Accurate blood glucose testing is essential for managing diabetes and making informed decisions about diet, medication, and physical activity. When people have difficulty obtaining a sufficient blood sample, they often squeeze the finger aggressively. This common practice, meant to force out more blood, can unknowingly compromise the sample’s integrity and lead to skewed results. Following proper technique is crucial for ensuring a reliable blood glucose reading.
How Squeezing Distorts Blood Glucose Readings
Aggressive squeezing or “milking” the finger to create a larger blood drop significantly affects the final glucose measurement. The physical pressure applied to the tissue forces fluid that is not pure capillary blood to mix with the intended sample. This contamination typically results in a reading that is inaccurately lower than the actual glucose concentration in the bloodstream. The goal of the test is to measure glucose from the blood, not the surrounding tissue fluid.
Capillary Blood Versus Interstitial Fluid
The inaccuracy caused by squeezing stems from the difference between the two fluids collected. A proper fingerstick draws capillary blood, which comes directly from tiny blood vessels and provides a current snapshot of blood glucose. Interstitial fluid (ISF) is the fluid that surrounds the body’s cells and tissues. When the finger is squeezed, the pressure draws in this surrounding ISF, diluting the blood sample. Glucose must travel from the capillaries into the ISF, creating a slight time lag between the glucose concentration in the blood and the ISF. This lag means the glucose concentration in the ISF is often lower, especially when blood glucose levels are rapidly changing. Mixing the capillary blood with this lower-glucose ISF registers a falsely reduced glucose level, which can lead to incorrect treatment decisions.
Techniques for Obtaining a Clean Sample
Securing a clean, sufficient blood sample without aggressive squeezing is the best way to ensure an accurate reading. Preparing the hands properly is the first step, as washing them with warm water and soap significantly improves circulation to the fingertips. Warm water helps to dilate the blood vessels, encouraging a free-flowing blood drop after the puncture.
Lancing Technique
Once the hands are clean and dry, gently warming them up, such as by rubbing them together or briefly hanging the arm down, can further promote blood flow. When using the lancing device, prick the side of the fingertip rather than the fleshy pad. The sides have fewer nerve endings and yield a better sample with less discomfort. Ensure the lancing device is set to an appropriate depth for the individual’s skin thickness to achieve a good puncture. After the puncture, allow the blood drop to form naturally without immediate pressure. If a larger drop is needed, use a very gentle, slow “milking” motion starting from the base of the finger and moving toward the puncture site. The goal is a clean, round drop large enough to completely fill the test strip’s sample area.
Other Factors Affecting Test Accuracy
Beyond squeezing the finger, several other common issues can compromise the accuracy of a blood glucose reading. One significant factor is the presence of contaminants on the skin, such as residual sugar from food or fruit, which can cause a falsely high reading if the hands are not thoroughly washed and dried before testing. Using an alcohol wipe without allowing the alcohol to fully evaporate can also interfere with the chemical reaction on the test strip.
Supply Condition and Storage
The condition and storage of the testing supplies also play a role in accuracy. Test strips have expiration dates and must be stored in their original container away from extreme heat, cold, or humidity. Using expired or improperly stored strips can lead to unreliable results due to degradation of the chemical reagents.
Physiological and Environmental Factors
The user’s physiological state can introduce variability. For example, a person’s hematocrit level (the volume percentage of red blood cells in the blood) can affect some meters. Severely high or low levels, such as in cases of dehydration or anemia, may lead to less accurate results. High altitudes and extreme temperatures are environmental factors that can also interfere with the meter’s performance, requiring testing within the manufacturer’s specified conditions.