May 10, 2013
BG Testing – Use First or Second Drop?
Have you heard about this before? I admit I had not and I wondered what the significance could be. There is more significance than thought and I will try to cover the reasons and considerations. This originally appeared in February 2012, but has been getting some attention on several diabetes forums again. Some are concerned and others are trying to play it down as old news. I have found that old news can be just as valuable for people recently diagnosed with diabetes because they may not be aware of the old news. On June 15, 2012, the diabetes blog on the Mayo Clinic diabetes page had this blog.
This is a Dutch study and the full text is free at this link. You will need a PDF reader. When they are talking about diabetes educators, they are referring to diabetes educators in Europe. Even these educators give different advice although the majority of the Dutch educators advised patients to wash their hands before testing. To address the different recommendations, they used the following to measure the capillary glucose concentrations. They also compared readings of greater than or equal reading of 10%.
#1. without washing hands
#2. after handling fruit
#3. after washing the fruit-exposed fingers
#4. during the application of different amounts of external pressure around the finger (squeezing).
For measuring equipment, the researchers used the Accu-Chek Compact plus meter with plasma-calibrated test strips (Roche, Almere, the Netherlands). The meter was calibrated prior to the start of the study as well as halfway through the study. No significant changes were observed.
A Speidel and Keller hand blood pressure meter was used to achieve different external pressures. The regular cuff was replaced by a neonatal cuff. One of two available sizes was used depending on the thickness of the finger (Philips, M1866A neonatal disposable cuff #1 and M1868A neonatal disposable cuff #2). This equipment was used to apply standard pressure for the finger pressure we often refer to as milking the finger.
Time interval during measurements were done so that capillary glucose measurements were performed directly following the finger puncture with a maximum delay of 90 seconds between measurements. When using the cuffs, the selected pressure was applied first and then the finger puncture was performed. The two pressures were 40 mmHg and 240 mmHg.
The interesting part of this study is the differences among the educators in their recommendations and then what the patients do in practice. Even more surprising was the number of patients that did not use the side of their fingers for testing.
The conclusions were about what I expected and only one source mentioned what I think many forget in talking about using the second drop of blood. When using the second drop of blood, the lancet must be set deeper, therefore potentially creating more pain in testing to be able to wipe the first drop away and to be able to have a second drop form. The authors do recommend washing hands with soap and water, drying them, and using the first drop of blood.
The authors do recommend using the second drop when washing is not possible and the fingers are not visibly soiled or have not been expose to sugar-containing foods or products. They tell us to wipe away the first drop of blood and use the second. They wisely and with proof from their study advise us not to use external pressure as this creates unreliable results. This applies to testing when the fingers have been exposed to fruit sugars and need to be washed for accurate results.
When using pressure or milking the finger, we need to be concerned about interstitial fluids affecting the results. This is what makes them unreliable. Also by using the second drop, the depth of the lancet can create unwanted pain, but is necessary to obtain the second drop of blood.