How does Squeezing my Finger Affect my Blood Sugar Reading?

Can squeezing a drop of blood from my finger onto the tip of a testing strip really have the potential to affect my blood sugar reading? The simple answer is… maybe.

What does squeezing have to do with blood sugar?

Medical experts have long encouraged diabetics on insulin therapies to not use that first drop of blood – or blood squeezed from the finger – for your first reading.

According to a 2009 study on the topic in the Diabetes Research and Clinical Practice journal[1], the reason for this is that a first drop of blood, or blood that’s been squeezed or ‘milked’ is believed to be diluted with normal interstitial tissue fluid with lower glucose content.

What do the studies say?

The theory continues to cause some debate in medical circles that the presence of interstitial fluid should not alter blood glucose readings. The aforementioned and very small study (10 individuals) did offer a comparison between ‘free flow’ and milked blood drops with a first or second drop without milking. The results?

• Milking/free flow glucose level: 99.0/97.2 mg/dL
• Free flow/second drop blood glucose level: 96.1/96.0 mg/dL

A second study performed in 2011 published in Diabetes Care[2] followed up on the topic and added some additional information regarding accuracy. In this study, 123 diabetic patients were followed. The study resulted in a difference of greater than or equal to (>) 10% in capillary glucose concentrations when measuring the first or second drop of blood.

They also found a difference in the first two drops of blood measured in those who washed their hands before testing and those who didn’t, those who handled fruit before they tested their blood, and those who used external pressure (such as squeezing or milking) around the finger at the time of testing.

The results?

• A difference in glucose concentrations of >10% in the first (11%) and second drops (4%) of blood of those who did not wash their hands.
• In those whose fingers had been exposed to fruit, differences were found in 88% in the first drop and 11% of the second drop in those tested.
• External pressure resulted in >10% difference in 5-13% of those tested.

It can be said that a number of factors besides squeezing or milking the finger can alter that first drop of blood when it comes to testing your glucose levels. Based on the article published in Diabetes Care, diabetic patients are advised to thoroughly wash the hands with soap and water and drying the skin before testing that first drop of blood. 

Note: If your hands are cold or if you have poor circulation, warm your hands ahead of your test rather than squeezing the blood from your finger to increase the accuracy of a reading.

Using the second drop of blood might also remove the possibility of an inaccurate first reading. Always use a new testing strip, clean lancet, and follow instructions from your meter or device regarding prime testing sites, as some meters allow blood from different sites on the body besides the fingers. To be on the safe side, wipe off the first drop of blood from your finger and then place a second drop (not allowing the skin of your finger) to touch the testing strip.

Obtain a good drop of blood prior to placing it on the strip. Not enough of a blood drop can also skew the results. 

FAQ's

1. Does squeezing my finger really affect my blood sugar reading accuracy? Squeezing or milking your finger to obtain a drop of blood for glucose testing can potentially affect the accuracy of your blood sugar reading. Studies have shown that the first drop of blood or blood that has been squeezed may be diluted with interstitial fluid, which has a lower glucose content. This could lead to a slightly lower glucose reading than your actual blood sugar level.

2. What are the findings from studies about using the first drop of blood for glucose testing? Studies have produced varied findings regarding the use of the first drop of blood for glucose testing. One study from 2009 indicated that there could be a difference in glucose levels between milking/free flow blood and a second drop without milking. However, a follow-up study in 2011 found that factors like hand washing, exposure to fruit, and external pressure on the finger could also influence glucose readings.

3. How can I ensure an accurate blood sugar reading while testing at home? To ensure accuracy when testing your blood sugar at home, follow these tips:

   • Thoroughly wash your hands with soap and water before testing to remove any contaminants that could affect the reading.
   • Dry your hands completely to prevent water from diluting the blood drop.
   • Warm your hands if they are cold or if you have poor circulation, as this can help produce a better blood drop for testing.
   • Use a new testing strip and a clean lancet for each test.
   • Follow instructions from your glucose meter or device regarding testing sites and procedures.
   • Wipe off the first drop of blood from your finger and use the second drop for testing, if possible, to reduce the chance of inaccurate readings.

[1]https://www.diabetesresearchclinicalpractice.com/article/S0168-8227(09)00189-2/fulltext

[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3041180/

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