Wick Technique: Reference Method for Implanted Glucose Sensors

: The control of function of experimentally implanted glucose sensors needs an independent reference method. Employing saline-impregnated cotton threads, an implanted wick-technique was adopted in dogs to obtain analytical specimen from the subcutaneous interstitial fluid compartment. By measuring the contents of potassium, calcium, and hemoglobin, the centrifuged wick fluid was validated to contain the interstitial concentrations of solutes after an equilibration time of —15 min. Between 2 and 25 mmol/L, the steady state subcutaneous glucose concentration is nearly identical to circulating glycemia. Slow alterations, as during an oral glucose tolerance test, (OGTT) are well paralleled by the levels in the wick fluid. During alterations, however, a distinct delay is observed. The wick-based glucose levels are mirrored by the output of electrochemical sensors implanted at the same site. This method may be used in checking implanted sensors that can otherwise not be calibrated in situ.