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Hematology: Hgb, Hct & RBC Indices

(section 2-2 and 2-3 white text; 253-264 Turgeon)
by

salle sappington

on 3 April 2014

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Transcript of Hematology: Hgb, Hct & RBC Indices

Hematology: Hemoglobin, Hematocrit and RBC Indices
Hemoglobin: heme (iron containing) and globin (protein portion)
Heme: converted to bilirubin then converted to bile salts and pigments (pigments excreted in feces)
The iron is removed, retained, stored & reused in production of new HgB
Globin is protein w/ 4 amino acid chains
Hgb Variants:
normal adult
: Hgb A, 2 alpha globin chains & 2 beta globin chains (95-98%); Hgb A2, 2 alpha & 2 delta gobin chains (2-3%); Hgb F (fetus during gestation) 2 alpha & 2 gamma (2%)
Hgb S:
sickle cell, 2 beta S chains & 2 normal alpha chains; RBCs deform when O2 is decreased
Hgb

C:
rare & mild disease; 2-3% west Africans are heterozygous
Hgb E
: prevalent in SE Asia; 2 copies of beta E chains
hemoglobinopathies (abnormal variants that are clincially significant) - typically have normal # of amino acids, but have a single amino acid substitution
- homozygous: inherit 2 abnormal genes (one from each parent)
- heterozygous: inherit one normal and one abnormal gene; silent carriers - generally don't have health problems
Oxyhemoglobin & deoxyhemoglobin
:
both found in normal blood

Carboxyhemoglobin:
Hgb & CO; Hgb has higher affinity for CO than O and readily combines with CO

Methemoglobin:
Hgb derivative in which iron is oxidized from ferrous state to ferric state, then becomes incapable of combining reversibly with oxygen; typically acquired from certain drugs or chemicals
How do we measure hemoglobin?
specific gravity: only an estimate; drop of blood in copper sulfate; if drop falls rapidly, the SG of blood is greater than copper sulfate

(blood w/ normal Hgb falls rapidly)
Spectrophotometrically:

a. measure cyanmethemoglobin; react blood w/ Drabkins reagent to form cyanmethemoglobin

b. measure azidemethemoglobin; oxyhemoglobin (ferrous iron) is oxidized to form methemoglobin (ferric iron), then combine with azide
Hematocrit
Hct (crit) or packed cell volume (PCV):
macroscopic observation of volume of the packed RBCs in a sample of whole blood (indicates the blood's oxygen carrying capacity)
Measure?
Microhematocrit (manual) or automated (part of a CBC, calculated electronically) (heparinized tubes (red ring) used for capillary samples; unheparinized used for venous blood w/ anitcoagulant)

Used in determining anemias, polycythemia, hemodilution or hemoconcentration
dehydration & polycythemia
anemia or presence of bleeding
Hgb & Hct typically done together and should correlate: for normochromic, normocytic RBCs, the Hct % should be approx 3x the Hgb result
RBC indices - usefel when classifying anemias
Mean corpuscular volume (MCV)
volume or size of avg. RBC
microcytic, normocytic, macrocytic
most reliable automated index for classifying anemias
Hct = MCV x RBC count

Mean corpuscular (cell) hemoglobin (MCH)
represents the weight of Hgb in the avg. RBC
Mean corpuscular (cell) hemoglobin concentration (MCHC)
represents Hgb concentration or color of avg. RBC;
low values indicate hypochromasia (central pallor in RBCs)

Red Cell Distribution width (RDW)
measurement of degree of anisocytosis present, or the degree of variability in RBC size
if anisocytosis present & variation in RBC is prominent, there's an increase in the SD of the MCV from the mean

http://theapstudent.blogspot.com/2012/09/blood-viscosity-and-peripheral.html
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