Given the drawbacks of the current commonly used diabetes screening methodology—fasting blood glucose—and the fact that more than 20 million people are thought to have undiagnosed diabetes in the U.S. alone, an easier and more convenient screening test would be a very welcome addition to the diabetes testing armamentarium.
Fasting plasma glucose
The limitations of using fasting plasma glucose (FPG) as a screening test for diabetes include the following factors:
- You have to fast overnight before having the test. That means you have to get yourself to a clinic or laboratory in the morning before going to work. Hmmm. Not such an easy thing to do when you have to get the kids to school and yourself to work. So, if you are like me, you keep putting it off and putting it off. It doesn’t mean you are ignoring the need to have the test. It is just a fact that today’s crowded lives don’t mesh well with yesterday’s screening technologies.
- You need to have blood drawn. Again, no big deal for some people, but a dreaded experience for others. I have seen great big guys faint on the spot when they see their blood sucked up into that little tube. So, again, it can be one more reason to put “diabetes screening” on the bottom of the “to-do” list.
- The test misses quite a few cases of diabetes. It only detects elevated glucose when a person is fasting. It does not detect abnormal elevations of glucose after a meal. An even more inconvenient Oral Glucose Tolerance Test (OGTT) is needed for that. This test involves having blood drawn, drinking a standardized glucose-containing solution, and then having blood drawn again 30, 60, and 120, and sometimes 180 minutes later.
So, you may be thinking, what’s the big deal if you put off screening for diabetes. It is because diabetes complications mount up as diabetes remains undiagnosed year after year. That is the reason that many diabetic patients will have one or more irreversible complications at the time they are diagnosed (Harris MI, Diabetes Metab Res Rev 16:230-236, 2001).
SAGE is a new diabetes screening technology. It is short for “Spectroscopic measurement of dermal AGEs.” AGEs are “advanced glycation end products” that form when glucose levels, over time, are elevated. AGEs serve as biomarkers for diabetes. Their levels correlate with existing complications of diabetes and have been shown to predict future complications, such as diabetic kidney or eye disease.
Like A1C (a blood test that measures glycosylation of hemoglobin), but unlike a spot glucose blood test, AGEs are not affected by acute increases in glucose. Therefore, a test that measures skin AGE levels can be performed regardless of whether the individual has fasted or just eaten. This fact, combined with the fact that there is no need to draw blood, makes this technology highly attractive.
AGEs are measured using a spectroscope that measures skin fluorescence. AGE accumulation impacts fluorescence. Since skin naturally accumulates AGEs over a person’s lifetime, it is necessary to apply an algorithm to correct for age.
How does SAGE compare with FPG and A1C testing?
Maynard and his New Mexico colleagues, as reported in Diabetes Care May 2007, performed a head-to-head comparison of SAGE with both FPG and A1C testing. Three hundred and fifty-one (351) people were tested with the SAGE technology in the fasting and fed states. They also underwent FPG, A1C, and OGTT testing. The idea was to see how many of the people who had abnormal OGTT tests (the most sensitive of the diabetes diagnostic tests) also had abnormalities in the other tests. Here is what they found:
- The SAGE test identified almost 29% more individuals who were OGTT “positive” compared to FPG and 17% more than A1C testing.
If these results hold up and if the testing equipment can be made to be both easily transportable and affordable, then this technology could make highly sensitive diabetes screening tests accessible to the millions of individuals who cannot or will not avail themselves of FPG testing. Early diagnosis of opens up opportunities for early intervention and prevention of diabetes complications. This is really exciting.
As always, you must be aware that there is a caveat about this study. The lead author, John D. Maynard, MS works for VeraLight, a for-profit company that is manufacturing the SAGE instruments. Catriona Nguyen, another author on the paper, is affiliated with InLight Solutions, a related company. Although VeraLight’s mission is to
“help stem the tide of the worldwide diabetes epidemic by driving early diabetes detection, thus enabling initiation of therapies that can prevent diabetes or reduce its complications,”
we, nevertheless, need to be cautious about placing too much hope on technology “proven effective” by industry-funded and/or affiliated publications. We have been burned before.