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Regenerative and Non-Regenerative Anaemias (view source)
Revision as of 18:07, 7 March 2022
, 18:07, 7 March 2022no edit summary
===Haemorrhage===
===Haemorrhage===
This may be acute, transient severe haemorrhage or chronic, persistent haemorrhage. There may be evidence of blood loss, such as external haemorrhage from wounds, lesions or body orifices (nares, anus); may be associated signs of trauma (RTA) or possibly defective haemostasis. Internal haemorrhage may be intracavity or into the GI or urinary tract and evident in excreted material (urine, faeces, vomit). It can appear as fresh or altered blood. Small amounts of blood may not be visible to the naked eye but may be visualized microscopically or detected chemically.
Immediately following acute haemorrhage the PCV and other RBC indices remain relatively stable, whole blood has been lost and haemodilution, due to fluid shifts from the extravascular to the intravascular compartment, takes time to develop. Splenic contraction may also helpmaintain the PCV. After 2-3 hours, haemodilution becomes evident, leading to reductions in red cell indices and plasma protein concentrations. The full magnitude of blood loss may not be evident until 24hrs after the onset of haemorrhage. Red cell indices may be less affected following haemorrhage into body cavities because two thirds of the erythrocytes may return to the circulation; plasma proteins and iron from the remaining RBCs are retained and can be utilised for erythropoiesis. Anaemia is initially normocytic normochromic but after 2-4 days there is a significant erythroid response, which is most marked by day 7, and features polychromasia, reticulocytes, Howell-Jolly bodies, nucleated RBCs, increased MCV. If reticulocytosis and thrombocytosis, with reduced plasma proteins persist after 2-3 weeks, continuing haemorrhage should be suspected. PCV should have returned to low normal by 2 weeks following a single episode of haemorrhage.
By the time chronic haemorrhage causes clinical signs of anaemia, regeneration should have begun, The regenerative response is more marked with acute haemorrhage. With persistent chronic haemorrhage, particularly with blood loss from the body, the RBCs may be microcytic and hypochromic due to iron deficiency. There is initially an increased reticulocyte count which then falls as iron deficiency develops.
Even after haemorrhage the regenerative response may be poor or absent if the bone marrow is damaged or activity is suppressed by, for example, neoplasia or infection.
'''<u>Leucocyte changes</u>'''. Acute blood loss is usually accompanied by a leucocytosis with neutrophilia and a left shift (in- creased band cells). This is not associated with infection but may reflect inflammation secondary to hypoxic damage. Immediately post haemorrhage there may be a mild to moderate transient thrombocytopaenia due to increased platelet consumption; this is followed by thrombocytosis with large immature platelets, reflecting the bone marrow response to increased demand.
Chronic blood loss is often associated with thrombocytosis (platelet count 500-1000x109/l).
'''<u>Biochemical changes</u>'''. Plasma protein and albumin levels will be low after severe acute haemorrhage and may be low with chronic haemorrhage.
Increased blood urea nitrogen with normal serum creatinine can be seen with gastrointestinal haemorrhage.
References: [[/en.wikivet.net/NationWide Laboratories|NationWide Laboratories]]
Any form of spontaneous haemorrhage with no apparent cause may suggest the presence of an underlying coagulopathy. The most common haemorrhagic presentations are:
*'''Epistaxis''' due to disruption or erosion of blood vessels of the nasal cavity by trauma, neoplasia, fungal infection or a foreign body.
*'''Epistaxis''' due to disruption or erosion of blood vessels of the nasal cavity by trauma, neoplasia, fungal infection or a foreign body.
*'''Haematuria''' which may arise due to haemorrhage from any part of the urinary tract, especially the kidney (due to trauma, neoplasia or idiopathic haematuria) and bladder (due to trauma, cystitis, urolithiasis and neoplasia).
*'''Haematuria''' which may arise due to haemorrhage from any part of the urinary tract, especially the kidney (due to trauma, neoplasia or idiopathic haematuria) and bladder (due to trauma, cystitis, urolithiasis and neoplasia).
===Haemolysis===
===Haemolysis===
Usually presents as a markedly regenerative anaemia without hypoproteinaemia or other evidence of blood loss. Haemolysis may be intravascular or extravascular.
* Extravascular haemolysis relates to the pathological phagocytosis of erythrocytes by macrophages in spleen, liver and bone marrow and is the most common form of
haemolytic anaemia.
* Intravascular haemolysis relates to destruction of erythrocytes within the circulation and often results in more acute and severe haemolysis then extravascular haemolysis. Haemoglobinuria is often a feature. The most common causes are complement fixing immune-mediated haemolytic anaemia and Heinz body anaemia.
* When both forms occur together, the haemolysis is classified by the predominant type.
* Haemolytic anaemias often result in a degree of hyperbilirubinaemia which, if sufficiently severe, will be evident as icterus. RBC destruction leads to an increased level of unconjugated bilirubin which exceeds the rate of hepatic excretion. Acute severe anaemia may also cause hypoxic or toxic hepatic injury, resulting in decreased bilirubin metabolism and cholestasis. Although hyperbilirubinaemia results primarily from increased unconjugated bilirubin, conjugated bilirubin also increases and leads to bilirubinuria. Evaluation of unconjugated versus conjugated bilirubin is often not helpful when trying to differentiate between pre-hepatic and hepatic jaundice.
References: [[/en.wikivet.net/NationWide Laboratories|NationWide Laboratories]]
Haemolysis may occur in the following processes:
Haemolysis may occur in the following processes:
*'''Immune-mediated disease''' including [[Immune Mediated Haemolytic Anaemia]] and [[Neonatal Isoerythrolysis]].
*'''Immune-mediated disease''' including [[Immune Mediated Haemolytic Anaemia]] and [[Neonatal Isoerythrolysis]].