Individuals performing self-monitoring of blood glucose (SMBG) at home most commonly use the fingertip as the testing site.1 It has high capillary flow and density that provides a rich blood supply, but is also very sensitive to pain and can pose barriers to consistently performing the test over time. As such, individuals may choose alternate site testing and obtain blood from other parts of the body such as the palm, upper forearm, thigh, calf, or abdomen. Current literature and informal surveys suggest that alternate site testing may appeal to individuals with diabetes by reducing the pain of testing and offering more choices of test sites, potentially improving patient compliance with diabetes management.
Is Alternate Site Testing Accurate?
There are several SMBG devices approved by the Food and Drug Administration for alternate site testing.2 Although alternate site testing can give reliable results, a few factors that may affect their accuracy.
Alternate sites may be more delayed in reflecting rapid changes in blood glucose levels than the fingertip. One study comparing SMBG readings obtained from the fingertip and forearm to laboratory-determined values found that the fingertip blood more closely correlated to the laboratory value. The first asymptomatic hypoglycemic values obtained at the fingertip showed as normoglycemic values at the forearm, taking approximately 30 minutes for the capillary blood glucose levels at the forearm to accurately reflect hypoglycemic values. The reduced capillary flow and density in the forearm is responsible for this delay and should be noted before alternate site testing is utilized. Other studies have also found that testing on the forearm and thigh can yield accurate results only in premeal and steady state levels, whereas the palm may be able to provide accurate results at all times.3–6
Additionally, alternate sites such as the forearm have less capillary volume compared to the fingertip and may not yield adequate amount of blood to perform SMBG.1 However, the amount needed to perform SMBG is usually minimal, and when using a blood glucose meter that requires only small amounts of blood, it should not pose a problem.7
When Should Alternate Site Testing Be Avoided?
Although alternate site testing should be safe and accurate in most circumstances, individuals should NOT utilize alternate site testing in the following circumstances.1 Instead, testing should be done on the fingertip.
- If hypoglycemia is evident
- If the user has hypoglycemia-unawareness
- If the measurement needs to be taken when blood glucose levels are fluctuating
- If there are doubts on whether an adequate amount of blood is being yielded
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