Changes

==Clinical Significance==

==Clinical Significance==

'''Reductions''' in PCV are synonymous with [[Anaemia - Introduction|anaemia]] and they occur most commonly with haemorrhage, haemolysis or failures in the erythroid lineage.  In cases of acute haemorrhage, the PCV will not fall immediately because blood cells are lost in the same proportion as the aqueous solvent.  The osmotic movement of fluid from the interstitial space results in haemodilution and subsequent reduction of the PCV.

'''Reductions''' in PCV are synonymous with [[Regenerative and Non-Regenerative Anaemias|anaemia]] and they occur most commonly with haemorrhage, haemolysis or failures in the erythroid lineage.  In cases of acute haemorrhage, the PCV will not fall immediately because blood cells are lost in the same proportion as the aqueous solvent.  The osmotic movement of fluid from the interstitial space results in haemodilution and subsequent reduction of the PCV.

'''Increases''' in PCV usually occur in dehydrated animals in which the blood cells come to occupy a greater proportion of the blood volume, a process called '''haemoconcentration''' or '''relative polycythaemia'''.  Other reasons for increases in PCV include:

'''Increases''' in PCV usually occur in dehydrated animals in which the blood cells come to occupy a greater proportion of the blood volume, a process called '''haemoconcentration''' or '''relative polycythaemia'''.  Other reasons for increases in PCV include:

*'''Secondary absolute polycythaemia''' which may be caused by the paraneoplastic production of erythropoietin (EPO) from renal tumours or it may occur as a response to the hypoxygenation of blood in animals with reverse-shunting [[PDA|patent ductus arteriosus]] (PDA) or [[Tetralogy of Fallot]].  

*'''Secondary absolute polycythaemia''' which may be caused by the paraneoplastic production of erythropoietin (EPO) from renal tumours or it may occur as a response to the hypoxygenation of blood in animals with reverse-shunting [[PDA|patent ductus arteriosus]] (PDA) or [[Tetralogy of Fallot]].  

Since PCV is not a measure of the actual number of red blood cells, anaemic animals may appear to have a normal or even increased PCV if they also become dehydrated.  An example of this phenomenon occurs with [[Hypoadrenocorticism|Addison's disease]], where animals frequently have a non-regenerative anaemia which is masked by dehydration in an Addisonian crisis.

Since PCV is not a measure of the actual number of red blood cells, anaemic animals may appear to have a normal or even increased PCV if they also become dehydrated.  An example of this phenomenon occurs with [[Hypoadrenocorticism|Addison's disease]], where animals frequently have a non-regenerative anaemia which is masked by dehydration in an Addisonian crisis.

==Literature Search==

==Literature Search==