Glucose Measurement Accuracy

The performance standards for point-of-care testing of blood glucose have changed over time as the devices improved. Initially, the FDA goal was ±15% (1986), but in 1993 the recommendations were updated to ±5% (6). The international standard (ISO DIS 15197) states ±20%, but ±20 mg/dL for glucose levels less than 100 mg/dL (7). A commonly used analysis is the Clarke error grid (8). The Clarke error grid assigns a clinical significance to

Original Error-Grid Analysis

Original Error-Grid Analysis

Blood Glucose Measurement
Reference BG Figure 1 Clarke error-grid analysis.

each measurement error (e.g., data from a device showing an elevation when the reference device reads low would be assigned to region "C" because a patient might be led to "overcorrect" for a false elevation in glucose) (Fig. 1).

When evaluating a continuous glucose monitor, such error grids need to be modified because the direction of glucose movement must also be considered (8). Many factors can affect the accuracy of glucose testing, but newer technology is helping to eliminate these.

One factor leading to testing errors is the requirement for user calibration of the meter. This is usually accomplished by either entering a numerical lot code for test strips or placing a physical "key" into the meter. If the meter is not properly "coded," errors will occur, many having potential clinical significance. Some of the current meters have cleverly eliminated the need for this contrivance so the user is spared from the potential error of improper coding (9). Essentially, all glucose meters have a "control" solution available to verify the meters' accuracy. This solution has a known value and the testing supplies are packaged with the acceptable range of results for the meter. Users should periodically test their device and replace it if the results do not fall within the specified range.

Environmental factors such as temperature, altitude, and humidity may also affect the readings (10), as may hematocrit (11). Physical factors such as inadequate sample size or sugar on the skin surface may also interfere (12). There are a number of medications that may alter glucose levels (e.g., acetaminophen, ascorbic acid, mannitol), which may affect the glucose measurements (13). Recognition of these interfering substances is of critical importance in hospitalized patients with diabetes.

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Responses

  • doreen
    What factors may alter a blood glucose measurment?
    8 years ago

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