dipped the test strip in a specimen of urine and compared the reacted color to a color block chart one minute later. The compact nature of the test prod ucts provided ease of carrying the tests in a pocket or purse. Dip-andread urine glucose tests were not only accepted and used by diabetic pa tients, they also became standard practice in the physician's office and in the hospital laboratory. The evolution of additional dipand-read tests followed quite prompt ly. Albustix, a colorimetric dip-andread test for protein in urine, provides a sensitive test for recognizing early kidney damage, one of the prominent secondary complications of diabetes. A third dip-and-read test soon provid ed by Ames was Ketostix, a rapid col orimetric test for recognizing ketones in the urine. Ketoacidosis is preceded and accompanied by the excretion of ketone bodies in the urine. The use of a urine self-test for ketones by the dia betic patient provides a warning signal of impending ketoacidosis at a time when preventive treatment steps by the patient and his physician can be carried out effectively. Keto-Diastix, a somewhat later combination dip-andread test provides both a glucose and a ketone measurement in a single re agent strip. During the almost three decades that dip-and-read urine tests have been available, a number of products with minor variations have been produced by several companies in different parts of the world. Blood Sugar and Its Use in Self-Testing For many years, diabetics faithfully followed their physicians' advice and checked their urine for glucose two or three times a day and for ketones whenever glucose was positive, record ing the results so that their physicians could look at the records during scheduled appointments. But they had to wait for scheduled visits to physicians or to hospital clinics to find out their blood sugar levels. In 1963 another battle was won in the con
quest of diabetes by analytical chem istry. This was the development and marketing of Dextrostix, a product for measuring blood sugar that required less than two minutes from start to finish. This novel test is based on the same double sequential enzyme reac tion as the dip-and-read urine tests. But the reagent is coated with a semi permeable membrane, and its range of reaction (sensitivity) is adjusted so that it reacts with about 20-500 mg/ dL, whereas urine glucose tests must function in the range of 0-5000 mg/ dL. The procedure for blood glucose determination is to place a large drop of blood (easily obtained from a finger puncture) on the reagent strip, allow it to remain for exactly one minute, wash off the blood and compare the color of the reaction with a color block chart. During the one-minute waiting time, glucose diffuses through the semipermeable membrane into the re agent and reacts to give a blue color. Large molecules, such as hemoglobin and the cells of the blood, are too large to pass through the semipermeable membrane and remain on the surface to be washed away. This system pre vents the red hemoglobin of the blood from masking the developing color. Many laboratory analysts and physi cians saw the advantages of the new test, which would allow them to obtain a blood sugar while the patient was sitting on the opposite side of the desk. And the patient could see that his blood sugar was normal, showing that for the past few hours he had fol lowed his dietary and therapeutic re gime (or that it was abnormally high and that changes had to be made in his treatment). Some physicians even taught their brittle diabetic patients to use the test and thus gave them better control over day-to-day coping with the disease. However, it was not until 1969 with the introduction of the Ames Reflec tance meter that blood glucose moni toring was really put on its way. This small instrument was designed to measure the reflectance of light from a reacted Dextrostix and translate the signal onto a dial face calibrated to show the results in mg/dL. It was ob vious that reading numbers from a dial face gave a great deal of confi dence to users of Dextrostix reagent strips, who were accustomed to seeing results in incremental color block val ues. The original meter has been im proved through several models and today is available as the Glucometer Reflectance Photometer, a small, bat tery-operated, lightweight instrument that automatically times the one-min ute waiting period and signals that the strip should be washed and placed in the instrument for reading. The in strument is shown in Figure 4. There
674 A · ANALYTICAL CHEMISTRY, VOL. 56, NO. 6, MAY 1984
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