2 - hematology techniques and analyzers Flashcards
what are the parameters measured in a complete blood count (CBC)
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)
what is the electrical impedance method/instrument
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
why can cats platelets not be counted with an impedance machine
- 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
what are the cons of the impedience method
-** 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 **
what is a laser flow cytometry machine
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 **
what does side scatter do
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
what does RBC count parameter provide
little value by itself
- used to calculate Hct electronically. MCV and MCH manually
how is PCV and Hct determined
centrifugation = packed cell volume (PCV)
- automated cell counters calculate the hematocrit (Hct) from the MCV and RBC count
Hct% = MCV x RBC /10
how is hemoglobin determined
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
what are the erythrocyte indices
MCV: mean cell volume
MCH: mean cell hemoglobin (not very useful)
MCHC: mean cell hemoglobin concentration
RDW: red cell distribution width
what is MCV
Mean cell volume
- measured in femtoliters (fL = 10^-15 liter)
-avg volume of a single erythrocyte
- determined directly in hematology analyzers
what is MCH
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.)
what is MCHC %
Mean cell hemoglobin concentration
- **reported as g/dL of packed erythrocytes/rbcs (NOT whole blood) **
what is RDW
Red cell distribution width
- coefficient variation of erythrocyte volumes and an **electronic measure of anisocytosis **
low MCHC % photo
what is anisocytosis
Size variation
- big difference in size of the RBCs
why can you have spuriously increased RDW
- erythrocyte agglutination
- platelets counted in erythrocyte histogram of severely anemic patients
what are reticulocyte counts
- 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 **
what causes spurious reticulocytosis
- 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
what can cause false platelet counts
**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
what is the MPV
mean platelet volume
- is the avg volume of a single platelet
what causes spuriously increased MPV
- platelet aggregates
- storage of blood at 5C
what are some errors in blood cell measurement
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 **
photos to add
- MCHC %
- anisocytosis cells
- Dot plot example
- cat agger retics
