Ektacytometry is a specialized laboratory test that measures the flexibility of red blood cells. It is a diagnostic tool for identifying certain blood disorders by providing quantitative data on how these cells change shape under stress. Analyzing these physical properties offers insights into the health of the cell membrane and helps clinicians understand underlying conditions.
The Importance of Red Blood Cell Flexibility
The primary role of red blood cells is to transport oxygen from the lungs to all body tissues. To accomplish this, they must travel through a network of blood vessels, including microscopic capillaries with diameters smaller than a resting red blood cell. The ability of these cells to deform is necessary for their function.
This flexibility allows them to squeeze through the narrowest passages without rupturing or causing blockages, ensuring smooth blood flow. When red blood cells lose their deformability, they can impede circulation, leading to reduced oxygen supply and potential tissue damage. This impairment is a feature in several hereditary hemolytic anemias.
How Ektacytometry Works
The process begins with a standard blood draw. In the laboratory, red blood cells are isolated and suspended in a viscous solution like polyvinylpyrrolidone (PVP). This suspension is then placed into the ektacytometer, a device that puts the cells in a small gap between two concentric cylinders. One cylinder rotates to create a controlled mechanical force known as shear stress.
This force mimics the stresses red blood cells experience in circulation, causing them to stretch and elongate. A laser beam is directed through the elongating cells, and as the light passes through, it is diffracted, creating a specific pattern. A detector measures this diffraction pattern, as its shape directly corresponds to the degree of cell elongation and provides a precise measurement of deformation.
Understanding the Deformability Curve
Ektacytometry results are presented as a graph called a deformability curve, or ektacytogram. The horizontal axis represents the osmolality of the suspension fluid, which is varied to challenge the cells under different hydration conditions. The vertical axis shows the elongation index (EI), a measure of how much the cells have stretched, with a higher EI value indicating greater flexibility.
A curve for healthy red blood cells has a characteristic S-shape and features points that clinicians use for diagnosis. The maximum elongation index (EImax) represents the peak deformability of the cells. Another point, Omin, indicates the osmotic pressure at which cells are most rigid and begin to lyse, reflecting their osmotic fragility. Deviations in the shape or position of this curve from a normal reference provide information about a red blood cell abnormality.
Diagnosing Conditions with Ektacytometry
Ektacytometry is a primary test for diagnosing hereditary red blood cell membrane disorders. One of the main conditions it identifies is hereditary spherocytosis (HS), a disorder where membrane protein defects cause the red blood cell to become spherical and less flexible. This change results in an ektacytogram where the EImax is decreased and the Omin is shifted to the right, indicating more fragile cells.
The test also identifies hereditary elliptocytosis (HE), where cells are oval-shaped and less deformable. The curve also shows a reduced EImax in this case. Ektacytometry is used for these membrane disorders and provides information for other conditions, such as revealing altered red blood cell properties in certain thalassemias and contributing to understanding sickle cell disease.