Diabetic test strips enable millions of people to monitor their blood glucose levels multiple times a day. These strips are coated with specific chemicals that react with glucose in a blood sample. Due to the expense of these supplies, many question whether the printed expiration date is a strict necessity or merely a suggestion. Understanding the science confirms that adherence is a requirement, not a guideline, because the chemical components on the strip degrade over time, directly compromising reading accuracy.
The Science Behind Test Strip Expiration
The function of a blood glucose test strip relies on a biochemical reaction that must occur with high precision. Specialized enzymes, typically glucose oxidase or glucose dehydrogenase, are embedded on the strip’s surface. When blood is applied, the enzyme catalyzes a reaction with glucose, generating a small, measurable electrical current that the meter converts into a numerical reading. Because these enzymes are sensitive biological components, they naturally break down over time, a process known as degradation or denaturing. As the enzyme’s activity decreases, its ability to fully react with the glucose is reduced, leading to an inaccurate measurement.
The printed expiration date guarantees the enzymes remain stable and provide accurate results up to that date, provided the container remains sealed. Opening the vial introduces a new, shorter “use-by” or “discard” date. Once exposed to air, the enzymes degrade much faster due to moisture and humidity. Most brands recommend discarding the strips within three to six months after opening, regardless of the printed expiration date. This dual timeline exists because the chemical coating is extremely vulnerable to environmental changes once the protective seal is broken.
Storage and Handling: Protecting Strip Integrity
While the clock starts ticking on enzyme stability the moment the strip is manufactured, improper storage can significantly accelerate the degradation process. Environmental factors are the primary enemy of strip accuracy, with heat, humidity, and light being the most damaging elements. Exposing the strips to extreme temperatures, such as leaving them in a hot car, can denature the sensitive enzymes long before the expiration date arrives.
Humidity is particularly detrimental because the test strips are designed to absorb moisture from the blood sample to initiate the chemical reaction. If the strips absorb excess moisture from the air, the reaction is compromised before the test even begins, often leading to falsely high readings. For this reason, storing the strips in areas prone to dampness, such as a bathroom or kitchen, is strongly discouraged.
To preserve the strip’s integrity, they must always be kept in their original container. The manufacturer’s vial is designed with a tight-fitting cap and often includes a desiccant to protect the strips from air and moisture exposure. Transferring strips to a pill organizer removes this vital protection and exposes them to contaminants and humidity. After removing a single strip, the vial cap should be closed immediately and tightly to minimize air exposure. Strips should be kept at room temperature in a cool, dry place, away from direct sunlight.
The Clinical Risks of Compromised Readings
The consequence of using an expired or compromised test strip is the unpredictability of the resulting blood glucose reading. Because the chemical reaction is faulty, the meter may display a number that is either significantly higher or lower than the patient’s actual blood sugar level. This inaccuracy forces a patient to make a treatment decision based on incorrect data, which carries considerable health risks.
A falsely high reading might prompt a patient to administer an excessive dose of insulin. This over-correction can lead to severe hypoglycemia, where blood sugar drops too low, potentially causing confusion, seizures, or loss of consciousness. Conversely, a falsely low reading may suggest the blood sugar is safe when it is actually quite high. Under-dosing or withholding necessary insulin due to a faulty low reading can lead to uncontrolled hyperglycemia, which can progress to diabetic ketoacidosis (DKA), a life-threatening medical emergency. Patient safety relies on the confidence that the measurement is accurate, necessitating the use of unexpired and properly stored strips.