Dengue Crash Program - Laboratory Diagnosis Hematology

From Complete Blood Counts to Cell Morphology

Hematology Analyzers—From Complete Blood Counts to Cell Morphology

Dengue Crash Program

Laboratory Diagnosis

Hematology Analyzers—From Complete Blood Counts to Cell Morphology

The first group of tests help in making a primary presumptive diagnosis, Treatment and Control of dengue infection. The most important test is complete blood count. With use of complete blood count, the classical dengue triad can be seen, including increased hematocrit (hemoconcentration), atypical lymphocytosis and thrombocytopenia.

Hematology analyzers are used widely in patient and research settings to count and characterize blood cells for disease detection and monitoring. Basic analyzers return a complete blood count (CBC) with a three-part differential white blood cell (WBC) count. Sophisticated analyzers measure cell morphology and can detect small cell populations to diagnose rare blood conditions.

Hematology analyzer technology

The three main physical technologies used in hematology analyzers are: electrical impedance, flow cytometry, and fluorescent flow cytometry. These are used in combination with chemical reagents that lyse or alter blood cells to extend the measurable parameters. For example, electrical impedance can differentiate red blood cells (RBCs), WBCs, and platelets by volume. Adding a nucleating agent that shrinks lymphocytes more than other WBCs makes it possible to differentiate lymphocytes by volume.

Electrical impedance

The traditional method for counting cells is electrical impedance, also known as the Coulter Principle. It is used in almost every hematology analyzer.

Whole blood is passed between two electrodes through an aperture so narrow that only one cell can pass through at a time. The impedance changes as a cell passes through. The change in impedance is proportional to cell volume, resulting in a cell count and measure of volume.

Impedance analysis returns CBCs and three-part WBC differentials (granulocytes, lymphocytes, and monocytes) but cannot distinguish between the similarly sized granular leukocytes: eosinophils, basophils, and neutrophils.

Counting rates of up to 10,000 cells per second can be achieved and a typical impedance analysis can be carried out in less than a minute.

Flow cytometry

Laser flow cytometry is more expensive than impedance analysis, due to the requirement for expensive reagents, but returns detailed information about the morphology of blood cells. It is an excellent method for determining five-part WBC differentials.

A single-cell stream passes through a laser beam. The absorbance is measured, and the scattered light is measured at multiple angles to determine the cell’s granularity, diameter, and inner complexity. These are the same cell morphology characteristics that can be determined manually from a slide.

Fluorescent flow cytometry

Adding fluorescent reagents extends the use of flow cytometry to measure specific cell populations. Fluorescent dyes reveal the nucleus-plasma ratio of each stained cell. It is useful for the analysis of platelets, nucleated RBCs, and reticulocytes.

Proprietary technologies

Manufacturers combine these three technologies with innovative uses of reagents, hydrofluidics, and data analysis tools to produce proprietary methods, each of which has strengths in terms of accuracy, speed, or breadth of parameters.

Ravi Kumudesh, CMLS.SL

Hematology Analyzers—From Complete Blood Counts to Cell Morphology