Principles of Automated Hematology Quiz

History of Hematology Instruments

• First counting chambers (hemacytometers) were devised for viewing and counting cells using a microscope in the late 19th century.
• W.H. Coulter's device counted blood cells using the method of electrical impedance.

Improvements in Hemacytometers

• Researchers improved and standardized hemacytometers by adding a grid pattern, which helped to accurately count cells.
• Later, platelet counting was added to hematology instruments after performing RBC and WBC counts.

Counting Methods

• Early hematology instruments counted blood cells using the electrical impedance method.
• Electrical impedance measures the changes in electrical current when blood cells pass through an aperture.
• In electrical-impedance cell counting, blood cells interrupt the electrical current, which is then measured.

Instrument Accuracy and Precision

• Reliable instrument counts have a coefficient of variation (CV) of <2%.
• Accuracy and precision were improved in electrical-impedance technology by using more advanced electronics and improved aperture designs.

Limitations and Advances

• The first electrical-impedance cell counters had a problem with clogging, which was later improved.
• Until the 1970s, electrical impedance was the only automated cell-counting method.
• Later, light-scatter cell-counting technology was developed, which measures the scatter of light by cells.
• Coulter's principles form the basis for modern cell-counting instruments.

Data Analysis and Display

• A histogram graph typically displays the distribution of cell sizes and counts.
• Electrical impedance measures the changes in electrical current, which are proportional to cell size and volume.