Method and an apparatus for determining the number of particles or cells

Abstract

A method and apparatus for determining the number of particles or cells in a liquid sample. The method comprises a) determining the number of particles or cells in a first volume of the liquid sample, b) determining the statistical uncertainty of the determined number of particles in said first volume, c) if the determined uncertainty is larger than a pre-determined value, determining the number of particles or cells in a further volume of the liquid sample, d) adding the numbers of cells or particles determined in steps a) and c), e) determining the statistical uncertainty of the number of particles determined in step d), f) repeating steps d) and e) with a further volumes of the liquid sample, until the uncertainty determined in step e) is lower than said pre-determined value or until a pre-determined total volume of the liquid sample in which the number of cells or particles has been determined exceeds a pre-determined volume being larger than said first volume. In this way, the volume examined and the uncertainty of the measurement may be selected so that a suitable compromise between the uncertainty and the time required to perform the measurement can be obtained. The apparatus according to the invention comprises a liquid flow system allowing the measurement sequence to be interrupted as soon as the calculating means decide that the uncertainty of the actual cell count is small enough to rely on the present determination. The apparatus will then be ready to carry on with the next sample, thereby maintaining a high capacity while obtaining reliable cell counts.