Blood analysis - CAR Y1 Vet med

what do we use a haemocytometer for?

• RBC count

what do we use a microhaematocrit for?

• % RBCs by volume of total blood

what do we use blood smears for?

• microscopic examination

why do we use blood smears often?

• no computer error

• can see the shape of the cells

what are 4 automated blood sampling methods?

• automated analysers

• coulter principle

• laser cell counters

• quantitative buffy coat analysis

Outline microhaematocrits:

1. what are they used for

2. what are their advantages?

1. measures volume occupied by RBCS: volume of the whole blood = PCV

2. rapid and cheep in house test - gives a large amount of information

what is PCV

• packed cell volume

What are the 3 layers in a normal haematocrit and what do each of these examples represent?

1. red = erythrocyte layer middle layer = buffy coat top = should be plasma

2. 1. normal

3. 2. dehydration

4. 3. billirubinaemia (jaundice)
   4. haemolysis

5. 5. lipaemia

6. 6. leukocytosis/thrombocytosis

what may cause a dehydrated haematocrit sample?

• artefacts of stored blood

• swelling of RBCs

What are automated cell counters?

How do they work?

• a coulter principle (electrical technique) that enumerates and identifies blood cell populations

• stream of cells passes through an aperture b/w 2 chambers, across which there’s an electrical current.

  • passing cells disrupt electrical flow → pulse

what is amplitude proportional to in an automated cell counter and what about pulse frequency?

1. cell volume

2. cell number

what is absorbance used for in automated cell counters

• haemoglobin

What are the measured values for:

1. RBCs

2. MCV (mean corpuscular volume)
   Platelets

3. WBCs

4. Haemoglobin

1. absolute number per litre

2. average volume of rbcs (fl)

3. absolute number per litre

4. absolute number per litre

5. amount in blood: g/l

How do we calculate haematocrit

• Hct = PCV (packed cell volume)

calculation =

hct/PCV = (MCV x RBC count)/100

what is MCH and how do we calculate it?

• mean corpuscular haemoglobin = average amount of Hb per rbc, in picograms

calculation:

MCH pg = Hb x 10 / RBC count

what is MCHC and how do we calculate it?

• mean corpuscular Hb concentration = average concentration of Hb in the cells relative to their size/volume

calculation:

MCHC g/dl = Hb x 100/Hct

what are 4 limitations to automated systems?

1. don’t give reliable differential white cell counts

2. small RBCs may be undercounted and counted as platelets

3. Large platelets may be counted as RBCs

4. can’t ID RBC morphology, WBC morphology or blood parasites

what are 6 problems with blood samples?

1. correct tube selection - correct anti-coagulant for the test required

2. clotting

3. haemolysis

4. appropriate tube fill

5. lipaemia

6. labelling - species!

What can we assess in blood smears? What further step can we take and why?

1. differential leukocyte count - diversity of leucocyte pattern

2. morphology of cells

3. presence of abnormal cells/parasites

4. platelet counts - manual estimate to confirm automatic analysis

   send w. EDTA sample for analysis → distinguish b/w ‘sample ageing’ and genuine diagnostic findings

what is erythrocyte sedimentation rate

• see how long it takes a sample to start sedimenting

what can we analyse from sedimentation rate?

• increase is a non-specific change in many diseases

  • probably due to plasma changes that encourages coagulation

• larger aggregates sediment more quickly

what should the sedimentation rate be in:

1. dogs

2. pigs

3. what happens to that rate during disease

4. does it increase for horses/ruminants? what does that indicate?

1. dogs = 5-10mm/h

2. pigs = 2-14mm/h

3. increases (can be more than 10 x more)

4. ESR too high in HORSES = due to disease, DOESN’T increase due to ruminants

what is TIBC

• total iron binding capacity

• it’s an indirect measure of the amount of transferrin in the blood

what is anaemia

• a condition in which the capacity of blood to transport O2 is reduced

what can results in anaemia

1. reduced number of circulating rbcs

2. reduced Hb per erythrocyte

3. both

what are the 3 basic variables of anaemia?

• total Hb

• PCV or haematocrit

• RBC count

is anaemia a diagnosis?

• NO

• it’s a clinical observation/finding

what are 5 causes of loss of blood

• internal bleeding due to clotting disorder

• bleeding intestinal neoplasm/ulcer

• severe hookworm infections

• trauma

• severe flea infestation

what are 3 causes of lysis of erythrocytes

1. transfusion reaction

2. bacterial infections e.g. Mycoplasma haemophilis

3. neonatal erythrolysis

what are 5 causes of reduced erythropoiesis

• viral diseases

• lymphoma/leukaemia

• lead poisoning

• iron deficiency

• chronic renal disease

how do we characterise anaemia on rbc morphology:

1. too high

2. normal

3. too low

1. macrocytic

2. normocytic

3. microcytic

how do we characterise anaemia on Hb content:

1. too low

2. normal

3. too high?

1. hypochromic

2. normochromic

3. technically hyperchromic BUT - the max amount of Hb is in an erythrocyte, if something contains more than an rbc = AN ARTEFACT

how do we characterise anaemia on reticulocyte count and what does it indicate?

• regenerative or non-regenerative

• bone marrow response

how does renal disease/failure affect erythropoiesis?

• reduction in EPO

• reduced rate of erythropoiesis

what is the normal PCV in:

1. dog

2. cat

3. cow

4. horse

5. sheep

as a %?

1. 35-57

2. 30-45

3. 24-46

4. 27-43

5. 27-45

what is the TP (total protein) in g/dl for:

1. dog

2. cat

3. cow

4. horse

5. sheep

1. 5.4-7.5

2. 6.0-7.9

3. 5.6-7.6

4. 6.0-7.9

what may be a cause of an increased PCV and TP?

• dehydration

what may be a cause of an increased PCV and normal/decreased TP

• splenic contraction: polycythaemia or hypoproteinaemia

what may be a cause of normal PCV but an increased TP

• normal hydration with hyperproteinaemia, anaemia and dehydration

what may be a cause of decreased PCV and increased TP

• anaemia and dehydration

• anaemia w. hyperproteinaemia

what may be a cause of decreased PCV and normal TP

• non-blood loss anaemia with normal hydration

what may be a cause of normal PCV and normal TP

• normal

• acute haemorrhage

• dehydration and anaemia and hypoproteinaemia

what may be a cause of decreased PCV and TP?

• blood loss

• anaemia and hypoproteinaemia

• overhydration