Measuring glycated albumin (glycoalbumin, GA) in tears could be a future way for those with diabetes to monitor their blood sugar levels noninvasively.
In a 100-patient trial, levels of GA in tears were found to be strongly correlated (r = .722; P < .001) with those in the blood.
“GA levels in blood are widely measured in clinical practice in Japan,” said study investigator Masakazu Aihara, MD, PhD, in an interview.
“It’s a biomarker that reflects the 2-week average blood glucose level like fructosamine,” explained the researcher from the department of diabetes and metabolic diseases in the Graduate School of Medicine at the University of Tokyo.
This could make it a better biomarker for detecting earlier changes in blood glucose than glycated hemoglobin (HbA1c), which reflects changes in blood glucose over the preceding 2-3 months.
Prior studies had shown that glucose levels can be measured in tear samples and that tear glucose levels correlated with blood glucose levels, Aihara and fellow researchers observed in a poster presentation at the virtual annual meeting of the European Association for the Study of Diabetes.
“While looking for noninvasive diabetes-related markers, we found that tears contained albumin. Based on this fact, we thought that GA could be measured in tears,” Aihara explained.
Using tears to test for biomarkers is not a new idea – tears not only protect the eye, they contain a variety of large proteins, and their composition can change with disease. Indeed, researchers have been looking at their usefulness in helping find biomarkers for Parkinson’s disease and diabetic peripheral neuropathy.
During their study, Aihara and associates collected tear and blood samples at the same time. Tear samples were assessed using liquid chromatography (LC) and mass spectrometry (MS). An enzymic method was used to measure GA levels in blood. Several diagnosis assay kits for GA are sold in Japan, Aihara said, and at least one of these has U.S. Food and Drug Administration approval.
Multiple regression analysis revealed that the correlation between GA levels in tears and in blood was maintained even after adjustment for age, gender, nephropathy stage, and obesity (P < .001). The results obtained from the tests were thought unlikely to be affected by any changes in the concentration or dilution of tear samples.
“Since GA levels in blood are clinically used in all types of diabetes, GA levels in tears is also expected to be useful in all types of diabetes,” Aihara said, noting that the effects of receiving treatment on GA levels in tears is something that he would like to look at.
The team would also like to optimize how tear samples are collected and reduce the volume of tears that are required for analysis. At the moment tears are collected via a dropper and about 100 mcL of tear fluid is required for measurement.
“At present, it is difficult to measure for dry eye patients because sufficient tears cannot be collected, but if the required amount of tears decreases