In April 1961, Mayo Clinic implemented Coulter electronic erythrocyte (red blood cell) counters in the Section of Clinical Pathology. The devices expedited the time required for a blood test, including dilution of the sample, to just a little more than a minute.
As the cells in a diluted blood sample are drawn through an aperture 100 millimicrons in diameter, they lower the electrical conductivity of the electrolyte (sodium chloride) in which they are suspended, causing an impulse to be amplified and record on an electric counter. The device computes the sum of these impulses, applies a “built-in” correction factor, and the number of cells per cubic millimeter of blood is automatically recorded by an electric typewriter on a laboratory report form.
The change-over from the visual to the electronic method of counting red cells was not as simple as purchasing a new device and plugging it into an electrical outlet. Intensive studies of every phase of the new method were carried out over a period of more than year and the successful adaptation of the electronic counter to routine laboratory use came about through the cooperative efforts of many Mayo Clinic personnel.
According to Dr. Don R. Mathieson, head of Clinical Pathology laboratories at the time, “We have in this device an eye which sees and a brain which counts. With it greater accuracy and greater ease in performance have been achieved.”
The classical method for determining the number of red cells in the blood was for a technician literally to count the number of cells visualized through a microscope. An error has high as eight percent was inherent in this method. Using the Coulter counter, the error was reduced to about two percent.
The accuracy of the automatic method is largely the result of the large number of cells counted—the automatic counter counted 50,000 red cells in 15 seconds; the human eye could count only 500 cells in about four minutes.