CBC basics

  1. MCV
    mean corpuscular volume
  2. MCH
    mean corpuscular hemoglobin
  3. WBC count
    • a gross count of every cell in a blood sample that is not red, regardless of it's cell type
    • *while WBC count generally points to infection, a high WBC doesn't necessarily mean infection nor does low WBC ensure there isn't one
  4. What noninfectious factors can raise WBC
    • examples:
    • AE of meds
    • trauma
    • air pollution
    • mental stress
  5. what is a differenctial
    • not a part of standard CBC
    • provides more detailed analysis of types of cells that make up whole WBC
    • depending on which cell counts are raised, neutral, or lowered, it can help id source of abnormal reading
  6. RBC component
    • more than one type is included
    • RBC typing is a factor of age, NOT lineage or function
    • Some belong to reticulocytes
    • *When total RBC, both young & old, is below 4.5 million for men and 4 million for women, criterion for anemia is met
  7. reticulocytes
    • young RBC released into bloodstream within last 48 hrs
    • ID by size and presence of proteins not found on mature RBC's
    • normally released into bloodstream at same rate old RBC's destroyed (about 1% of total RBC component per day)
  8. Hgb
    • Hgb is component of RBC which transports gases that the lungs exchange
    • Hgb value is weight measure of how much Hgb in grams is in 100 mL
    • Lab value less than 14 g for men, 12 g for women, is considered anemic
    • *Since Hgb is 1/3 of total volume of all RBC, can be approx by dividing Hct by 3. If ration doesn't reflect this, good idea to repeat CBC (unless bit by rattler)
  9. What is Hct?
    • A test tube of blood, when centrifuged, will separate into a red sediment (primarily RBC) in the bottom, with clear plasma above it
    • The volume of red sediment relative to the total sample volume is the Hct.
    • Example: if a test tube has 3 cm RBC sediment and 7 cm of plasma, Hct is 30%
  10. What does Hct mean
    • reflects interplay of 3 variables: fluid volume, RBC count, and RBC size
    • Any of these variables alone is enough to shift the Hct
  11. How can Hct evaluate pt fluid status?
    • If fluid is added to a test tube, as if sample was drawn from pt w fluid overload, the sediment volume % would decrease, lowering Hct.
    • Conversely, removing fluid from test tube, as if sample was drawn from dehydrated pt, would rise Hct.
    • In both cases, the absolute # or size of RBC remains unchanged; only fluid is manipulated
  12. How can altering sediment volume while holding fluid volume constant show change in Hct
    • One obvious way is to remove RBC, as in blood loss
    • *when using Hct to evaluate bleeding, important to remember during acute hemorrhage, the Hct goes up, not down.
    • The fall, often consider a marker of hemorrhage, is actually a delayed response that may take hours to appear.
    • This is due to vasoconstriction (a compensatory mech for acute hemorrhage) is the source of this deception, making Hct an unreliable indicator of acute bleed
  13. How can change in size of RBC, while holding fluid volume & RBC count steady, change Hct?
    • *A collection of many small RBCs can have the same volume (and same Hct) as fewer, larger ones.
    • A good example of shifting Hct by manipulating RBC size occurs in diabetic pt.
    • If one pours glucose into test tube, simulating diabetic hyperglycemia, the red sediment will swell up, raising the Hct.
    • This happens because glucose is transported into RBC's against a gradient. 
    • The higher internal concentration of glucose, relative to the plasma, pulls in water and makes RBCs swell.
  14. Hyperglycemic macrocytosis
    • the phenomenon that the higher internal concentration of glucose, relative to the plasma, pulls in water and makes RBCs swell
    • can be a source of error in readings reported by automated cell counters
  15. What are red cell indices include
    • MCV (mean corpuscular volume)
    • MCH (mean corpuscular hemoglobin)
    • MCHC (mean corpuscular hemoglobin concentration)
    • RDW (red cell volume distribution width)
    • *can all provide detailed info about size and content of red cells as well as concentration of Hgb.
    • These values are vital in classifying anemias and understanding their causes
  16. MCV
    • first index reported on CBC, measure of RBC size
    • only 3 possible findings:
    • microcytic, macrocytic, and normocytic
    • *is first value cited when grossly describing an anemia
  17. what is a low MCV indicate
    • microcytic anemia
    • results most commonly from:
    • iron deficiency (most common in US and worldwide)
    • beta-thalassemia minor (most common hemolytic disorder)
    • differentiation is vital, as tx is entirely different.
    • may have identical Hgb and Hct values.
  18. what is Mentzer index
    • a simple formula, usually more than 90% accurate, used in making dx btwn iron def and beta-thalassemia minor
    • based on CBC values alone
  19. How to use Metzer index
    • If RBC are microcytic, divide the MCV by the RBC
    • If result is more than 13 = iron deficiency
    • If result is less than 13 = beta-thalassemia minor
  20. What is iron-deficiency anemia attributed to?
    chronic blood loss until proven otherwise
  21. Therefore, What can MCV/RBC values tell you?
    • *recall Mentzer index
    • An index above 13 in a microcytic anemia might prompt a clinician to look for a source of chronic blood loss
    • An index less than 13 might cause one to question any order to transfuse or administer iron, since pt may not be losing blood or need iron
  22. How can nurses assess for b12 deficit
    • decreased vibratory sensation in lower extremities 
    • yellow-blue color blindness
    • both highly suggestive of b12 deficit and precursors to more severe, permanent neuro damage
  23. What happens if B12 deficiency is misdiagnosed & treated as folic acid defic
    • MCV falls to normal, all signs of anemia vanish.
    • On surface, situation may appear resolved BUT irreversible neuro damage can ensue:
    • pt develops psychosis, ataxia, and neuro deficits that mimic MS
    • *For these reasons, providers give BOTH b12 and folic acid supplements to pat with macrocytic anemia when specific cause is unknown.
    • Nurse should question an order that offers only folic acid to correct elevated MCV
  24. Common meanings for abnormal values of: WBC
    • Low: immunosuppression
    • High: infection/inflammation
  25. Common meanings for abnormal values of:
    • Low:  Hemorrhage/IV fluids
    • High:  Dehydration/shock
  26. Common meanings for abnormal values of:
    • Low: hemorrhage/IV fluids
    • High:  Dehydration/DKA/CHF
  27. Common meanings for abnormal values of:
    • Low: Hemorrhage/IV fluids
    • High: DKA/dehydration
  28. Common meanings for abnormal values of:
    • Low: chronic blood loss, iron defic
    • High:  Alcoholism, b12 or folic acid deficit
  29. Common meanings for abnormal values of:
    • Low: iron defict
    • High: Alcoholism
  30. Common meanings for abnormal values of:
    • Low: thalassemia
    • High: N/A
  31. Common meanings for abnormal values of:
    • Low: marrow suppression
    • High: Acute hemolysis
Card Set
CBC basics
CBC basics