Method and apparatus for controlling the washing step in a blood centrifugation cell

A method for controlling a washing step in a blood centrifugation cell wherein washing solution is introduced into the blood centrifugation cell in the washing step, the cell containing compacted red blood cells and supernatant at the beginning of the washing step, the method comprising:

• providing a blood centrifugation cell, a pump for communicating liquid to the blood centrifugation cell, and a computer configured to receive data and produce at least one output;
• providing first input data to the computer indicative of the total volume of liquid that has entered the cell during the filling step that precedes the washing step and during the washing step itself, the liquid being blood during the filling step and the liquid being washing solution during the washing step;
• providing second input data to the computer indicative of the hematocrit value of the blood that was introduced during the filling step;
• providing third input data to the computer indicative of the geometric characteristics of the cell;
• processing the first, second, and third input data in the computer to produce a first output, said first output being the concentration of the supernatant in the supernatant-washing solution mixture that is present in the cell during the washing step, said first output being produced by the computer executing an algorithm that expresses the supernatant extinction law inside the cell using the first, second, and third input data;
• and
• stopping the washing step when a certain concentration of supernatant in the supernatant-washing solution is reached.