A measurement apparatus includes a cooling device including two separated, different substances exhibiting an endothermic reaction when combined to decrease a temperature of the cooling device and a contacting mechanism to contact an assay surface with the cooling device. The apparatus includes a temperature measurement device to measure a temperature of the assay surface and an infrared radiation detector to measure infrared radiation emitted or absorbed. A data processor is configured to determine a concentration of a substance in the subjects body using the measured temperature and the infrared radiation. A measurement method includes using the cooling device and decreasing a temperature of the assay surface to a lower temperature, then measuring a temperature of the assay surface during an increase of the temperature. An infrared radiation detector measures infrared radiation emitted from or absorbed by the assay surface during the temperature increase from the lower temperature.
