A rapid immunochromatographic assay system is provided for measuring the amount of glycated albumin in a blood sample relative to the total level of albumin in the sample. The assay system is comprised of a disposable cassette that contains the test strips and testing reagents, and a measurement device that automatically reads, calculates and displays the test results over a period of time. The test cassette contains two test strips that are used to measure glycated albumin and total albumin respectively. The strips are contiguous beneath the single sample application well so that the same sample is tested simultaneously by both test strips. Part of the sample will migrate thru the glycated albumin test strip where it will react with the glycated albumin test reagents to yield a glycated albumin result, while part of the sample will migrate thru the total albumin test strip where it will react with the total albumin test reagents to yield a total albumin result. The test cassette is placed within a measuring device such as a reflectance spectrometer or fluorometer, that reads, calculates and expresses the result as the percentage of glycated albumin relative to total albumin in the sample. The results of successive testing that are performed over a period of time are stored in the instrument's memory and displayed in a numerical or graphical format so that the individual's glycated albumin levels can be monitored over time.