Forearm/Alternate Site Testing
What can you tell me about testing from the forearm?
What is the most appropriate time for forearm testing?
Why are there differences between forearm and fingertip results?
What is the percentage of difference when comparing results from the forearm to a result from a fingerstick test result?
What if a patient observes a difference between forearm and fingertip results greater than 20%?
Which result should be used to determine how much medication to take if there is a difference between an forearm test and a fingerstick test?
Can sample size affect the result?
Can certain medications or health conditions affect results from the forearm which are not noticeable when doing fingerstick testing?
Is fasting required when comparing a blood glucose lab test result to a blood glucose meter result using an forearm sample?
Can I compare results obtained using a sample from the forearm with a result from a sample obtained using forearm or finger with a different meter?
Can circulation problems affect results?
Can hematocrit levels affect results?
What can you tell me about testing from the forearm?
Testing from the forearm provides an opportunity to give tender fingertips a break. There are fewer nerve endings in the forearm, so testing is less painful.* Around three out of four people with diabetes who tested on their forearm reported no pain at all or much less pain than a fingerstick.
Before you begin testing using blood from the forearm, be advised to consult your healthcare professional.
When you test under certain conditions, blood glucose test results obtained using samples taken from the forearm may differ significantly from fingertip samples.
The conditions in which differences in blood glucose results between the forearm and the fingertip are most likely to occur are when blood glucose levels are changing rapidly such as following a meal, an insulin dose, or physical exercise.
You should test using the fingertip within two hours after food intake, insulin dose or physical exercise, or when glucose levels may be changing rapidly.
Testing with blood samples from the forearm is appropriate only for testing prior to, or more than two hours after, food intake, insulin dose or physical exercise.
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What is the most appropriate time for forearm testing?
Forearm testing is most appropriate prior to, or more than two hours after meals, insulin dose or physical exercise.
You should use fingertip testing within two hours after meals, an insulin dose or physical exercise, or whenever glucose levels may be changing rapidly.
When initiating post-prandial (after a meal) forearm testing, consider obtaining finger results in conjunction with forearm results to help assess whether the site to site differences are significant.
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Why are there differences between forearm and fingertip results?
Glucose concentrations in the body vary due to different rates of glucose utilization by different body tissues. The varying rates of glucose utilization may be due to varying amounts of muscle and fat tissue in parts of the body, muscular activity, and variations in blood flow. It is not known which of the sites reflects blood glucose values of greatest physiological significance with regard to managing diabetes. However, if a person does experience differences greater than 20% between forearm and fingertip, the fingertip reading should be relied on as this is generally the location that has been used to establish doses of medication.
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What is the percentage of difference when comparing results from the forearm to a result from a fingerstick test result?
For tests before meals, or 2 hours or more after a meal, the forearm and finger results should be within 20% of each other.
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What if I observe a difference between forearm and fingertip results greater than 20%?
When comparing results using a sample obtained from the forearm and from a fingerstick, you should be in a fasting or pre-meal state (to have had no food in the last 2-3 hours).
If a large difference (>20%) between forearm and fingertip is observed when testing is done at the appropriate times, use fingertip testing for all treatment decisions until the reason for the discrepancies can be identified and resolved. Verify the system is performing properly using control solution. The forearm vs. finger test comparison should be tried again later to see if the same discrepancies occur. One single forearm/finger comparison should not be used to judge the success/failure of forearm testing.
Under certain conditions, blood glucose test results obtained using samples from the forearm may differ significantly from fingertip samples.
The conditions in which these differences are most likely to occur are when blood glucose is changing rapidly such as during the two-hour period following a meal, insulin dose or physical exercise.
When blood glucose is falling, testing with a fingertip sample may identify a hypoglycemic (low blood sugar) level sooner than a test with an forearm sample.
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Which result should be used to determine how much medication to take if there is a difference between an forearm test and a fingerstick test?
If there is a difference between a result using a sample from the forearm and a result from a fingerstick test, use the result from the fingerstick.
- Under certain conditions, blood glucose test results obtained using samples from the forearm may differ significantly from fingertip samples.
- The conditions in which these differences are most likely to occur are when your blood glucose is changing rapidly, such as during the 2 hour period following a meal, insulin dose or physical exercise.
- When your blood glucose is falling, testing with a fingertip sample may identify a hypoglycemic (low blood sugar) level sooner than a test with an forearm sample.
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Can sample size affect the result?
Yes, sample size can affect the result. Always follow the instructions in the Owner's Manual for applying blood to the test strip and make sure that the blood sample has completely filled the confirmation window of the test strip.
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Can certain medications or health conditions affect results from the forearm which are not noticeable when doing fingerstick testing?
Apart from physiological differences in the way different areas of the body respond to meals, insulin or physical activity, we are not aware of any health conditions or medications that would affect forearm results differently than finger results.
Certain conditions such as abnormal hematocrit levels or circulation problems can affect blood glucose results, regardless of the testing site location.
Obtain finger results in conjunction with forearm results to help assess whether the site to site difference is significant.
Under certain conditions, blood glucose testresults obtained using samples from the forearm may differ significantly from fingertip samples.
The conditions in which these differences are most likely to occur are when blood glucose is changing rapidly, such as during the 2 hour period following a meal, insulin dose or physical exercise.
When blood glucose is falling, testing with a fingertip sample may identify a hypoglycemic (low blood sugar) level sooner than a test with an forearm sample.
When initiating after-meal (post-prandial) alternate site testing, obtain finger results in conjunction with forearm results to help assess whether the site to site differences are significant.
Return to the Forearm Testing FAQs
Is fasting required when comparing a blood glucose lab test result to a blood glucose meter result using an forearm sample?
As when comparing capillary fingertip results to a venous laboratory value, the sample collections should be performed at the same time when the person is in a fasting state.
When comparing results from the lab and a result using a sample obtained from the forearm on a blood glucose meter, it is best to have had no food in the last 4 hours.
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Can my patients compare results obtained using a sample from their forearm with a result from a sample obtained using forearm or finger with a different meter?
Assessing meter system accuracy by comparing results from two different meters is not recommended since neither device can be considered a true reference value. It is recommended that comparisons be done directly with a laboratory test and a blood glucose test using a sample from either the finger or the forearm with the meter you use most often.
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Can circulation problems affect results?
Yes, circulation problems can affect results whether the sample is obtained from forearm or from fingerstick. Read the Owners' Manual for information on testing precautions and limitations. As stated in the package insert, test results may be falsely low if you are severely dehydrated or severely hypotensive, in shock, or in hyperosmolar state (with or without ketosis). Critically ill people should not be tested with blood glucose meters.
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Can hematocrit levels affect results?
Hematocrit levels can affect results whether the sample is obtained from forearm or from fingerstick. Hematocrit levels less than 30% may cause falsely high readings and hematocrit levels greater than 55% may cause falsely low readings. If the customer does not know their hematocrit level, they should consult their health care professional. Hematocrit levels may be affected by too much squeezing during site preparation. Please check the Owner's Manual or Abbreviated Procedure Guide for Testing Technique. For more information, please call our Customer Service line at 800 524-7226.
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