Red cell count, red cell indices which means cell volume, mean cell hemoglobin, mean cell hemoglobin concentration, hemoglobin, hematocrit, total leukocyte count, differential leukocyte count (three-part or five-part), and platelet count are all measured by most automated hematology analyzers.
Measurement of Hemoglobin
A modified cyanmethemoglobin technique is used to assay hemoglobin directly (all hemoglobins are converted to cyanmethemoglobin by potassium ferricyanide; cyanmethemoglobin has a broad absorbance peak at 540 nm). Some analyzers employ sodium lauryl sulfate which is a nonhazardous reagent. For quick red cell lysis and to reduce turbidity produced by cell membranes and plasma lipids, a nonionic detergent is used.
Measurement of Red Blood Cell Count and Mean Cell Volume (MCV)
Aperture impedance or light scatter analysis are used to directly quantify red cell count and volume. Cell counts are represented on the Y-axis in a red cell histogram, while cell volume is indicated on the X-axis (see Figure 808.1). The analyzer counts the cells as red cells, with a volume ranging from 36 to 360 fl. MCV is used to categorize anemia into three types: microcytic, macrocytic, and normocytic.
Measurement of Red Cell Distribution Width (RDW)
RDW is a quantitative measure of red cell size variation represented as the red cell size distribution’s coefficient of variation. It’s the same thing as anisocytosis on a blood smear. In certain analyzers, it is obtained from the red cell histogram. In iron deficiency anemia, RDW is frequently increased, but not in -thalassemia minor or chronic illness anemia (other causes of microcytic anemia).
This separation, though, isn’t absolute, and there’s a lot of overlap amongst patients’ values. Raised RDW necessitates a blood smear test.
Measurement of WBC Differential
Hematology analyzers can provide a 3-part differential (differential count reported as lymphocytes, monocytes, and granulocytes) or a 5-part differential (differential count reported as lymphocytes, monocytes, and granulocytes) (lymphocytes, monocytes, neutrophils, eosinophils, and basophils). Electrical impedance volume measurement of leukocytes is used in the three-part differential counting method. On the Y-axis of a volume histogram for WBCs, the approximate number of cells is displayed, while the cell size is plotted on the X-axis. Hematology stains are used to stain the blood marks.
Lymphocytes are defined as cells with a volume of 35-90 fl, mononuclear cells are defined as cells with a volume of 90-160 fl, and neutrophils are defined as cells with a volume of 160-450 fl (see Figure 808.2). The analyzer flags any variation from the predicted histogram, requiring a blood smear inspection. To avoid missing aberrant cells, a substantial percentage of 3-part differential counts are ‘tagged.’
Measurement of Platelet Count
Because of their tiny size, wide range of sizes, proclivity for aggregation, and size overlap with microcytic red cells, cellular fragments, and other detritus, platelets are difficult to count. This problem is solved in hematology analyzers by mathematically analyzing platelet volume distribution and converting it to a lognormal distribution.
Platelets are counted in the RBC aperture using the electrical impedance technique, and a histogram is created with platelet volume on the X-axis and relative cell frequency on the Y-axis. A normal platelet histogram has a single right-skewed peak. The analyzer classifies particles larger than 2 fl and less than 20 fl as platelets.
The mean platelet volume (MPV) and platelet distribution width are two further platelet metrics that may be calculated utilizing computer technology from the platelet histogram (PDW). Reticulated platelets are a parameter that some analyzers can generate.
MPV is a mathematical measure that determines the average size of platelets. The average MPV is 7-10 fl. The presence of immature platelets in circulation causes an increase in MPV (> 10 fl); platelet destruction induces megakaryocytes to manufacture such platelets (e.g. in idiopathic thrombocytopenic purpura). The presence of tiny platelets in circulation causes a decrease in MPV ( 7 fl) (in conditions associated with reduced production of platelets in bone marrow).
Measurement of Reticulocyte Count
Various fluorescent dyes can bind to reticulocyte RNA, and the fluorescence can then be measured using a flow cytometer. Because young reticulocytes have more RNA, they glow more brightly.
The hemoglobin content of reticulocytes is a measure that evaluates the newly generated red cells. It’s a marker for iron insufficiency.
Measurement of WBC Cytogram
Each dot in the scattergram represents a cell of a specific volume and density, with the placements of dots in the graph defined by side scatter, forward scatter, light absorption by the cell, and cytochemical labeling (if used). The Y-axis represents the forward angle light scatter (FALS), while the X-axis represents the side scatter (SS).
Low FALS and SS indicate lymphocytes; rising FALS and SS indicate monocytes, neutrophils, and finally eosinophils in the graph. Basophils are counted using a separate technology.
Hematology analyzers can quickly perform a full blood count on whole blood samples (CBC). The red blood cells (RBCs), and white blood cells (WBCs) count, platelets, hemoglobin concentration, hematocrit, RBC indices, and a leukocyte differential are among the results.