Alternative Site Testing – What It Is & When To Use It

By Matthew J. Jaime, RD

The following blog post on Alternative Sight Testing (AST) is from guest contributor Matthew J. Jaime, RD.

Matthew is a dietitian and a type-1 diabetic. As a sophomore in high school, he realized his mission in life was to obtain the education necessary to help others improve their relationship with food & nutrition. 

In 2019, he graduated summa cum laude with a Bachelor of Science in Food & Nutritional Science – Dietetics & Food Administration with a minor in Gerontology (the study of aging). He completed his dietetic internship at UC San Diego Health, graduating in April 2020, and soon after passed his Registration Examination for Dietitians earning his RD credentials.

Currently, he is working as a private practice dietitian and serving as a Trustee on the Board of Directors for the Imperial Valley Wellness Foundation.

What is Alternative Site Testing?

The most common site for a diabetic to test their blood sugar is the fingertip, but any diabetic who tests often every day knows how quickly our fingers can get sensitive and sore. 

That’s where AST can help. 

Most (but not all) modern glucometers are able to assess glucose levels from sites outside of the fingertips including the calf,  the thigh, the forearm,  the palm, and even the abdomen. 

For me, as soon as I discovered how painless my forearm was as a testing site, I never looked back! (even if though I have to apply a lot of pressure for blood to come out)

When should I not use my forearm and go back to my fingertips? 

A few days ago, I posted on my Instagram story about the need to revert back to fingertips as a testing site when blood sugar drops–but the same applies to rapidly rising sugar as well! 

Why?

Scientists have discovered glucose travels much more rapidly to the many capillaries found on the fingertips when compared to other sites around the body. So when blood sugar increases OR decreases very quickly, the most current and accurate reading of blood sugar is going to come from the fingertips.

This is because there is much more interstitial space found in the alternative testing sites versus the capillary-filled fingertips. When you test from an alternative testing site there is a higher degree of plasma from the interstitial space drawn during the test. This is because when sugar is absorbed, it is taken to the interstitial space to be absorbed into the cells, but the sugar found in the interstitial space does not reflect the current level of sugar in the blood–there exists a lag between the two. 

So when is it not recommended to use AST?

  • During or after exercise 
  • If you are sick
  • Just before setting out on a road trip
  • If you think you are going low 
  • If you feel like your blood sugar suddenly spiked (like right after a snack full of quick sugar (candy, juice, soda, etc.))

AST is a great alternative for anyone who feels like their blood glucose testing is getting in the way of their daily lives. Anyone who plays an instrument, used their hands a lot of their job, doesn’t want their hands to get callused from frequent testing, or is just tired of sore fingers can benefit from AST. 

It’s important to have an accurate idea of your blood sugar. If you’ve ever skipped a blood test because you couldn’t stand to prick your finger one more time – AST may be for you.

Citations:

Koschinsky T, Jungheim K, Heinemann L. Glucose sensors and the alternate site testing-like phenomenon: relationship between rapid blood glucose changes and glucose sensor signals. Diabetes Technol Ther. 2003;5(5):829-842. doi:10.1089/152091503322527030

Cengiz E, Tamborlane WV. A tale of two compartments: interstitial versus blood glucose monitoring. Diabetes Technol Ther. 2009;11 Suppl 1(Suppl 1):S11-S16. doi:10.1089/dia.2009.0002