Red Cell Parameters Flashcards
What are the parts of a haematology report?
- eryhtron
- leukon
- thrombon
- morphology
What are we looking for when assessing red cells?
- Red cell mass (PCV/Hct, RBCC, Hgb)
- Evidence for effective and appropriate erythropoiesis (size and colour (MCV, MCHC) & reticulocyte count)
- Red cells size and variation (MCV, RDW)
- Red cell haemoglobinisation (colour) MCHC
- Red cell shapes and inclusions (Smear)
What is the difference between relative and absolute polycythaemia?
- Relative: Apparent increase in RBC due to a decrease in fluid in circulation (often increase in total protein and albumin)
- Absolute: True increase in RBC mass due to increased RBC production/release (usu polychromasia, anisocytosis and reticulocytes)
What do PCV, RBCC and Hgb measure?
Red cell mass and oxygen carrying capacity - usually increase and decrease in line with one another
Why can PCV be wrong?
- RBCs miscounted (mistaken for platelets or aggregated into pairs and triplets)
- MCV misleading (cell shrinkage or swelling during transport, tube filling or because of osmotic effects in machine)
How is PCV calculated?
PCV = MCV x RBCC
Why do we sometimes see high MCHC results?
- Not physiological to cram more Hgb into red cells than they will take
- Haemolysis (sample handling or intravascular)
- Lipaemia
Why are MCV results sometimes misleading?
- Swelling of transport
- Mis-identification – pairs and triplets, cross over with large platelets
- Cell shrinkage or expansion in sample e.g. hyperosmolar
- Will impact on calculated PCV/HCT
What is the rule of three?
Hct (%) approx. = Hgb (g/dL) x3 (+/- 3%)
How can we pick up rule of three error?
By looking up MCHC
What parameters is the classification of anaemia based on?
MCV and MCHC
What measures of anaemia are more sensisitve than MCV and MCHC?
Machine dot-plots and histograms more sensitive
What are the 3 common classes of anaemia?
- normocytic normochronic
- macrocytic hypochromic
- microcytic hypochromic
Which anaemia class is associated with a classic iron deficiency?
Microcytic Hypochromic
What effect on parameters does polycythaemia have?
Increase in PCV, Hgb concentration and RBC count
What are the signs associated with relative polycythaemia?
“Dehydration” (water or acellular fluid loss):
[eg vomiting, diarrhoea, polyuria, extensive burns, adipsia, water deprivation]
Exercise, fear, excitement, severe pain - stress: Adrenaline secretion, splenic contraction and transient redistribution of RBC from the spleen to the circulation
What parameters are affected by relative polycythaemia?
PCV is increased
No increase in RBC production
How is relative polycythaemia resolved?
Resolves after rehydration or removal of cause of splenic contraction
What parameter change is associated with absolute polycythaemia?
Increase in RBC production
What are the 2 types of absolute polycythaemia?
- primary
- secondary
What is primary polycythaemia?
- rare myeloproliferative disorder
- abnormal response of RBC precursors
- Normal EPO levels
What is associated with secondary polycythaemia?
- Chronic tissue hypoxia of renal tissues (low arterial pO2) due to:
heart/lung diseases, high altitude, thrombosis, constriction of renal vessels - Renal tumor or cysts [↑intra-capsular pressure]
- Increased EPO
What are reticulocytes?
Young (immature/non-nucleated) erythrocytes prematurely released to blood from the bone marrow in regenerative anaemias
Why would we measure reticulocyte count?
- Evaluation of erythropoiesis in bone marrow.
- Differentiation of regenerative and non-regenerative anaemia.
What do reticulocytes look like on romanowsky (routine) stain?
have “polychromatophil” appearance
How are reticulocytes counted?
- manual
- automated (analysers)
What is the absolute reticulocyte count?
observed % reticulocytes x RBC x 10
What is a normal reticulocyte count in dogs?
Low number of reticulocytes (<1%)
Expect at least (>60x109/L) in regenerative anaemias
What is a normal reticulocyte count in cats?
Low number of reticulocytes (0.2-1.6%)
Expect at least (>50x109/L) in regenerative anaemia
What are the 2 kinds of reticulocytes in cats?
‘aggregate’ blue stained coarse clumping (0.5% of erythrocytes)
‘punctate’ small, blue stained dots (1-10%).
Kinetics of Aggregate vs Punctate means we only consider Aggregate in assessment of regeneration
What is the normal count of reticulocytes in ruminants and horses?
- Virtually no reticulocytes in normal blood;
- Reticulocytes may not appear even in very severe anaemias in horses;
- In cattle peak production 7-14 days post acute blood loss
What species variation is there in RBCs volume?
What species variation is there in RBC number?
Which species is this blood slide typical of? why?
Dog
* Larger erythrocytes
* Uniform size
* Central pallor
What species is this blood slide typical of? why?
cat
* Smaller erythrocytes
* Anisocytosis (variation in size)
* Scarce central pallor (less concave)
What species is this blood slide typical of? why?
Ruminant
Anisocytosis and crenation
What species is this blood slide typical of? why?
Horse
Rouleaux
(sedimentation tendency)
What variations are there in RBCs within dog breeds?
- macrocytosis in some poodles
- akitas have unusually small erythrocytes and particularly high potassium content
- greyhounds have high PCVs (0.55-0.6 L/L)
What is poikilocytosis?
Variation in cell shape
What can cause alteration in cell shape in RBCs?
abnormal erythropoeisis
specific organ dysfunction
What are codocytes?
mexican hat cells - important in Fe deficiciency
What are spherocytes?
Important in diagnosing IMHA
What are acanthocytes?
Thorny spikey cells
Few irregular elongations of RBC border with rounded ends
What are schistocytes?
Erythrocyte fragmentation
What are echinocytes?
Small little even spikes along the outside
What inclusions might we see in RBCs?
- Howell Jolly bodies (nuclear remnant)
- Basophilic stippling
- Nucleated RBC’s
- Infectious agents (Mycoplasma, Babesia, Viral inclusions)
- Heinz bodies (crystallised haemoglobin)
What are rouleaux formations?
- Clustering, sticky, piling of RBCs
- Normal finding in horses
- Indicates inflammation in small animals
- Relates to increased “stickiness” of plasma with increased globulin content
What causes agglutination of RBCs?
- IMHA
- mismatched blood transfusion
How to we differ rouleaux formation from agglutination?
To confirm agglutination:
Mix 1 drop of blood with 1 drop of saline
-> Agglutination will persist, rouleaux formation will disperse
