Subcutaneous Capillary Filtrate Collector for Measurement of Blood Glucose

The capillary filtrate collector (CFC) is a device that creates an ultrafiltrate at 50–100 μl/h from subcutaneous capillaries, and carries this filtrate out of the body for chemical analysis. From inside out, components include three looped hollow fiber ultrafiltration membranes, a polytetrafluor-oethylene (PTFE) cuff, polyurethane tubing, a “Y” connector leading to a sampling port, a hub, and a needle placed into a 5 ml vacutainer tube. Animal studies have demonstrated that the CFC filtrate glucose level is exactly that of blood at the time the filtrate is created. The authors have performed clinical trials to determine the correlation of blood glucose and CFC glucose levels, and the time delay between contemporary samples. Seven diabetic patients wore the CFC device, tubing, and vacutainer tube for 1 month. In home monitored diabetic patients, fingerstick glucose measurements were performed at the usual daily schedule. The vacutainer was then evacuated, and this average sample analyzed and compared with the average of prior blood glucose levels. An optical device then was applied to measure the linear velocity of CFC fluid through external tubing, and predict the time for fluid to pass from fibers to the sampling port (average, 25 min). Capillary filtrate collector samples drawn at this time had glucose concentrations that generally correlated with blood levels. In diabetic patients on hemodialysis, the vacutainer was evacuated at the start of each treatment, and CFC and blood samples were drawn every 20 min during the treatment. Comparison of glucose-versus-time curves indicated a reasonable correlation between blood and CFC samples, with a delay related to flow rate (which declined 50% during dialysis). The CFC may allow blood glucose concentrations to be measured without need for fingerstick sampling. The cell free and protein free CFC filtrate could be analyzed easily by a variety of continuously operating glucose electrodes.