A sample acquiring device for volumetric enumeration of white blood cells in a blood sample, said sample acquiring device comprising: a measurement cavity for receiving a blood sample wherein the blood sample is undiluted whole blood which has been directly acquired into the measurement cavity, said measurement cavity having a predetermined fixed thickness, measured such that said thickness, when the device is in use, in combination with an area of the sample being imaged defines a volume of analysed sample; wherein the sample acquiring device further comprises: a reagent, which is arranged in a dried form on a surface defining the measurement cavity, said reagent comprising a haemolysing agent for lysing red blood cells in the blood sample, and a staining agent for selectively staining white blood cells in the blood sample; a sample inlet, which is defined between opposite walls within the sample acquiring device, said walls being arranged so close to each other that a capillary force may be created in the sample inlet; said measurement cavity being arranged in communication with said sample inlet;and a body member having two planar surfaces to define said measurement cavity, wherein the planar surfaces are arranged at a predetermined distance from one another to determine a sample thickness for an optical measurement, and wherein the planar surfaces of said measurement cavity are arranged closer together than said walls of the sample inlet, such that a capillary force may draw blood from the sample inlet into the measurement cavity. a measurement cavity for receiving a blood sample wherein the blood sample is undiluted whole blood which has been directly acquired into the measurement cavity, said measurement cavity having a predetermined fixed thickness, measured such that said thickness, when the device is in use, in combination with an area of the sample being imaged defines a volume of analysed sample; wherein the sample acquiring device further comprises: a reagent, which is arranged in a dried form on a surface defining the measurement cavity, said reagent comprising a haemolysing agent for lysing red blood cells in the blood sample, and a staining agent for selectively staining white blood cells in the blood sample; a sample inlet, which is defined between opposite walls within the sample acquiring device, said walls being arranged so close to each other that a capillary force may be created in the sample inlet; said measurement cavity being arranged in communication with said sample inlet;and a body member having two planar surfaces to define said measurement cavity, wherein the planar surfaces are arranged at a predetermined distance from one another to determine a sample thickness for an optical measurement, and wherein the planar surfaces of said measurement cavity are arranged closer together than said walls of the sample inlet, such that a capillary force may draw blood from the sample inlet into the measurement cavity. a reagent, which is arranged in a dried form on a surface defining the measurement cavity, said reagent comprising a haemolysing agent for lysing red blood cells in the blood sample, and a staining agent for selectively staining white blood cells in the blood sample; a sample inlet, which is defined between opposite walls within the sample acquiring device, said walls being arranged so close to each other that a capillary force may be created in the sample inlet; said measurement cavity being arranged in communication with said sample inlet;and a body member having two planar surfaces to define said measurement cavity, wherein the planar surfaces are arranged at a predetermined distance from one another to determine a sample thickness for an optical measurement, and wherein the planar surfaces of said measurement cavity are arranged closer together than said walls of the sample inlet, such that a capillary force may draw blood from the sample inlet into the measurement cavity.