Clinitest test tubes, along with special tablets, were used to detect the presence of glucose in the urine of diabetic patients. By placing urine in the test tube and adding a tablet, the percentage of glucose (g/100ml) could be determined by comparing the colour of the test result with a colour chart provided by the Clinitest manufacturer. If no glucose was detected the contents of the test tube would be blue, otherwise its colour could be green, orange or red, depending on the concentration of glucose.