New Technique Estimates Blood Glucose Through Light Analysis

Diabetes is a prevalent disease for which there is currently no cure. To keep their blood glucose levels (BGLs) under control, people with diabetes must check them regularly and take insulin. BGL measurements almost always require pricking the fingertip to extract blood.

Less invasive options that use contemporary electronics are being actively researched worldwide due to the discomfort of this procedure.

Infrared light measurement is one of the methods proposed thus far to measure BGL; Devices based on mid-infrared light have demonstrated reasonable performance. Nevertheless, integrating the necessary sources, detectors, and optical components into portable devices is expensive and challenging.

On the other hand, cheap components can be used to produce and detect Near-Infrared light (NIR) easily. NIR sensors are widely used in smartphones and smartwatches to measure blood oxygen levels and heart rate. Sadly, glucose lacks distinctive absorption peaks in the NIR range, making it challenging to differentiate it from other blood constituents like lipids and proteins.

To overcome this constraint, a group of researchers headed by Tomoya Nakazawa from Hamamatsu Photonics (Japan) have created a unique approach for estimating BGLs using NIR measurements. Their research has the potential to change noninvasive blood glucose monitoring completely. The study was published in the Journal of Biomedical Optics.

The main output of this work is a novel blood glucose level index, which was created by the research team using fundamental NIR formulas. The first step in their method is to separate the signals of oxyhemoglobin (HbO₂) and deoxyhemoglobin (Hb) from NIR measurements.

By analyzing extensive datasets of NIR measurements, researchers discovered that the phase delay (asynchronicity) between the low-frequency and oscillating components of HbO₂ and Hb signals is intimately linked to the level of oxygen consumption during each cardiac cycle. This phenomenon effectively acts as an indicator of metabolism.

This phase delay-based metabolic index, which has not been reported by other researchers, is a scientifically important discovery.

Tomoya Nakazawa, Study Author, Hamamatsu Photonics

The group then conducted a number of experiments to demonstrate the connection between BGLs and this newly discovered metabolic index. Initially, they covered a healthy subject's finger with the NIR sensor of a commercial smartwatch while it was at rest. After that, the participant drank various sugar-filled and sugar-free beverages to alter blood sugar levels.

A customized smartphone holder with a high-brightness LED was used in similar tests. The metabolic index changes closely correlated with variations in blood glucose levels as determined by a commercial continuous glucose monitor, which made the results extremely promising. This demonstrates a strong correlation between BGLs and the phase delay between HbO₂ and Hb.

Future clinical trials on individuals with diabetes will hopefully confirm the usefulness of the metabolic index in a practical setting. The researchers are optimistic about their novel approach.

The proposed method can in principle be implemented in existing smart devices with a pulse oximetry function and is inexpensive, battery-saving, and simple compared with other noninvasive blood glucose monitoring techniques. Thus, our approach could be a powerful tool towards portable and accessible BGL monitoring devices in the future.

Tomoya Nakazawa, Study Author, Hamamatsu Photonics

Hopefully, this work will lead to useful, non-invasive strategies for people with diabetes to manage their blood glucose levels, reducing the severity of their condition.

Journal Reference:

‌ Nakazawa, T., et al. (2024) Non-invasive blood glucose estimation method based on the phase delay between oxy- and deoxyhemoglobin using visible and near-infrared spectroscopy. Journal of Biomedical Optics. doi.org/10.1117/1.jbo.29.3.037001.