Abstract: A blood test instrument using a disposable cartridge and a method of measuring a blood sample using the instrument are disclosed. The instrument includes a cell counting station for counting blood cells by electrical resistance measurement, a pressure actuating component adapted to apply a pressure alternately on two flexible receptacles of a disposable cartridge removably placed in the instrument to cause flowing of a mixture of a blood sample and a liquid agent between the two receptacles to obtain proper mixing, and a conduit adapted to deliver the mixture to the cell counting station for counting. After measuring the blood sample, the instrument withdraws a washing liquid contained in another receptacle of the disposable cartridge and uses the washing liquid to clean the instrument and to deliver the mixture back to the cartridge for disposal.