Erythrocyte indices

When a patient has a lower than normal hemoglobin, it is important to determine whether red blood cells are of normal size and if they have a normal concentration of hemoglobin. These measurements, known as erythrocyte or red blood cell indices, provide important information about various types of anemias.

Mean corpuscular volume (MCV) measures the mean or average size of individual red blood cells. To obtain the MCV, the hematocrit is divided by the total RBC count. The MCV is an indicator of the size of red blood cells. If the MCV is low, the cells are microcytic or smaller than normal. Microcytic red blood cells are seen in iron deficiency anemia, lead poisoning and the genetic diseases thalassemia major and thalassemia minor. If the MCV is high, the cells are macrocytic, or larger than normal. Macrocytic red blood cells are associated with pernicious anemia and folic acid deficiencies. If the MCV is within the normal range, the cells are referred to as normocytic. A patient who has anemia from an acute hemorrhage would have a normocytic anemia.

Mean corpuscular hemoglobin (MCH) measures the amount, or the mass, of hemoglobin present in one RBC. The weight of hemoglobin in an average cell is obtained by dividing the hemoglobin by the total RBC count. The result is reported by a very small weight called a picogram (pg).

Mean corpuscular hemoglobin concentration (MCHC) measures the proportion of each cell taken up by hemoglobin. The results are reported in percentages, reflecting the proportion of hemoglobin in the RBC. The hemoglobin is divided by the hematocrit and multiplied by 100 to obtain the MCHC.

The MCH and the MCHC are used to assess whether red blood cells are normochromic, hypochromic, or hyperchromic. An MCHC of less than 32% or an MCH under 27 %. indicates that the red blood cells are deficient in hemoglobin concentration. This situation is most often seen with iron deficiency anemia.

Normal values for erythrocyte indices are:

• MCV:
  • MCV values are higher in newborns and infants
  • Men: 80-98 fl (femoliters)
  • Women: 96-108 fl
• MCH - 17-31 pg (picograms)
• MCHC- 32-36%

Anemias can be classified using erythrocyte indices in the following way:

• MCV, MCH and MCHC normal --- normocytic, normochromic anemia --- most often caused by acute blood loss
• Decreased MCV, MCH, and MCHC --- microcytic, hypochromic anemia --- most often caused by iron deficiency
• Increased MCV, variable MCH and MCHC --- macrocytic anemia --- most often caused by Vitamin B12 deficiency (due to pernicious anemia) and folic acid deficiency

Abnormal erthryocyte indices are helpful to classify types of anemia. However, diagnosis must be based on the patient's history, physical examination, and other diagnostic procedures.

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