A false low glucose reading occurs when a blood glucose meter displays a result suggesting the blood sugar level is lower than it is in reality, sometimes indicating hypoglycemia when the true level is normal or high. This inaccuracy poses a serious risk because it may prompt unnecessary carbohydrate ingestion or a reduced insulin dose, potentially leading to dangerously high blood sugar levels. Understanding the potential sources of error is the first step toward preventing them. Inaccurate readings can arise from issues with the testing equipment, errors in testing technique, or certain biological and environmental conditions.
Equipment and Test Strip Malfunctions
The chemical integrity of the test strip is a common source of inaccurate readings, often leading to a false low result. Each strip contains an enzyme layer, typically glucose oxidase or glucose dehydrogenase, which initiates a chemical reaction with the blood sample. Exposure to excessive heat, humidity, or air can degrade this enzyme layer, weakening the reaction and producing a falsely suppressed glucose measurement.
Using expired strips also presents a risk, as the chemicals lose reactivity over time. Physical damage to a strip, or using one incompatible with the meter model, can interrupt the electrical signal needed to calculate the result.
The meter itself can contribute to errors, especially if it requires manual coding to match the specific batch of test strips. An incorrect code entered can skew the final result, occasionally leading to an artificially low reading.
A low battery can interfere with the device’s processing speed or display accuracy. Some meter models are sensitive to rapid temperature changes, which affects the meter’s ability to compensate for the external environment.
Errors in Testing Procedure and Sample Handling
The way a blood sample is collected and applied significantly influences the resulting glucose value. A frequent cause of a false low reading is residual substances on the skin at the puncture site. If alcohol used to clean the finger is not allowed to dry completely, the remaining liquid can dilute the blood sample, leading to an artificially lower glucose concentration. Similarly, food residue, lotion, or excessive moisture can contaminate and dilute the sample.
Another common procedural error is “milking” or aggressively squeezing the finger to obtain a blood drop. This action forces interstitial fluid (the fluid between cells) to mix with the capillary blood sample. Because interstitial fluid has a lower glucose concentration, the resulting mixture dilutes the sample, causing a lower-than-actual reading. Applying an insufficient amount of blood to the test strip, known as under-filling, is also a cause for error.
When the blood sample is too small, the meter may attempt to extrapolate a result from a partial chemical reaction, often resulting in a false low reading. Always touch a generous, round drop of blood to the strip and avoid adding a second drop after the first application. Proper handwashing with soap and warm water is the preferred preparation method, as it improves blood flow and removes contaminants without the dilution risk of wet alcohol.
Physiological and Environmental Factors
Certain physiological conditions can interfere with the electrochemical reaction on the test strip, creating a false low result. Hematocrit, the volume percentage of red blood cells in the blood, is a significant factor. High hematocrit, where the blood is thicker, can impede the spread of blood across the sensor area, causing the meter to underestimate the true glucose concentration.
This effect is pronounced in some meter technologies, where high hematocrit levels are associated with falsely depressed glucose readings. Additionally, high levels of triglycerides (a type of fat in the blood) can occupy a larger volume of the sample, displacing the glucose and leading to a false low result.
Environmental conditions also play a role, as the chemical reaction on the test strip is temperature-sensitive. Extreme temperatures, whether too hot or too cold, directly affect the enzyme’s activity, resulting in an inaccurate measurement. If the meter and strips are extremely cold, the reaction rate slows down, potentially causing a false low reading.
Specific medications or chemicals in the blood can interfere with the meter’s analysis. While many common interferents like Vitamin C cause false highs, certain components in critical care settings can cause false lows. High partial pressure of oxygen in patients receiving oxygen therapy, for instance, can compete with the enzyme’s reaction on glucose oxidase-based strips.