According to the method of evaluating IGT of the present invention, amino acid concentration data on concentration values of amino acids in blood collected from a subject to be evaluated is measured, and an impaired glucose tolerance state in the subject is evaluated based on the measured amino acid concentration data of the subject. A first positioning portion extends from the first board and a second positioning portion extends from the second board. Grooves or other flow-guiding elements may confer swirling or rotation of air in or downstream of the air feed passage andor the air bypass passage. In an embodiment, the microtiter plate system includes optically clear well bottoms that permit sensing and measurement of samples through the optically clear well bottoms.