chronic, subclinical conditions which can affect circuplatelets.


A reduced number of platelets (thrombocytopenia) occurs due to decreased production, increased destruction or loss from the body circuand is seen in bone marrow disease, uraemia, toxaemia, infection, hypoadrenocortidsm, DIC, immune-mediated disorders, myeloproliferadisorders, haemorrhage and splenomegaly.

An increased number of platelets (thrombocytosis) occurs due to excessive production rate or decreased removal from the circulation and is seen in postsplenectomy, in acute or chronic infections, inflammatory

disease, drug induced, some myeloproliferative disorders (most cause thrombocytopenia) or malignant neoplasia.



Abnormal red cell morphology

White blood cell count

Differential white cell count

Abnormal white cell morphology