Background and objectives: Perfusion index (PI) has recently attracted considerable interest and started to be investigated as a cost-effective diagnostic tool due to its non-invasive character. However, its potential as a painless marker of blood glucose concentration remains to be explored. This study aimed to assess the usefulness of perfusion index (PI) in estimating blood glucose using conventional and ultrasound-assisted finger photoplethysmography (PPG) in the near-infrared (NIR) wavelength range. Method: A customized module combining a reflective PPG sensor with a peak emission wavelength of 940 nm and an ultrasonic sensor with an operating frequency of 40 kHz was developed. 4-min PPG recordings (two minutes with ultrasound; two minutes without ultrasound) were acquired from 36 healthy volunteers after conventional blood sample collection via an invasive glucometer. We computed Pearson's coefficient (r) and the mean absolute error (MAE) to explore the relationship between PI and glucose values and evaluate the performance of the proposed approach, with and without ultrasound.Results: When ultrasonic waves were applied, PI showed a higher correlation with blood glucose levels (r = -0.92, p < 0.001), and MAE significantly decreased (p = 0.036), thereby increasing the precision of the blood glucose estimate.Conclusions: These findings support the idea of combining non-invasive technologies to compensate for the limitations of each other and improve the performance of non-invasive blood glucose monitoring approaches, especially those based on PPG.