A blood test method including (a) centrifuging a mammalian blood sample into a plasma and blood cells; (b) removing buffy coats from the blood cells to obtain red blood cells containing solutes confined therewithin; (c) washing the red blood cells with a buffered physiological saline solution and isolating the washed blood cells; (d) mixing the washed red blood cells with a buffered physiological saline solution to obtain a suspended liquid; (e) centrifuging the suspended liquid to remove a supernatant and to obtain a red blood layer; (f) mixing the red blood layer with a hypertonic solution and maintaining the resulting suspension at a temperature of 25 to 40.degree. C. for a period of time sufficient for the solutes confined in the red blood cells to penetrate into the hypertonic solution; (g) centrifuging the suspension to obtain a supernatant containing the solutes; and (h) measuring the supernatant for at least one factor selected from a glucose concentration, a pyruvic acid concentration, a lactic acid concentration and an oxidation-reduction potential.