Anaemia Notes

Anaemia

1. Introduction

Anaemia is a common clinical presentation, but is not a diagnosis itself.

Anaemia is defined as a situation in which the total erythron mass in peripheral blood is depleted below reference values. The three basic variables of erythron that determine whether an animal is anaemic are:

• Haemoglobin

• Packed cell volume (PCV) or haematocrit

• Red blood cell count

Red blood cell count is the least accurate of these measures. Haemoglobin concentration will be falsely high in lipaemic samples. Dehydrated animals will have a contracted plasma volume and so an increased PCV – this could mean the animal has a masked anaemia.

Anaemia can be classed as regenerative or not regenerative. The causes of both types of anaemia are as follows:

There will be some normal variation between individuals and reference ranges, such as:

• Certain breeds have naturally lower PCV – poodles and greyhounds.

• Medication such as sedation and anaesthesia may decrease PCV.

• Pregnancy will decrease red blood cell count, PCV and haemoglobin.

• Stress or excitement will increase PCV, haemoglobin and red blood cell count.

• Puppies under 6 months old have a lower red blood cell count, haemoglobin and PCV.

Clinical signs of anaemia include:

• Signs of inadequate tissue oxygenation

• Pale mucous membranes

• Exercise intolerance, weakness, lethargy, inappetance or anorexia.

• Signs of compensatory mechanisms

• Tachypnoea or dyspnoea

• Tachycardia, rapid weak pulse, heart murmur

• Other potential signs

• Icterus, haemorrhage, melena, haematuria

• Pain, pica (cats)

• Spleno or hepatomegaly, lymphadenopathy

The severity of clinical signs reflects the chronicity of anaemia, not the degree of anaemia. Guidelines for interpreting severity of anaemia are as follows:

Microhaematocrit is an accurate measure of PCV.

2. Variables that characterise anaemia

Variables that characterise anaemia include:

• The regenerative response, i.e. reticulocyte count.

• Red cell indices such as mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentration (MCHC).

• Red cell morphology on blood smear.

  1. The regenerative response

The greatest regenerative responses are seen with haemolytic anaemia (6-8 fold increase) and with haemorrhagic anaemia (2-4 fold increase). However, red cell production takes 4 days. Therefore pre-regenerative conditions may exist up to 4 days after haemolysis or haemorrhage.

An absence of reticulocytes in an ongoing anaemia indicates a defect in production.

2. Red cell indices

Red cell indices define the quality of red cells produced by describing red cell size (MCV) and average cell haemoglobin content (MCHC).

In a very regenerative response, a macrocytic (high MCV) hypochromic (low MCHC) population of red cells is expected.

Microcytic (low MCV) hypochromic (low MCHC) are likely to occur in conditions of defective haemoglobin synthesis such as iron deficiency.

Macrocytosis may also be seen in myelodysplasia in cats, in association with the administration of antiepileptic drugs and rarely in some Poodles as a dyscrasia.

Microcytosis may be seen normally in the Japanese Akita and Shiba Inu breeds and in some dogs with portosystemic shunts.

3. Red cell morphology

Red cell morphology is evaluated by examination of a stained blood smear.

3. Regenerative anaemia

Features of regenerative anaemia include:

• Reticulocytosis

• Anisocytosis

• Poikilocytosis

• Normoblastosis

• Basophilic stripping

• Increased Howell Jolly bodies

• Increase Heinz bodies

Causes of regenerative anaemia include haemorrhage, haemolysis and oxidative injury.

1. Haemorrhage

Blood loos by haemorrhage may occur by

• External blood loss

• Internal haemorrhage – blood loss into body cavity

• Coagulopathy

• Endoparasites

• GI blood...

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