Noninvasive Device Computes Blood Glucose Levels

Raman spectroscopy has been used to measure the amount of glucose in the tissue under the skin without the need to perform phlebotomy.

Raman spectroscopy is a technique used to study vibrational, rotational, and other low-frequency modes in a system. It relies on inelastic scattering of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range.

Patients undergoing the oral glucose tolerance test (OGTT) need to have their blood drawn at frequent intervals so that after ingestion of a glucose-rich solution, the level of glucose in the blood can be estimated. This test will determine how quickly glucose is cleared from the blood, an indicator of diabetes, insulin resistance, or reactive hypoglycemia. In a study of 10 healthy volunteers undergoing OGTT, at the Massachusetts Institute of Technology's (MIT) Spectroscopy Laboratory (Cambridge, MA, USA), blood concentrations of glucose were measured every 10 minutes using a clinical glucose analyzer (HemoCue, Inc., Lake Forest, CA, USA).

Raman spectra were collected every five minutes from the forearms of healthy Caucasian and Asian human volunteers undergoing the OGTT. For the excitation source, an 830 nm diode laser was used at an average power of 300 mW on a 1 mm² skin spot. An f/1.8 spectrograph was coupled to a liquid nitrogen-cooled charge-coupled device for spectral dispersion and acquisition, respectively. A dynamic concentration correction (DCC) calibration method was applied to the Raman spectra results for correlation with the blood glucose results.

The Raman technique actually measures the glucose concentration in the interstitial fluid and not the blood. However, this calibration becomes more difficult immediately after the patient drinks the glucose solution because blood glucose soars rapidly, while it takes 5-10 minutes to see a corresponding surge in the interstitial fluid glucose levels. Therefore, interstitial fluid measurements do not give an accurate picture of what is happening in the bloodstream. To compare the two sets of results, the scientists used an algorithm that relates the two concentrations, allowing them to predict blood glucose levels from the glucose concentration in interstitial fluid. After the algorithm was applied, the results from the two sets of data were very similar.

The scientists reported that using DCC-calibrated Raman spectroscopy significantly boost the accuracy of blood glucose measurements with an average improvement of 15%, and up to 30% in some subjects. The study was published in the June 2010 issue of Analytical Chemistry.

Related Links:
Massachusetts Institute of Technology
HemoCue, Inc.