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Alternate Site Testing
Test more often with less pain
Mary knows she should check her blood glucose more often. She could see the effect her diet, exercise and medication have on her blood glucose levels and take action, probably gaining better control of her diabetes. However, Mary says frequent testing just makes her fingers hurt too much. She has heard there is something called alternate site testing that is pain-free. Mary wonders what is involved, since she has always been told to check her blood glucose by doing finger pricks.
Your fingertips are used for blood glucose checks because they have a large supply of small blood vessels (capillaries) close to the skin’s surface. It is easy and convenient to obtain an adequate blood sample here. However, a large number of nerve endings in the fingertips make them sensitive to pain from finger pricks.
New technology offers blood glucose testing strips that require smaller amounts of blood. These new strips allow people with diabetes to use different areas of the body that produce a smaller blood sample. These alternate sites have fewer nerve endings to cause pain.
Using an area of the body other than the fingertips to obtain a blood sample is called alternate site testing. The most frequently recommended alternate site is the forearm. However, meters give different manufacturer recommendations. Alternate site testing can also refer to obtaining your blood sample from the upper arm, thigh, calf or your hands. The parts of the hand that can be used are the base of thumb, fleshy parts of the palm, or the fleshy part between thumb and first finger on the top of the hand.
Blood glucose readings obtained from fingertip tests are considered close to the results obtained from a test at the lab. Blood taken from the fingertips is a capillary sample and is sensitive to changing blood glucose levels. Alternate site test readings differ. Blood obtained from alternate sites moves through the tissue beneath the skin and is from deeper blood vessels.
Blood glucose values from alternate sites do not change as rapidly as the blood flowing through the capillaries close to the skin surface in the fingertips. Studies have shown that when blood glucose is steady, as when fasting (no food for eight hours) or before meals, readings compare between fingertip and forearm.
However, when your blood glucose is low or changing rapidly, readings from the forearm may be 20 to 30 minutes behind the reading you obtain from the fingertip. It is believed the same lag time applies to other alternate sites, although these have not been sufficiently tested to confirm this. Always do a fingertip test when you suspect you may be experiencing low blood glucose (hypoglycemia). As well, use the fingertip when your blood glucose may be rapidly changing, such as within two hours after eating, exercising or giving yourself an insulin dose.
Most meters that offer alternate site testing give you two different end caps for your lancet (poker) device so you can do either the fingertip or an alternate site. It is important to use the correct end cap for each site. Check with the manual that comes with your meter or ask your health care provider.
Consider the following when deciding to try alternate site testing
- Use fingertips when you suspect low blood glucose or when your blood glucose is changing rapidly.
- It may be more challenging to obtain a blood sample from an alternate site. (There are fewer blood vessels close to the surface of the forearm.)
- Bruising may occur more easily.
- Areas with large amounts of hair may have less blood flow near the surface. Excess hair may smear your blood sample, making it more difficult to use an alternate site.
- Alternate sites may be more difficult to access and more obvious than using the fingertips.
- The result may vary from site to site, so stay with the same alternate site for consistency.
- Alternate site testing can be a relief to people who use their fingers a lot, such as for typing or playing a musical instrument.
- Do not use alternate site testing if you have a history of hypoglycemia unawareness (no symptoms when your blood glucose is low).
Tips for best results with alternate site testing
- The area should be clean. Use soap and warm water. Avoid using alcohol since it dries the skin out and may cause more pain.
- Rub the area briskly for five to ten seconds to stimulate blood flow.
- Use the correct end piece for your lancet. The correct end piece is clear so you can see the blood drop form before lifting the lancet from the skin.
- Press the lancet firmly against the skin for one to two seconds to encourage the blood to pool. After pricking the skin, leave the lancet device pressed against the skin until a blood drop forms. If necessary, ease the pressure then press back down again to help form the drop.
- Bring your glucose test strip to the blood drop at the correct angle. (See the manufacturer’s instructions.)
- Record results in your logbook, noting which site was used if it was not your fingertip.
Alternate site testing may allow you to test more often with less pain. For example, you can use alternate site testing when you want to check your blood glucose before meals, or two hours after eating or exercising. Save the more painful fingertip tests for when you think you may be experiencing low blood glucose or before driving. As well, use the fingertip test if you want to check your blood glucose when it might be changing rapidly, such as within the first two hours of eating or exercising.
Remember Mary, whose fingers hurt too much from frequent testing? After she incorporated alternate site testing into her blood glucose testing routine, she was able to resume playing the guitar.
table 1. Meters available in Canada offering alternate site testing
* Note - the Sof-Tact device combines lancing and blood application in one system. It uses a vacuum suction action to obtain the larger blood sample required for its strips.
METER |
MANUFACTURER |
APPROVED ALTERNATE SITES |
BG REQUIRED |
TEST TIME |
END CAP |
| Freestyle Blood Glucose Monitoring System | Therasense | Forearm, bicep area, thigh, back of calf, fleshy part of palm between the thumb and first finger | 0.3 ul | 15 seconds | Use clear end cap |
| One Touch Ultra and Induo | Lifescan | Forearm | 1.0 ul | 5 seconds | Use clear end cap |
| One Touch Fast Take | Lifescan | Forearm | 1.5 ul | 15 seconds | Use clear end cap |
| * Sof-Tact | Medisense | Forearm, upper arm, palm of hand | 2.5 ul | 20 seconds | Use appropriate port |
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