Noninvasive In vivo Estimation of HbA1c Based on Beer Lambert Model from Photoplethysmogram Using Only Two Wavelengths

Abstract: Glycated hemoglobin (HbA1c) is the most important factor in diabetes control. Since HbA1c reflects the average blood glucose level over the preceding three months, it is unaffected by the patient's activity level or diet before the test. Noninvasive HbA1c measurement reduces both the pain and complications associated with fingertip piercing to collect blood. Photoplethysmography is helpful for measuring HbA1c without blood samples. Herein, only two wavelengths (615 and 525 nm) were used to estimate HbA1c noninvasively, where two different ratio calibrations were applied and performances were compared to a work that uses three wavelengths. For the fingertip type, the Pearson r values for HbA1c estimates are 0.896 and 0.905 considering ratio calibrations for blood vessel and whole finger models, respectively. Using another value (HbA1c) calibration in addition to ratio calibrations, we can improve this performance, such that the Pearson r values of HbA1c levels are 0.929 and 0.930 for blood vessel and whole finger models, respectively. In the previous study using three wavelengths, the Pearson r values were 0.916 and 0.959 for the blood-vessel and whole-finger models, respectively. Here, the RCF of SpO2 estimation is 0.986 when SpO2 ratio calibration is applied, while in the previous study, the RCF values of SpO2 estimation were 0.983 and 0.986 for the blood-vessel and whole finger models, respectively. Thus, we show that HbA1c estimation using only two wavelengths has comparable performance to previous studies.