Beyond Basic Calibration: How Guardbanding Improves Quality in Life Sciences Manufacturing

What Is Guardbanding?

Guardbanding is a technique used to ensure that measurements remain accurate and reliable, even when there is a level of uncertainty or error in the measurement process. A guardband, which narrows the tolerance range of acceptable values for a measured quantity, is used to prevent false acceptances or false rejections, which can occur when the measured value is near the edge of the tolerance boundary and the uncertainty in the measurement is high. Guardbanding is a critical practice in the life sciences industry to ensure the quality and reliability of pharmaceutical products, medical devices, and other regulated products.

Simplifying the Guardbanding Process

Calibration Guardbanding Width

The width of the guardband is typically related to the uncertainty of the measurement. However, while it may be desirable to set the guardband to the actual uncertainty value, this may not always be possible or practical. This is especially true in life sciences manufacturing, where tolerance ranges are often very narrow and setting the guardband to the uncertainty value would result in an overly restrictive range.

In practice, the width of the guardband is often determined by a balance between the desire to prevent false acceptances or rejections and the need to maintain a reasonable tolerance range. The guardband width also depends on specific applications, industry standards and regulations, and the measurement process being used. For manufacturers of products regulated by the U.S. Food and Drug Administration (FDA), a larger guardband may be needed to account for known sources of error or uncertainty, while in other cases a smaller guardband may be sufficient.

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Guardbanding Methods

There are multiple guardbanding methods devised by various authorities and regulatory bodies over the years. The most common methods used by ISO/IEC 17025 accredited laboratories can be grouped into four distinct categories, listed here in order of complexity:

1. Constant Guardbanding Based on Percentage of Tolerance

This method prevents calibrations that have a passing result close to the tolerance limits and may potentially require recalibration soon. For example, a unit that has accuracy of more than 70% of its tolerance range may require adjustment to improve accuracy despite being in the passing range.

2. Taking Measurement Uncertainty Directly Into Account

With this method, the guardband width is determined by the product of the uncertainty value itself. This method works well for situations where the tolerance range is wide and uncertainties are small. These methods are described in ILAC G8:09/2019 and ISO 14253-1.

3. Guardbands Based on the Test Uncertainty Ratio (TUR)

This method accounts for the TUR and adjusts the guardbands for each specific situation. It's used where the tolerance range is very narrow and the uncertainty in the measurement process is high. These methods are described in NCSLi RP10 and the ANSI Z540.3 rulebook.

4. Statistical Guardbanding Based on Probability

These are the most sophisticated methods, calculating guardband width based on desired probability of false accept (PFA) or confidence level. These include Fluke™ RSS method, UKAS M3003, and ANSI/NCSL Z540.3-2006 Method 6, involving statistical tables and complex calculations.

All methods have their advantages and disadvantages. The right choice depends on your specific application, industry standards, regulations, and measurement processes.

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MasterControl's Approach to Guardbanding Calibration

When selecting calibration management software or a computerized maintenance management system (CMMS) solution for your life sciences operation, it's important to confirm how guardbanding is addressed within the platform. Many software solutions claim to support guardbands by simply allowing manual entry of values, but this approach can be cumbersome and error-prone when calculating and implementing guardbands.

MasterControl has simplified guardbanding to a single dropdown selection, where you choose the guardbanding method to be applied and our metrology engine does the rest. The system automatically calculates uncertainty, determines guardband applicability based on the TUR, and calculates the proper guardband width. If a measured value falls within the guardband, the measurement result can be configured to fail altogether or be reported as an ambiguous pass or fail. The system also handles special cases for units significantly out of tolerance, which may require a different calibration approach.

This guardbanding feature exemplifies MasterControl's design philosophy: rather than simply providing tools, we build intelligence into our software so that redundant tasks are automated and the chance of error is significantly reduced. For life sciences manufacturers operating in highly regulated environments, this approach ensures compliance while streamlining operations.

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