Erythrocyte indices

Also commonly called red blood cell indices or RBC indices, the erythrocyte indices are a set of clinically useful parameters calculated from measurements of erythrocytes. These are commonly reported as part of a complete blood count.

Basic indices

These are computed from the three basic measurements on erythrocytes:

• Hemoglobin (Hgb), in grams per 100ml
• Hematocrit (Hct), a percentage
• Red blood cell count (RBC), millions per cubic micrometer

Mean corpuscular volume

Usually called MCV, this is the average volume enclosed by a red cell, reported as femtograms and calculated as:

 MCV = 10 x (Hematocrit / Red Blood Cell Count)

Some automated blood analyzers measure it directly, rather than calculate it.

It is especially useful in the differential diagnosis of anemia. The basic classification of MCV, using approximate values, is:

• <80: Microcytic
• 80-100: Normocytic
• >100: Macrocytic

Exact cutoffs for each range vary with the patient's age and sex, and both laboratory method and expert opinion. For example, a number of hematologists use < 78 as the beginning of the microcytic range.

Mean corpuscular hemoglobin

Not widely used as a clinical measurement, this is the average weight of hemoglobin per erythrocyte, measured in picograms.

MCH = (Hgb * 10)/RBC

Mean corpuscular hemoglobin concentration

A calculation of the mean amount of hemoglobin per erythrocyte in a specified volume of blood; the amount of hemoglobin relative to the size of the cell, reported in grams per deciliter

MCHC = (Hgb * 100) / Hct

Classification:

• Hypochromic: < 32
• Normochromic: 32-36
• Hyperchromic: > 36

Basic clinical evaluation

These are approximate rules. A given patient with iron deficiency anemia, for example, may present with microcytic but normochromic values.

MCHC	Microcytic MCV	Normocytic MCV	Macrocytic MCV
Hypochromic	iron deficiency anemia lead poisoning thalassemia
Normochromic	renal failure erythropoetin deficiency	Acute blood loss prosthetic heart valves sepsis tumor anemia of chronic disease aplastic anemia
Hyperchromic			chemotherapy folic acic deficiency vitamin B-12 deficiency

Additional derivations

Mentzer index

Mentzer Index = MCV / RBC Count

• Ratio <13: Thalassemia
• Ratio >13: Iron deficiency anemia, Hemoglobinopathies