Laboratory Diagnostic Tests

ERYTHROCYTES INDICES

- ERYTHROCYTES INDICES
- THE SIZE AND THE DISTRIBUTION OF ERYTHROCYTES
- ERYTHROCYTES INDICSES – CLASSIFICATION OF ANEMIA

ERYTHROCYTES INDICES

Erythrocytes indices or corpuscular values can be calculated from primary measurements.

MEAN CORPUSCULAR VOLUME OF ERYTHROCYTE AND HEMOGLOBIN CONTENT OF ERYTHROCYTE

MCV (mean corpuscular volume of the erythrocyte)

MCV is measured in cubic micrometers or femtoliters (1fl = 10-15 L).

Reference values:
Adults:                                        MCV = 83-92 fl
Girls and boys 8 - 18 years:         MCV = 77-92 fl

MCH (mean corpuscular hemoglobin in the erythrocyte)
The amount of hemoglobin per erythrocyte can be evaluated from MCH, which is calculated by dividing the amount of hemoglobin per liter of blood by the number of erythrocytes per liter of blood, as follows:

MCH is expressed in picograms of hemoglobin per cell (pg/L, 1 pg = 10-12 g).
Reference values:
Adults:                                        MCH = 27 - 34 pg
Girls and boys 8 - 18 years:         MCH = 24 - 32 pg

MCHC (mean corpuscular hemoglobin concentration)
The concentration of hemoglobin in erythrocytes is determined by dividing the amount of hemoglobin per liter of blood by hematocrit 1/1.

MCHC is expressed in grams of hemoglobin per liter (g/L).
MCV, MCH, and MCHC are average quantities and therefore may not detect abnormalities in the blood with mixed cell populations.

Reference values:
Adults:                                        MCHC = 320 - 345 g/L
Girls and boys 8 - 18 years:         MCHC = 304 - 346 g/L

THE SIZE AND THE DISTRIBUTION OF ERYTHROCYTES is determined by three parameters:

• MCV (mean corpuscular volume of erythrocyte)
• RDW (red cell distribution width)
• Red cell distribution by volume (histogram)

RDW (red cell distribution width)

RDW reflects the size distribution of the erythrocyte population. Most instruments (Coulter, Technicon, and Sysmex) calculate it as a coefficient of variation (CV), i.e., standard deviation of the distribution of RBC volumes divided by the MCV.

RDW is a measurement of anisocytosis.
Reference values:
Adults:                                        RDW = 14.6 - 16.5
Girls and boys 8 - 18 years:         RDW = 11.6 - 14.3

Red cell distribution by volume (histogram)
The histogram of the erythrocyte volume presents the dispersion of the volume of erythrocytes around the mean value.
The histogram of erythrocyte distribution by the volume eliminates the possibility of false normal results that are possible if the size of erythrocytes is calculated only by MCV. When multiple populations of erythrocytes different by volume are present, it is not enough to know MCV values only.
The histogram of erythrocyte volume points at one or more existing populations of erythrocytes. It is a very important predictable indicator of a successful treatment.

                      

    RBC relative
            number

Picture 3. Distribution of erythrocytes by volume in healthy people

The factors that influence the accuracy of the results of erythrocytes distribution by volume are:

• irregular flow of cells through the measuring chamber,
• erythrocyte pairs, agglutinated or aggregated erythrocytes, and
• presence of great number of reticulocytes and leukocytes.

The majority of counters have a built-in program for correcting these interference factors.

ERYTHROCYTES  INDICSES – CLASSIFICATION OF ANEMIA

According to some studies, anemias can be classified according to RDW and MCV:

*Indicates that the red cell distribution histogram is characteristically altered from the usual unimodal distribution.