Managing diabetes requires accurate information about blood glucose levels. A glucose meter provides the data necessary for making decisions about medication, diet, and activity. Since treatment decisions, such as insulin dosing, depend on the meter’s display, users must have confidence in its reliability. Confirming the meter works correctly involves understanding regulatory standards and performing quality checks. Establishing accuracy is a regular part of effective self-management.
Defining Acceptable Glucose Meter Accuracy
Blood glucose meters must fall within a defined margin of error relative to a laboratory reference. Regulatory bodies set specific standards to ensure that home-use meter results are accurate enough for self-management decisions. This acceptable variance is often referred to as the tolerance limit.
In the United States, the FDA requires that 95% of results fall within 15% of a lab value across the entire glucose range. The international standard, ISO 15197:2013, uses a concentration-dependent metric. For readings 100 mg/dL or higher, 95% of results must be within 15% of the lab value.
For readings below 100 mg/dL, the ISO standard requires 95% of results to be within a fixed 15 mg/dL of the lab reference. This means a reading of 100 mg/dL could range from 85 mg/dL to 115 mg/dL and still be technically correct.
Using Control Solution for Verification
The primary method for verifying the function of your glucose meter and test strips is using a specialized control solution. This liquid contains a known amount of glucose, mimicking a blood sample, and confirms the meter’s electronics and test strip reagents are reacting correctly as a system.
Perform a control test when opening a new vial of strips, if readings seem inaccurate, or if the meter has been damaged or exposed to extreme temperatures. Insert a test strip into the meter as usual. Gently invert the control solution bottle to mix the contents, avoiding vigorous shaking.
Dispense a small drop onto a clean surface, discarding the initial drop. Touch the tip of the test strip to the liquid drop to draw the solution into the strip. The resulting reading must be compared to the acceptable range printed on the test strip vial.
If the displayed number falls within the printed range, the meter and strips are functioning properly. Control solutions are typically only viable for 90 days after the bottle is first opened.
Troubleshooting and Comparing Readings
If a control solution test passes but readings still seem inaccurate, the issue often relates to testing technique or environmental factors. Common user errors include not thoroughly washing hands before testing, as residual sugar can artificially elevate the result. Insufficient blood volume or squeezing the finger too hard can also affect accuracy by diluting the sample with tissue fluid.
Environmental conditions can compromise the sensitive enzymes on the test strip. Exposure to excessive heat, cold, or humidity can degrade the chemicals, leading to erratic results. Certain biological conditions, such as severe dehydration or extreme hematocrit levels, can also interfere with the meter’s electrochemical reading process.
A highly effective way to check accuracy is to compare your meter’s reading with a laboratory blood draw. When you go for a lab test, perform a fingerstick test immediately after the technician draws your venous blood sample. The meter’s result should fall within 15% of the lab’s plasma glucose value to confirm accuracy.
This slight difference is expected because the home meter measures capillary whole blood, while the lab measures venous plasma. If your meter consistently produces results outside the acceptable control range or outside the 15% margin compared to a lab test, contact the manufacturer. Persistent inaccuracies indicate a potential device malfunction or faulty test strips, requiring replacement.