Diagnosing Anemia With the CBC

The red cell indicies and peripheral smear can be helpful in making the diagnosis of Anemia, and in orienting the clinician towards the probable cause of the disorder.

Anemia, as we know, arises from several different mechanisms:

1. Blood loss
2. Increased cell destruction (hemolytic anemia)
3. Impaired red cell formation
4. Increased plasma volume

In attempting to classify the type of anemia, the Mean Corpuscular Volume -MCV  (normal value 76-96 fl) -is of great help.

Anemia with a Low MCV (small cells, microcytosis) suggests the possibility ofiron deficiency , especially if there is also a low quantity of hemoglobin (hypochromasia) within each small cell.

Anemia with a normal MCV, and with normal red cells on the smear suggests an anemia of impaired production  - renal failure, chronic illness, marrow supression by drugs.

Also, in acute blood loss, after the blood volume has been allowed to normalize, normocytic cells will be seen.

A frequent misunderstanding is that in acute blood loss, a hematocrit reading will be of value. But, of course, when you lose whole blood quickly you can actually exsanguinate and still have a normal hematocrit. In these situations clinical parameters are of greater use in the first few hours following a major bleed.

Anemia with an increased MCV (macrocytosis) suggests the possibility of vitamn B12 or Folic acid deficiency  (megaloblastic erythropoiesis).

The Peripheral Smear also adds valuable information. As mentioned above, hypochromatic cells, i.e. those that stain lightly, suggest iron deficiency since iron is essential to hemoglobin production.

Macrocytes are often hyperchromatic because they are large, and so contain abundant hemoglobin. This is because B12 and folate are necessary for nuclear maturation, and when deficient, cells are permitted to grow large while accumulating abundant hemoglobin.

In hemolytic conditions, the marrow spits out young cells that still contain cytoplasmic ribonucleic acid and therefore appear blue. These cells are called polychromatic. These young polychromatic cells are also seen a few days after acute blood loss and when iron, B12 and folic acid are administered therapeutically. This, of course, indicates the marrow's replenishing response.

Some less common forms of anemia can be diagnosed or indicated by the peripheral smear.

• Poikilocytes (cells varying in shape, especially tear drop shaped cells) are seen in metastatic disease of the marrow.
• Ovalocytes are seen in the normal red cell population. However, if increased above 30% of the total RBC's they may indicate an inborn trait and lead to hemolysis.
• Stomatocytes , cells that have mouth-like areas of central pallor are sometimes seen in, and may be a clue to alcoholism.
• Reticulocytes: The reticulocyte count is a measure of red cell production. The normal range is 0.5 to 1.5% of the red cell population studied.

In anemias due to increased red cell destruction, i.e. the haemolytic anemias, the reticulocyte count will be elevated unless there is an associated red cell production problem. In anemias due to an impaired production, i.e. aplastic anemias, the reticulocyte count will be reduced or normal.

In general, assessment of reticulocyte numbers tends to be a somewhat insensitive, but useful guide as to the type of anemia. Various correction factors have been applied to the assessment of reticulocyte quantities. However, these tend to be somewhat cumbersome and may lead to unwarranted reliance upon their accuracy.

So, after observing a low hemoblobin, it is useful to glance at the MCV and the peripheral smear. These may provide the clue as to the next step needed to confirm the diagnosis. The above is a superficial discussion of the findings in anemia, but the "berries" are represented.

- Leon Desormeau