Alternate Site Self-Monitoring of Blood Glucose: Right for Everyone?

Self-monitoring of blood glucose(SMBG) is an important part of diabetesmanagement. Traditionally,patients have been required to use capillaryblood for testing. These blood samplesare obtained by sticking the fingertipswith lancets. This procedure is oftenpainful for many people, decreasing thelikelihood that glucose checks will be performedas recommended for tight diabetescontrol. New technology nowallows blood testing at alternate sites(AST), such as the forearm or thigh. Thesenewer procedures are much less painfulfor most patients and do not require asmuch coordination to obtain an adequateblood sample. Some brands of glucometersnow require as little as 0.3 ML ofblood for testing.

Questions have arisen since theintroduction of AST regarding the correlationof results obtained from alternatesites and from the fingertips.Because there is less capillary bloodflow and density in the forearm andother alternate sites, samples may notreflect rapidly rising or dropping glucoselevels. Failure to detect theserapid changes could result in insulindosing errors.

Several studies have been publishedthat examine this question. A study byBina et al examined the impact ofprandial state, exercise, and site preparationon the glucose results obtainedfrom the fingertip, palm, thigh, andeach forearm.¹ The participants consumeda standardized carbohydratemeal and had their glucose measuredat 60, 90, and 120 minutes after themeal. The forearm site was preparedwith vigorous rubbing at the 90-minute interval. This rubbing is sometimesrecommended to improve bloodflow to the surface of the skin, theoreticallyreducing the number of punctureattempts to obtain an adequateblood sample. The participants exercisedfor 15 minutes after these measurementsand again had tests performedat each site.

Significant differences in readingswere obtained 60 minutes after the mealand after exercise at the thigh and forearmsites. Measurements (comparedwith finger stick) were 8.8% lower at theforearm and 13.7% lower at the thigh.In the postexercise period, measurementswere 19.1% higher at the forearmand 15.6% higher at the thigh. Readingswere similar at the palm and fingertipsites for all intervals. The number ofpuncture attempts was similar regardlessof whether the site was rubbed. Theauthors concluded that AST was reliablein the fasting state and 2 hours after ameal, but it could not be recommendedimmediately after a meal or immediatelyafter exercise because of rapidly changingglucose levels.

Another study by Lee et al confirmedthese results.² Patients wereasked to measure their glucose at fingertipand forearm sites 10 times a dayfor 10 days. The data were separatedinto 4 groups: preprandial, 1-hourpostprandial,2-hours-postprandial,and bedtime. The largest differencewas again noted in the 1-hour-postprandialdata. The authors recommendedtesting only at the fingertipsin the immediate postmeal period.

Many patients like AST because ofthe decreased pain and increasednumber of sites that can be used fortesting. Alternate sites are generallyfree of food contaminants that mayaffect results if patients do not washtheir hands prior to testing. Fingertipcontaminants that are high in sugarmay produce falsely elevated glucosereadings.³ AST may be a better choicefor people whose occupations requiresignificant use of their fingers (eg,musicians), exposure to body fluids(eg, dentists), or exposure to dirt.

Patients may not be aware that ASTis an option for them. Many of thenewer glucometers allow a choice ofAST or traditional fingertip testing.Practice may be required to determinethe optimal setting for the lancingdevice, because it may be more difficultto obtain a sample at alternatesites due to skin thickness.

Education about AST also shouldinclude information concerning situationswhen AST is not advisable.Patients should test at the fingertipwhen blood glucose levels are changingrapidly, when hypoglycemia is suspected,or if they generally are asymptomaticuntil blood glucose levels arevery low.^4,5 If patients are about toengage in activities in which hypoglycemiacould be harmful (eg, jogging,driving), it may be advisable totest at both sites. If there is a significantdifference, one should assumethat the glucose level is dropping andhave a snack prior to activity.

AST offers patients more options forglucose testing and generally is preferredto fingertip testing.⁶ More researchis required to determine whetherit increases adherence to SMBGrecommendations. Pharmacists canplay a significant role in the educationof patients regarding the appropriateuse of AST.

Dr. Garrett is a clinical pharmacist practitionerat Cornerstone Health Care in HighPoint, NC.

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