Know the Hematimetric Indices?

Mean Corpuscular Volume(MCV):

– Corresponds to the average volume of a population of erythrocytes, expressed in phentoliters (fL).

– Manual MCV is obtained by dividing the volume of packed erythrocytes (hematocrit) by the number of erythrocytes that occupy that volume.

– Automated MCV is obtained directly by electrical impedance or optical dispersion.

– It is the most important index for automation, as it is the basis for the classification of anemias.

Medium Corpuscular Hemoglobin (MCH):

– It is the average content (internal weight) of hemoglobin in a population of erythrocytes, expressed in picograms (pg).

– It is obtained as an average of the weight or the amount of hemoglobin, by mathematical calculation, by the division of the hemoglobin dosed by the number of erythrocytes counted.

– It can be obtained by derivation of the MCV and MCHC determined directly by laser.

– It is important to know how to differentiate the term “content” from the term “concentration”.

Mean Corpuscular Hemoglobin Concentration (MCHC):

– It is the hematimetric index that evaluates the color of erythrocytes and corresponds to the average of the internal hemoglobin concentrations of a population of erythrocytes.

– Manual MCHC is obtained by the formula Hb x 100 / Hto.

– Automated MCHC can be direct or indirect. The hint is obtained by adapting the Wintrobe formula, where the manual hematocrit is replaced by the automated hematocrit, which is calculated by multiplying the MCV by the number of erythrocytes divided by 10: MCHC = Hb x 100 / (MCV x RBC / 10).

– Direct automated MCHC is determined by laser measurement of the internal hemoglobin concentration of each erythrocyte, they sum and divide it by the number of erythrocytes counted.

– The increase in MCHC can occur when there is loss of the erythrocyte area, without loss of hemoglobin content. Example: spherocytosis, hyperosmolar coma, excess anticoagulant or in the presence of sickle cell, among others.

– The decrease in MCHC reflects erythrocyte unsaturation, that is, erythrocytes with a hemoglobin concentration below normal. It occurs in traditional hyperchromia and excessive polychromasia.

– The presence of hypochromia in erythrocytes begins to arise when MCHC is below 32 g/dL but becomes morphologically evident when the value is less than 28 g/dL.

– MCHC (indirect) values that are excessively high or lowered without justification and without confirmation on the smear, in general they are derived from the poor calibration of the devices.

– Non-anemic individuals have MCHC invariably between 32 and 35 g/dL.

– Erythrograms of non-anemic individuals with MCHC values below 31 g/dL or above 35 g/dL, suggest an error in the determination of hemoglobin, erythrocyte count or MCV.

– To certify which of these parameters is incorrect, hematocrit is performed by centrifugation and the results are compared.

– If the hematocrit is much higher than the automated one, it suggests an error in the erythrocyte count or in the MCV (less common).

– If the manual hematocrit is similar to the automated hematocrit, the error must be in the determination of the automated hemoglobin (excessively high).

Erythrocyte distribution range (EDR):

– Reveals numerically the variation in the volume of erythrocytes. It is calculated as the coefficient of variation (RDW-CV) of the frequency of erythrocyte volumes, where RDW = DS of the volume of RBC x 100 / MCV

– Some meters obtain two types of RDW: 1) The RDW-CV (%) based on the coefficient of variation and the RDW-SD (fL) based on the standard deviation.

– It is an index that is equivalent to the degree of anisocytosis, previously obtained only by erythrocyte morphology.

– Through the RDW, the variation in the volume of the erythrocyte became an accurate, reliable and credible quantitative data greater than subjective microscopic anisocytosis.

– Normal RDW reveals homogeneity in relation to the volume of erythrocytes.

– Decreased values have no clinical significance, while elevated values indicate alterations in erythrocyte maturation.

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