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Self-monitoring of blood glucose (SMBG) is an important part of diabetes management. Traditionally, patients have been required to use capillary blood for testing. These blood samples are obtained by sticking the fingertips with lancets. This procedure is often painful for many people, decreasing the likelihood that glucose checks will be performed as recommended for tight diabetes control. New technology now allows blood testing at alternate sites (AST), such as the forearm or thigh. These newer procedures are much less painful for most patients and do not require as much coordination to obtain an adequate blood sample. Some brands of glucometers now require as little as 0.3 ML of blood for testing.
Questions have arisen since the introduction of AST regarding the correlation of results obtained from alternate sites and from the fingertips. Because there is less capillary blood flow and density in the forearm and other alternate sites, samples may not reflect rapidly rising or dropping glucose levels. Failure to detect these rapid changes could result in insulin dosing errors.
Several studies have been published that examine this question. A study by Bina et al examined the impact of prandial state, exercise, and site preparation on the glucose results obtained from the fingertip, palm, thigh, and each forearm.1 The participants consumed a standardized carbohydrate meal and had their glucose measured at 60, 90, and 120 minutes after the meal. The forearm site was prepared with vigorous rubbing at the 90- minute interval. This rubbing is sometimes recommended to improve blood flow to the surface of the skin, theoretically reducing the number of puncture attempts to obtain an adequate blood sample. The participants exercised for 15 minutes after these measurements and again had tests performed at each site.
Significant differences in readings were obtained 60 minutes after the meal and after exercise at the thigh and forearm sites. Measurements (compared with finger stick) were 8.8% lower at the forearm and 13.7% lower at the thigh. In the postexercise period, measurements were 19.1% higher at the forearm and 15.6% higher at the thigh. Readings were similar at the palm and fingertip sites for all intervals. The number of puncture attempts was similar regardless of whether the site was rubbed. The authors concluded that AST was reliable in the fasting state and 2 hours after a meal, but it could not be recommended immediately after a meal or immediately after exercise because of rapidly changing glucose levels.
Another study by Lee et al confirmed these results.2 Patients were asked to measure their glucose at fingertip and forearm sites 10 times a day for 10 days. The data were separated into 4 groups: preprandial, 1-hourpostprandial, 2-hours-postprandial, and bedtime. The largest difference was again noted in the 1-hour-postprandial data. The authors recommended testing only at the fingertips in the immediate postmeal period.
Many patients like AST because of the decreased pain and increased number of sites that can be used for testing. Alternate sites are generally free of food contaminants that may affect results if patients do not wash their hands prior to testing. Fingertip contaminants that are high in sugar may produce falsely elevated glucose readings.3 AST may be a better choice for people whose occupations require significant use of their fingers (eg, musicians), exposure to body fluids (eg, dentists), or exposure to dirt.
Patients may not be aware that AST is an option for them. Many of the newer glucometers allow a choice of AST or traditional fingertip testing. Practice may be required to determine the optimal setting for the lancing device, because it may be more difficult to obtain a sample at alternate sites due to skin thickness.
Education about AST also should include information concerning situations when AST is not advisable. Patients should test at the fingertip when blood glucose levels are changing rapidly, when hypoglycemia is suspected, or if they generally are asymptomatic until blood glucose levels are very low.4,5 If patients are about to engage in activities in which hypoglycemia could be harmful (eg, jogging, driving), it may be advisable to test at both sites. If there is a significant difference, one should assume that the glucose level is dropping and have a snack prior to activity.
AST offers patients more options for glucose testing and generally is preferred to fingertip testing.6 More research is required to determine whether it increases adherence to SMBG recommendations. Pharmacists can play a significant role in the education of patients regarding the appropriate use of AST.
Dr. Garrett is a clinical pharmacist practitioner at Cornerstone Health Care in High Point, NC.
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