A measurement apparatus (30;130) for enumeration of white blood cells in a blood sample, the apparatus comprising: a holder (32; 132), which is arranged to receive a sample acquiring device (10; 110; 410; 510) comprising a measurement cavity (20; 120) that holds a sample, wherein the measurement cavity (20; 120) is adapted to hold a stained and hemolysed blood sample, and wherein the measurement cavity (20; 120) has a uniform depth of 50-200 micrometers, an imaging system (36; 136) adapted to acquire a plurality of magnified digital images of the sample at different levels in a direction of depth of field in the sample by providing a main lens that is movable between well-defined positions along the optical axis, wherein the imaging system (36; 136) is arranged to obtain said digital images with a depth of field in the range of 2-30 micrometers, and an image analyser (46; 146), which is arranged to analyse each acquired digital image for identifying stained white blood cells and determining the number of white blood cells in the sample, wherein the image analyser (46; 146) is arranged to analyse each acquired digital image for identifying white blood cells that are imaged in focus and determining types and number of these white blood cells, the types being distinguished by size and/or shape of the stained white blood cells, whereby the ratio of different types of white blood cells in the sample is determined, wherein the image analyser (46; 146) is arranged to, for a specific white blood cell, determine the number of said images in which said white blood cell is imaged counting from an image in which the white blood cell is determined to be out of focus in a first direction, to an image in which the white blood cell is determined to be out of focus in a second direction, said first and second directions being opposite normals to a focus plane, and wherein the image analyser (46; 146) is arranged to determine, based on the counted number of images, the radius of curvature of said white blood cell. a holder (32; 132), which is arranged to receive a sample acquiring device (10; 110; 410; 510) comprising a measurement cavity (20; 120) that holds a sample, wherein the measurement cavity (20; 120) is adapted to hold a stained and hemolysed blood sample, and wherein the measurement cavity (20; 120) has a uniform depth of 50-200 micrometers, an imaging system (36; 136) adapted to acquire a plurality of magnified digital images of the sample at different levels in a direction of depth of field in the sample by providing a main lens that is movable between well-defined positions along the optical axis, wherein the imaging system (36; 136) is arranged to obtain said digital images with a depth of field in the range of 2-30 micrometers, and an image analyser (46; 146), which is arranged to analyse each acquired digital image for identifying stained white blood cells and determining the number of white blood cells in the sample, wherein the image analyser (46; 146) is arranged to analyse each acquired digital image for identifying white blood cells that are imaged in focus and determining types and number of these white blood cells, the types being distinguished by size and/or shape of the stained white blood cells, whereby the ratio of different types of white blood cells in the sample is determined, wherein the image analyser (46; 146) is arranged to, for a specific white blood cell, determine the number of said images in which said white blood cell is imaged counting from an image in which the white blood cell is determined to be out of focus in a first direction, to an image in which the white blood cell is determined to be out of focus in a second direction, said first and second directions being opposite normals to a focus plane, and wherein the image analyser (46; 146) is arranged to determine, based on the counted number of images, the radius of curvature of said white blood cell.