Ask the Experts - Noninvasive Glucose Monitoring
How far has noninvasive glucose monitoring progressed?

Pansak Kangsawiwat, MD

It is important to obtain continuous glucose measurement prospectively so that patients can adjust the insulin doses effectively. Continuous glucose monitoring methods are either currently under investigation or have already been approved for use. Numerous companies are currently involved in developing and testing noninvasive and reagentless glucose detection systems.

Two devices that are currently approved in the United States to continuously monitor blood glucose levels are:

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  The GlucoWatch Biographer (Cygnus Inc; Redwood City, California). This is a watch-like device designed to be worn on the wrist, and measures glucose levels in fluid drawn through the skin by low-level electric currents. Electrodes in the Biographer measure glucose as frequently as every 20 minutes for up to 12 hours at a time. The GlucoWatch is not considered a replacement for finger-stick glucose measurements, but is an additional tool to detect trends and patterns in glucose levels. The device was approved by the US Food and Drug Administration in March 2001. It is not yet available for purchase by the US general public.
  
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  Continuous Glucose Monitoring System (CGMS) (Medtronic Minimed; Northridge, California). This system measures glucose in interstitial fluid by a small sensor inserted just beneath the patient's skin. Glucose measurements are sent to the sensor's data collection and control module. Typical measurement periods are 2-3 days. Data gathered over the measurement period are later downloaded into a computer for analysis. The CGMS does not provide real-time glucose values during the measurement period. This method is also not designed to replace finger-stick testing, but may identify patterns or trends in blood glucose levels. The CGMS was approved by the US Food and Drug Administration in June 1999. It is not available to the general public and is only intended for professional use in a clinical setting.
  

The problems with the current technologies are:

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  Both the GlucoWatch and the CGMS require calibration to blood glucose levels.
  
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  Skin irritation and long warm-up time with GlucoWatch and also false or numerous alarm alerts and missed measurements. The GlucoWatch is relatively large in size and may not provide measurements when there is perspiration on the skin. It is calibrated to blood glucose levels after a warm-up period of approximately 3 hours.
  
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  The CGMS provides retrospective data and requires recalibration to blood glucose levels 3-4 times a day.
  
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  Learning how to manage the enormous amount of glucose data with these technologies is another important aspect that requires attention.
  

Research is ongoing on implantable sensors and on methods based on optical technologies such as near-infrared (NIR) absorption spectroscopy, laser polarimetry, and Raman spectroscopy.

GlucoWatch Biographer
Cygnus Inc. Web site: www.glucowatch.com. Accessed December 4, 2001.

US Food and Drug Administration News. FDA Approves New Glucose Test For Adult Diabetics. March 22, 2001 http://www.fda.gov/bbs/topics/NEWS/2001/ NEW00758.html. Accessed December 4, 2001.

Continuous Glucose Monitoring System
Medtronic Minimed Web site: http://www.minimed.com/doctors/md_products_cgms_ ov_completepic.shtml. Accessed December 4, 2001.

US Department of Health and Human Services. FDA Approves New Glucose Test For Adult Diabetics. June 16, 1999.
http://www.fda.gov/bbs/topics/NEWS/ NEW00682.html. Accessed December 4, 2001.