References
Poisons affecting the blood
Abstract
Blood circulates as a liquid containing cells and numerous chemicals; it functions to transport nutrients, chemicals, oxygen and waste products to and from cells, and is involved in defence and wound repair to tissues. Numerous toxic substances can disrupt the normal function of the blood through various mechanisms resulting in clinical signs of poisoning. Some of the substances that commonly cause adverse effects on the blood in companion animals are described. These include onions and related food plants which cause oxidative damage to red blood cells and the formation of Heinz bodies, and zinc which causes haemolytic anaemia. Haemoglobin is also subject to oxidative damage from paracetamol metabolites resulting in the formation of methaemoglobin which is non-functioning, resulting in tissue hypoxia. Disruption of the clotting cascade by anticoagulant rodenticides results in delayed-onset haemorrhage and the drug 5-fluorouracil disrupts the formation of blood cells causing bone marrow depression.
Blood is a fluid that transports nutrients, oxygen and waste products to and from cells. It is also involved in defence and wound repair. Blood contains red blood cells, various types of white blood cells and platelets suspended in plasma. The red colour of vertebrate blood is due to haemoglobin, a protein in red blood cells, that is responsible for oxygen transport. Various poisons can affect the blood and produce a variety of biochemical changes and clinical signs. This article will discuss some substances that commonly cause adverse effects on the blood in companion animals.
Anaemia is a reduced number of red blood cells or haemoglobin in the blood and there are three main causes, blood loss (from trauma, for example), decreased red blood cell production or increased red blood cell breakdown. There is constant production of new, and removal of aged, red blood cells from the circulation. The normal lifespan of red blood cells is 110–120 days in dogs and 65–76 days in cats. It is also important that red blood cells are able to deform and squeeze through narrow capillaries. If they are damaged in some way and unable to deform, they will be removed from the circulation by the recticuloendothelial system (Lincoln et al, 1992).
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