Red blood cell indices | MCV, MCH, MCHC, RDW
Red blood cell indices | MCV, MCH, MCHC, RDW
Red blood cell indices are calculated values that allow quantitative characterization of important indicators of the state of red blood cells.
1. MCV — mean cell volume
Calculated by dividing the hematocrit value of 1 mm3 of blood by the number of red blood cells. This is a more accurate parameter than a visual assessment of the size of red blood cells (a 5% change in the diameter of an red blood cell leads to a 15% change in its volume). However, it is not reliable with a large number of red blood cells with an altered shape (MCV may have a normal value if the patient has both pronounced macro- and microcytosis). It should be remembered that microspherocytes have a smaller diameter than normal, while their mean volume often remains normal, so it is always necessary to perform microscopy of a blood smear.
Based on the MCV value, a distinction is made between microcytic anemia (iron deficiency, thalassemia), normocytic (aplastic anemia) and macrocytic (B12- and folate deficiency, aplastic anemia).
Units of measurement: fL (femtoliter, 1 fl = 1 μm3)
Increased MCV (macrocytosis):
Megaloblastic anemia (B12-, folate deficiency);
Macrocytosis (aplastic anemia, hypothyroidism, liver disease, metastases of malignant tumors);
Smoking and alcohol consumption.
Decreased MCV (microcytosis):
Hypochromic and microcytic anemia (anemia due to iron deficiency, chronic pathology, thalassemia);
Hemoglobinopathies;
Hyperthyroidism (rare).
2. MCH — mean cell hemoglobin
Calculated in absolute units by dividing the hemoglobin concentration by the number of red blood cells. This parameter determines the average hemoglobin content in a single red blood cell and is similar to the color index, but more accurately reflects its level in the red blood cell.
Based on this index, anemias can be divided into normo-, hypo- and hyperchromic. Normochromia is typical for healthy people, but can also occur in hemolytic and aplastic anemia, as well as anemia associated with acute blood loss. Hypochromia is caused by a decrease in the volume of red blood cells (microcytosis) or a decrease in the hemoglobin level in a red blood cell of normal volume. That is, hypochromia can be combined with a decrease in the volume of red blood cells, and can also be observed with normo- and macrocytosis. Hyperchromia does not depend on the degree of saturation of red blood cells with hemoglobin, but is determined only by the volume of red blood cells, since an increase in hemoglobin concentration above physiological can result in its crystallization and hemolysis of the red blood cell.
Units of measurement: pg (picogram)
Increased MCH:
Megaloblastic anemia (vitamin B12 and folate deficiency);
Liver disease;
False increase (multiple myeloma, hyperleukocytosis).
Decreased MCH:
Iron deficiency anemia, thalassemia.
3. MCHC — mean cell hemoglobin concentration
Calculated by dividing the blood hemoglobin concentration (in g/100 ml) by the hematocrit and multiplying by 100. The indicator reflects the saturation of the red blood cell with hemoglobin (the concentration of hemoglobin in one red blood cell); characterizes the ratio of the amount of hemoglobin to the cell volume. Thus, it does not depend on the cell volume, unlike the MCH, and is a sensitive test for disorders of hemoglobin formation processes.
Units of measurement: g/L
In fact, an increase in the MCHC cannot be, since an increase in the concentration of hemoglobin above the physiological can result in its crystallization and hemolysis of the red blood cell.
An increase in the MCHC indicates:
Errors at the analytical stage when measuring this sample (errors in determining hemoglobin or the mean volume of red blood cells);
Errors at the preanalytical stage (partial hemolysis of red blood cells).
Decreased MCHC:
Iron deficiency anemia;
Thalassemia;
Some hemoglobinopathies.
With B12 and folate deficiency anemia, MCHC will be normal, and hyperchromia in this case will be due to an increase in the volume of red blood cells.
4. RDW - red cell distribution width
An indicator of red blood cell heterogeneity by volume, characterizes the degree of anisocytosis. According to this parameter, anisocytosis is detected by the device much faster than with a visual inspection of a blood smear. At the same time, the RDW indicator characterizes fluctuations in cell volume within a population and is not associated with the absolute value of the red blood cell volume. Therefore, if there is a population of red blood cells with an altered, but fairly uniform size (for example, microcytes) in the blood, RDW values may be within the normal range.
Units of measurement:
% — percentage deviation of red blood cell volume from the mean value in the population (% spread)
fL — shows the difference between the maximum and minimum red blood cell volume in the population