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MCV
mean corpuscular volume
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MCH
mean corpuscular hemoglobin
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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
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What noninfectious factors can raise WBC
- examples:
- AE of meds
- trauma
- air pollution
- mental stress
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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
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RBC component
- more than one type is included
- RBC typing is a factor of age, NOT lineage or function
- Some belong to reticulocytes
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When total RBC, both young & old, is below 4.5 million for men and 4 million for women, criterion for anemia is met
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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)
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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)
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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%
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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
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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
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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
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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.
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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
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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
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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
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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.
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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
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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
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What is iron-deficiency anemia attributed to?
chronic blood loss until proven otherwise
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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
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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
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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
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Common meanings for abnormal values of: WBC
- Low: immunosuppression
- High: infection/inflammation
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Common meanings for abnormal values of:
RBC
- Low: Hemorrhage/IV fluids
- High: Dehydration/shock
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Common meanings for abnormal values of:
Hgb
- Low: hemorrhage/IV fluids
- High: Dehydration/DKA/CHF
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Common meanings for abnormal values of:
Hct
- Low: Hemorrhage/IV fluids
- High: DKA/dehydration
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Common meanings for abnormal values of:
MCV
- Low: chronic blood loss, iron defic
- High: Alcoholism, b12 or folic acid deficit
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Common meanings for abnormal values of:
MCH
- Low: iron defict
- High: Alcoholism
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Common meanings for abnormal values of:
- Low: thalassemia
- High: N/A
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Common meanings for abnormal values of:
RDW
- Low: marrow suppression
- High: Acute hemolysis
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