Blood glucose monitoring is necessary for diabetes management, and accurate readings influence daily treatment decisions. A common question arises when supplies expire: what happens when test strips pass their expiration date? Since these strips contain specialized chemistry, their effectiveness is finite, and using them past the recommended date introduces uncertainty.
The Impact of Expiration on Accuracy
Blood glucose test strips contain an immobilized enzyme, most commonly glucose oxidase. This enzyme initiates the chemical reaction necessary for the meter to generate a reading. When a blood sample is applied, the glucose oxidase converts the glucose into other molecules, producing a measurable electrical current or color change. The meter interprets the strength of this signal to provide the final numerical value.
With the passage of time, the enzyme coating on the strip naturally degrades, losing its catalytic activity. This chemical breakdown leads to an incomplete reaction with the glucose in the blood sample. Because the meter receives a weaker signal, the most common result of using an expired strip is an artificially lower reading than the actual blood glucose level. Although the result is unreliable and could theoretically read high or display an error, the loss of enzymatic function biases the inaccuracy toward a falsely depressed number.
Factors Accelerating Strip Degradation
The chemical degradation process leading to expiration can be sped up significantly by improper storage conditions. Test strips are designed to remain stable under specific, controlled environments, and deviations can cause them to fail before the printed date. Exposure to excessive heat is a major culprit, such as leaving the strip vial in a car or near a heat source, which accelerates the breakdown of the glucose oxidase molecules.
Humidity and moisture are equally damaging, as they interfere with the chemical coating and the electrode components. Most strips are packaged in vials containing a desiccant to absorb moisture. Leaving the cap off the vial, even briefly, compromises this protection. Direct sunlight can also damage the strip’s chemistry, leading to premature failure and unreliable results.
Risks of Relying on Faulty Readings
The danger of using a faulty test strip stems from its tendency to read artificially low, creating a false sense of security regarding blood sugar control. A reading significantly lower than the true level can lead to the dangerous decision to withhold or reduce necessary insulin or medication. This under-treatment of actual high blood sugar (hyperglycemia) allows glucose levels to remain elevated.
Sustained, uncorrected hyperglycemia can progress into acute complications such as diabetic ketoacidosis, which requires immediate medical intervention. Conversely, an unreliable strip may occasionally produce a falsely high reading, prompting a patient to administer an unneeded dose of insulin. This misstep can result in severe hypoglycemia (dangerously low blood sugar), causing confusion, seizures, or loss of consciousness.
Ensuring Reliable Results
Maintaining the integrity of test strips is essential for accurate glucose monitoring and safe medication management. Users should check the expiration date printed on the vial or box before use and discard any strips that have passed that date. Once a new vial is opened, note the manufacturer’s recommended “use-by” period, typically three to six months, as strips can degrade even within the expiration window after air exposure.
Proper storage involves keeping the strips in their original, tightly sealed container to prevent exposure to environmental moisture. They should be stored at room temperature, away from direct sunlight, and never kept in places prone to temperature extremes, such as bathrooms or car glove compartments.
To periodically verify the accuracy of the meter and the strips, users can utilize a control solution. This liquid contains a known concentration of glucose, ensuring the resulting number falls within the expected range.