Noninvasive glucose monitoring refers to the measurement of blood glucose levels (required by people with diabetes to prevent both chronic and acute complications from the disease) without drawing blood, puncturing the skin, or causing pain or trauma. The search for a successful technique began about 1975 and has continued to the present without a clinically or commercially viable product. As of 1999, only one such product had been approved for sale by the FDA, based on a technique for electrically pulling glucose through intact skin, and it was withdrawn after a short time owing to poor performance and occasional damage to the skin of users.
Hundreds of millions of dollars have been invested in companies who have sought the solution to this long-standing problem. Approaches that have been tried include near infrared spectroscopy (measuring glucose through the skin using light of slightly longer wavelengths than the visible region), transdermal measurement (attempting to pull glucose through the skin using either chemicals, electricity or ultrasound), measuring the amount that polarized light is rotated by glucose in the front chamber of the eye (containing the "aqueous humor"), and many others.
A 2012 study reviewed ten technologies: bioimpedance spectroscopy, electromagnetic sensing, fluorescence technology, mid-infrared spectroscopy, near infrared spectroscopy, optical coherence tomography, optical polarimetry, raman spectroscopy, reverse iontophoresis, and ultrasound technology, concluding with the observation that none of these had produced a commercially available, clinically reliable device and that therefore, much work remained to be done.
As of 2014, nonregarding the severe shortcomings mentioned above, at least one noninvasive glucose meter was being marketed in a number of countries. Still, as the mean absolute deviation of this device was nearly 30% in clinical trials, 'further research efforts were desired to significantly improve the accuracy [...]'.