Automated CBC Analysis Flashcards
Why perform automated evaluation of erythron?
- takes measure of animal’s ability to oxygenate tissues
- may give clues to underlying disease(s)
- hels assess need for care 🡒 supp. O2, IV fluid, transfusion, etc.
- expands findings of peripheral blood smear
Sample type for CBC
anticoagulated whole blood sample
Most mammals = potassium EDTA tube (purple/lavender top tube)
Horses + exotics (pocket pets, avian, reptiles, etc) = lithium or sodium heparin tube (green top tube)
Limitations of Hematology Analyzers
Unable to detect:
- blood parasites
- most RBC shape changes
- toxic changes within neutrophils
Imperfect decision of:
- nRBCs
- immature or neoplastic WBCs
- specific leukocyte types for differential count
- platelet count of samples with platelet clumps
Hematocrit (%)
normal blood is ~55% plasma + 45% cells (mostly RBCs)
calculated value on many automated analyzers = indirect measurement
usually equivalent to spun PCV = direct measurement
RBC Count
expressed as millions of cells per/uL (x10^6/uL)
individualized RBCs counted by detecting light scatter from RBCs as they pass thru laser machine or by breaking an electrical current
automated RBC counts not yet possible in species with nucleated RBCs
Hemoglobin Concentration (g/dL)
Hgb content within aliquot of blood
false 🡑 by:
- heinz bodies
- hemolysis
- lipemia
Hgb x 3 = Hct +/- 3%
- used to double check mahcine Hgb + Hct values
- Hgb should be ~1/3 the Hct when RBCs are of normal size
If they don’t match = spin a PCV
- if Hct differs from spun PCV, PCV considered more accurate
- if Hct equivalent to spun PCV, Hgb result is suspent
Changes in RBC count, Hgb +/or Hct
- these values collectively reflect erythrocyte mass of patient
- generally 🡑/🡓 together
sometimes 1-2 analytes will be ouside their respective RI
Causes:
- Hgb impacted by hemolysis, lipemia, heinz bodies
- RBC population in flux
- concurrent changes in RBC size + Hgb content of cells
- miscounting of RBCs by analyzer
🡓 in RBC count, Hgb +/or Hct
**typically indicates anemia **
- however consider hydration status
- true severity of anemia is masked by dehydration
other causes:
- dilution
- miscounting of small RBCs
- RBC clumping 🡒 miscounting
🡑 in RBC count +/or Hct
- called erythrocytosis
- frequently due to dehydration
MCV
Mean Cell Volume (MCV) of an average RBC
measured directly by most analyzers but can be calculated
normocytic = descriptive term to mean MCV within RI
- mean + RI vary by species
🡑 MCV
Macrocytic/macrocytosis
most commonly d/t 🡑 # of circulating reticulocytes/polychromatophils
- in patients w/ active erythropoiesis
- often anemic patient with BM that is responding to problem
- may be only hint of regeneration in anemic horse
Other causes:
- in vitro RBC swelling d/t sample age (>24 hrs)
- RBC agglutination
- FeLV+ cats
- sighthounds
- uncommon breed anomalies
🡓 MCV
microcytic/microcytosis
iron deficiency = most common cause
- often d/t chronic hemorrhage
animals with significant liver disease or vascular anomalities
reported in several east asian dog breeds
may be seen in neonates of most species
MCH + MCHC
Mean Cell Hemoglobin (MCH)
- mean amount of Hgb in an avg RBC
- calculated value using RBC count
Mean Cell Hemoglobin Concentration
- mean amount of Hgb in an avg RBC
- calculated value that uses Hct
MCHC considered more reliable
- bc we can readily verify Hct using PCV when Hgb + HCt don’t match
- we can’t easily verify RBC count
🡑 MCH/MCHC
hyperchromic/hyperchromasia
RBCs don’t make too much Hgb so 🡑 in this should get your attention
analyzer assumes all Hgb present is within cell:
- pathology = heinz bodies read as a higher conc. of Hgb
- artifact = EC hgb from hemolysis + lipid mol. from lipemia also read as IC hgb
🡓 MCH/MCHC
hypochromic/hypochromasia
Causes:
1) many circulating reticulocytes/polychromatophils
- lower conc. of Hgb in immature RBCs
- often seen in patients w/ regenerative anemia
- polychromasia on blood film exam
- reticulocytosis on NMB stain
2) iron deficiency anemia
- not enough iron in body to fully stock RBCs with Hgb
analyzer may detect mild hypochromasia without visually appreciable decrease in cytoplasmic color on blood smear
Quantification of Reticulocytes
2 methods of quantification:
1) automated count via flow cytometry w/ certain hematology analyzers
2) manual count of # of reticulocytes out of 1000 total RBCs performed on blood film stained with NMB = %
reticulocytes counts using either method are important for accurate assessment of BM response to anemia for most species
in most species, we expect 🡑 # of circulating reticulocytes in regenerative anemia
