Absolute values of blood indices
Absolute blood indices are essential in diagnosing and typing anemias. A subject’s fundamental values are compared with arbitrarily set typical values. Blood indices have been discarded in favor of absolute corpuscular values.
Table of contents
Mean corpuscular volume (MCV):
Mean corpuscular volume is the volume of a single red blood cell. It is expressed in cubic microns (µm3).
MCV= = PCV per 100 ml of blood divided by RBC count in millions / µL Multiplied by 10.
45/5×10 =90 µm3 (average value)
Range is 78 t0 94 µm3.
If MCV is above the normal range, the RBCs are known as macrocytes, and the condition is macrocytosis.
If MCV is less than the normal range, the RBCs are known as microcytes, and the condition is microcytosis.
If MCV is within the normal range, the RBCs are known as normocytes, and this condition is normocytic.
Mean corpuscular hemoglobin (MCH)
This is the average weight of (amount) of hemoglobin present in an RBC. It is expressed in picograms (10 -12 gm), which are micro-micrograms. We can calculate MCH if we know hemoglobin in grams per deciliter and RBC count in millions /microliter.
MCH= Hb in grams percent multiplied by ten and divided by the number of RBC in million per mm3 of blood.
If the values are
Hb =15 grams%
RBC count= 5 million/mm3.
MCH= 15/5 x10=30 average value.
Typical range is 28-32 picograms(pg).
Mean corpuscular hemoglobin concentration (MCHC)
This is the hemoglobin concentration in a single red blood cell. It indicates the amount of hemoglobin expressed as a percentage of the red blood cell’s volume.
MCHC= = Haemoglobin in grams per decilitre/PCV per 100 ml of blood multiplied by 100.
MCHC= 15/45 X 100= 33.3 % Average value.
The range is 32 to 38 %. ( 35 ± 3%).
In another way, MCHC can be calculated by the following formula
MCHC= MCH divided by MCV and multiplied by 100.
The MCHC value can not exceed 38% because RBCs cannot hold Haemoglobin beyond this metabolic limit—the Haemoglobin-Forming mechanism.
Therefore, RBC is never hyperchromic.
More than 99% of PCV is due to RBC.
MCHC is the most reliable. RBC count is not taken into consideration. Due to its large size, MCH may be high, up to 39 pg in a large red blood cell, but MCHC would be within the normal range.
Colour Index (CI)
The color index is the ratio of Haemoglobin to RBC
Colour Index=haemoglobin % /RBC %
The normal range is 0.85 to 1.15 (1± 0.15).
The average is 1.
14.8 gm /dL hemoglobin is 100%, and 5 million/ µm3 RBC count is 100%.
The color index is low in iron deficiency anemia and high in macrocytic anemia.
RBC count and hemoglobin content may decrease simultaneously. Therefore, CI is not affected.
The color index has no clinical value.
MCD:
Red cell distribution width (MCD) can be measured by direct micrometric measurements of the red blood cells in a stained blood film.
MCAT:
MCD can measure central corpuscular average thickness (MCAT).
Red cell distribution width (RDW):
Red cell distribution width measures the variation in the size of red blood cells. It is calculated as a coefficient of variation (CV) or standard deviation (SD) and is usually part of a complete blood count.
A normal RDW is usually between 12 % to 15%.
A high RDW means there are abundant microcytes and macrocytes. This is seen in dimorphic anemia.
Other conditions associated with increased RDW are inflammation, malnutrition, and renal diseases.
RBC size variation is known as Anisocytosis. (iso=same,cyto= cells.A=no.)
Variation in the shape of RBCs is known as Poikilocytosis.
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