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34 HEMOGLOBIN, HEMATOCRIT, MCV (mean corpuscular volume), MCH (mean corpuscular hemoglobin), MCHC (mean corpuscular hemoglobin concentration)




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This article is from the Interpretation Of Lab Test Profiles, by Ed Uthman uthman@neosoft.com with numerous contributions by others.

34 HEMOGLOBIN, HEMATOCRIT, MCV (mean corpuscular volume), MCH (mean corpuscular hemoglobin), MCHC (mean corpuscular hemoglobin concentration)

Strictly speaking, anemia is defined as a decrease in total body red
cell mass. For practical purposes, however, anemia is typically defined
as hemoglobin <12.0 g/dL and direct determination of total body RBC
mass is almost never used to establish this diagnosis. Anemias are then
classed by MCV and MCHC (MCH is usually not helpful) into one of the
following categories:

A. Microcytic/hypochromic anemia (decreased MCV, decreased
MCHC)
Iron deficiency (common)
Thalassemia (common, except in people of Germanic,
Slavonic, Baltic, Native American, Han Chinese,
Japanese descent)
Anemia of chronic disease (uncommonly microcytic)
Sideroblastic anemia (uncommon; acquired forms more often
macrocytic)
Lead poisoning (uncommon)
Hemoglobin E trait or disease (common in Thai, Khmer,
Burmese,Malay, Vietnamese, and Bengali groups)

B. Macrocytic/normochromic anemia (increased MCV, normal MCHC)

Folate deficiency (common)
B12 deficiency (common)
Myelodysplastic syndromes (not uncommon, especially in
older individuals)
Hypothyroidism (rare)

C. Normochromic/normocytic anemia (normal MCV, normal MCHC)

The first step in laboratory workup of this broad class of
anemias is a reticulocyte count. Elevated reticulocytes implies
a normo-regenerative anemia, while a low or "normal" count
implies a hyporegenerative anemia:

1. Normoregenerative normocytic anemias (appropriate
reticulocyte response)

Immunohemolytic anemia
Glucose-6-phosphate dehydrogenase (G6PD) deficiency
(common)
Hemoglobin S or C
Hereditary spherocytosis
Microangiopathic hemolytic anemia
Paroxysmal hemoglobinuria

2. Hyporegenerative normocytic anemias (inadequate
reticulocyte response)

Anemia of chronic disease
Anemia of chronic renal failure
Aplastic anemia*

*Drugs and other substances that have caused aplastic anemia include
the following:

amphotericin    sulfonamides      phenacetin        trimethadione
silver          chlordiazepoxide  tolbutamide       thiouracil
carbamazepine   chloramphenicol   tetracycline      oxyphenbutazone
arsenicals      chlorpromazine    pyrimethamine     carbimazole
acetazolamide   colchicine        penicillin        aspirin
mephenytoin     bismuth           promazine         quinacrine
methimazole     chlorothiazide    dinitrophenol     ristocetin
indomethacin    phenytoin         gold              trifluoperazine
carbutamide     perchlorate       chlorpheniramine  streptomycin
phenylbutazone  primidone         mercury           meprobamate
chlorpropamide  thiocyanate       tripelennamine    benzene

The drugs listed above produce marrow aplasia via an unpredictable,
idiosyncratic host response in a small minority of patients. In
addition, many antineoplastic drugs produce predictable, dose-related
marrow suppression; these are not detailed here.

 

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