1.2: Red Blood Cell Indices, Colour, and Size

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RBC Indices

Red blood cell indices are useful parameters when investigating suspected anemia. They help provide a general idea of the clinical picture, predict the red blood cell appearance, and aid in the classification of anemia. These indices may be calculated using the red blood cell count, hematocrit, and hemoglobin values generated by automated hematology analyzers, or directly measured in the case of MCV, depending on the model of instrument being used.^1,2

1. Mean Cell Volume (MCV)

MCV (fL, 10x^-¹⁵L) = Hct (L/L) x 1000

RBC Count (x10-12/L)

*Reference range: 80-100 fL

MCV is the measurement of the average red blood cell volume and is used to classify red blood cells based on size ^3,4

<80 fL	Microcytic
80-100 fL	Normocytic
>100 fL	Macrocytic

Note: If the MCV is measured directly, it may be increased if there are many reticulocytes present.³

2. Mean Cell Hemoglobin (MCH)

MCH (pg, 10x^-¹²g) = Hb(g/L)

RBC Count (x10-12/L)

*Reference range: 28-36 pg

MCH is the measurement of the average hemoglobin weight in a red blood cell.³

3. Mean Cell Hemoglobin Concentration (MCHC)

MCHC (g/L) = Hb(g/L)

Hct (L/L)

*Reference range: 310-360 g/L

MCHC is the measurement of the hemoglobin concentration in a population of red blood cells. This is used to denote the colour of the red blood cell population.^3,5

<310 g/L	Hypochromic
310-360 g/L	Normochromic
>360 g/L	Check for spherocytes or errors in Hb/Hct measurement (interferences)

4. Red Blood Cell Distribution Width (RDW)

RDW is the coefficient of variation or standard deviation of the MCV. Similar to the RBC indices, it is determined by automated cell counting instruments and is used to predict the degree of red blood cell size variation, known as anisocytosis.^2-4

An increase in the RDW would indicate a higher presence of anisocytosis on the peripheral blood smear.^2-4

A decrease in the RDW is not associated with any known abnormalities.^2-4

*Reference range: 11.5-14.5%

*Please be aware that the reference ranges provided in this book were obtained from multiple sources and may not accurately reflect the values used in your laboratory. References ranges vary depending on institution, patient population, methodology and instrumentation. Laboratories should establish their own ranges based on these factors for their own use.

Size

As previously described, MCV is used to classify red blood cells based on their size.

1. Normocytic RBCs

An interactive or media element has been excluded from this version of the text. You can view it online here:
https://pressbooks.library.ualberta.ca/mlsci/?p=88

Peripheral blood smears showing normochromic, normocytic red blood cells. From MLS Collection, University of Alberta.

Image 1: 100x oil immersion. https://doi.org/10.7939/R3RJ4995W

Image 2: 60x oil immersion. https://doi.org/10.7939/R35M62P2N

The MCV of normocytic RBCs fall within the normal reference ranges of 80-100 fL and the size should be around 7-8µm.^6,7

Size comparison: Mature red blood cells are about the size of the nucleus of a small lymphocyte. It i also a pproximately three normal red blood cells should fit within a normal neutrophil. ⁶

2. Microcytic RBCs

An interactive or media element has been excluded from this version of the text. You can view it online here:
https://pressbooks.library.ualberta.ca/mlsci/?p=88

Peripheral blood smear images show numerous microcytic red blood cells. A small lymphocyte is present and can be used for a size comparison. From MLS Collection, University of Alberta.

Image 1: 50x oil immersion. https://doi.org/10.7939/R3599ZH07

Image 2: 100x oil immersion. https://doi.org/10.7939/R3WS8J199

A microcytic red blood cell measures less than 7-8µm, and has an MCV that is <80 fL. The hemoglobin concentration (MCHC) can be normal or decreased, and can help differentiate different clinical conditions or severities of anemia.

Microcytes are commonly seen with any abnormalities involving hemoglobin synthesis and thus cells often also appear hypochromic. ^3,6,7

Size comparison: Microcytes are smaller than the size of the nucleus of a normal small lymphocyte. If a normal neutrophil is being used for comparison, more than three microcytes can easily fit in a normal neutrophil.

Associated Disease/Clinical States ^7,8:

TAILS:

Thalassemias

Anemia of chronic inflammation

Iron Deficiency Anemia

Lead poisoning

S ideroblastic Anemia

3. Macrocytic RBCs (Round/Oval)