2 - hematology techniques and analyzers

Question 1

what are the parameters measured in a complete blood count (CBC)

Answer 1

Erythrocyte parameters
- hematocrit, hemoglobin, RBC count
- erythrocyte indices: MCV, MCH, MCHC and sometimes RDW

leukocyte counts
- total leukocyte counts
differential leukocyte counts

platelets
- platelet count
- sometimes platelet volume (MPV)

Question 2

what is the electrical impedance method/instrument

Answer 2

obtains the count and size of cells
- by detecting the change in resistance proportional to to cell volume
- can determine the size difference btwn PLT and RBCs in most species
- cat platelets cannot be counted with this machine

• HCT, RBC, Hb, MCV, MCH, MCHC, and RDW are reported
• total WBC counts and generally platelet counts are reported

Question 3

why can cats platelets not be counted with an impedance machine

Answer 3

• cats have very large platelets compared to most species
• cat platelets are also more prone to clumping and being detected at something bigger like a RBC

Question 4

what are the cons of the impedience method

Answer 4

-** cannot determine intracellular characteristics of cells

-** cannot do platelet counts accurately in cats **

• **only 3-part differential based on cell size alone (limited accuracy) **

-** cannot preform reticulocyte counts **

Question 5

what is a laser flow cytometry machine

Answer 5

Determines the number, size and internal complexity of cells

-forward scatter reads cell size. shadow is related to the size
- side scatter reports what is inside the cell
- also has the ability to read labeled (florescent stained) cells like reticulocytes

• total WBC and 5 part differential counts (basophils are not accurate in dogs)
• **can obtain a reticulocyte count **

Question 6

what does side scatter do

Answer 6

it is a measure of the cells internal complexity or granularity

• neutrophils, with their multilobed nucleus and granules have high amounts of side scatter
• lymphocytes have lower levels of scatter

Question 7

what does RBC count parameter provide

Answer 7

little value by itself
- used to calculate Hct electronically. MCV and MCH manually

Question 8

how is PCV and Hct determined

Answer 8

centrifugation = packed cell volume (PCV)

• automated cell counters calculate the hematocrit (Hct) from the MCV and RBC count

Hct% = MCV x RBC /10

Question 9

how is hemoglobin determined

Answer 9

by spectrophotometric assay
- sodium lauryl sulfate (SLS) reagent is used to lysis the cells and turn it into a stable methemoglobin product

Can get falsely elevated values if the sample is cloudy
- lipemia
- Heinz bodies

Question 10

what are the erythrocyte indices

Answer 10

MCV: mean cell volume

MCH: mean cell hemoglobin (not very useful)

MCHC: mean cell hemoglobin concentration

RDW: red cell distribution width

Question 11

what is MCV

Answer 11

Mean cell volume
- measured in femtoliters (fL = 10^-15 liter)
-avg volume of a single erythrocyte
- determined directly in hematology analyzers

Question 12

what is MCH

Answer 12

Mean cell hemoglobin
- avg amount of hemoglobin in a single erythrocyte (picogram)

• generally correlated
  directly with changes in erythrocyte size (MCV)
• lowest values are reported in severe iron deficiency anemia (low MCV and low internal hemoglobin conc.)

Question 13

what is MCHC %

Answer 13

Mean cell hemoglobin concentration
- **reported as g/dL of packed erythrocytes/rbcs (NOT whole blood) **

Question 14

what is RDW

Answer 14

Red cell distribution width
- coefficient variation of erythrocyte volumes and an **electronic measure of anisocytosis **

Question 15

low MCHC % photo

Question 16

what is anisocytosis

Answer 16

Size variation
- big difference in size of the RBCs

Question 17

why can you have spuriously increased RDW

Answer 17

• erythrocyte agglutination
• platelets counted in erythrocyte histogram of severely anemic patients

Question 18

what are reticulocyte counts

Answer 18

• absolute reticulocyte counts are determined by flow cytometry must be validated using manual counts
• verify which reticulocytes are counted in cats. **Only aggregate reticulocytes are counted in most instruments **

Question 19

what causes spurious reticulocytosis

Answer 19

• erythrocyte parasites containing RNA and DNA (hemotropic mycoplasmas, babesia)
• howell-jolly bodies (micronuclei)
• nucleate erythrocytes
• large immature platelets or platelet clumps
• Heinz bodies with nonspecific fluorescence
• autofluorescence (drugs, porphyrin)
• leukocytosis - uncommon

Question 20

what can cause false platelet counts

Answer 20

**Platelet aggregates (clumps) can result in false thrombocytopenia
- platelet activation during blood collection and handling (especially in cats)

verify platelet counts, esp thrombocytopenia by stained blood film examination

Question 21

what is the MPV

Answer 21

mean platelet volume
- is the avg volume of a single platelet

Question 22

what causes spuriously increased MPV

Answer 22

• platelet aggregates
• storage of blood at 5C

Question 23

what are some errors in blood cell measurement

Answer 23

nucleated erythrocytes in blood
- counted as leukocytes by manual and most automated cell counters
- **calculate corrected total leukocyte count before calculating absolute differential leukocyte counts **

Question 24

photos to add
- MCHC %
- anisocytosis cells
- Dot plot example
- cat agger retics