Alternate Site Testing Inaccurate During Rapid Changes in Blood Glucose Levels

According to two separate reports in the June issue of Diabetes Care, during rapid changes in blood glucose levels, testing is significantly more accurate when blood is sampled from the fingertip than from the arm or thigh.

In one study, Drs. Theodor Koschinsky and Karsten Jungheim, of the German Diabetes Research Institute in Duesseldorf, tested capillary blood from the forearm and from a fingertip every 15 minutes while subjects were fasting, after an oral glucose load, and after administration of short-acting insulin.

Included in the study were 17 insulin-treated patients. Three different blood glucose monitors approved for analysis of blood from different sites were used. In addition, blood from all patients was analyzed in a clinical chemistry laboratory by a hexokinase-based method.

In the other study, by Dr. John M. Ellison and associates of LifeScan, Inc., in Milpitas, California, the researchers tested blood collected from the forearm, the thigh, and fingertips of 42 patients prior to and after a meal. This group used two different instruments to measure blood glucose--a self-monitoring meter and a biochemistry monitor that employs a glucose oxidase method.

Results were similar in both trials. Finger glucose concentrations peaked by 90 minutes, but measurements from the forearm and thigh didn't peak until approximately 120 minutes, and peak measurements were lower in the latter group. Differences were significantly different among sampling sites at 60 minutes (p < 0.01).

In both trials, variations by site of blood sampling were similar regardless of which system was used to measure glucose levels. Also, both groups demonstrated that rubbing the skin failed to entirely mitigate the differences observed between sites.

Even so, alternative site testing represents a major advance for people with diabetes mellitus, and  the meters are accurate and can be used at different sites during the basal state. Patients should be advised, however, that within 2 hours after a meal, or if they have symptoms of hypoglycemia, they should use fingertip blood. Diabetes Care 2002;25:956-960,961-964.