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, calculated as:

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

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

MCH = (Hgb * 10)/RBC

Mean corpuscular hemoglobin concentration

MCHC = (Hgb * 100) / Hct

Classification:

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

Additional derivations

Mentzer index

Mentzer Index = MCV / RBC Count

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