Introduction

In the food industry, major decisions are made on the basis of analytical results. Whether it be nutritional analysis for a food label declaration, or pesticide or microbiological analysis for quality control purposes, it is absolutely imperative that the results are right and interpreted correctly. Correct interpretation itself is dependent not only on the result (i.e. the answer) being correct, but also on the right question having been asked in the first place (i.e. the appropriate analysis having been undertaken).

Microbiological analyses have particular issues associated with them that make it difficult to know in isolation how accurate they are. Different techniques could provide very different results, which in turn could lead to erroneous conclusions if there isn't a full understanding of what analysis was carried out and why. Put simply, the analysts in the laboratory must know which tests to apply and must be able to perform the analyses competently. How can you tell if your laboratory is performing adequately? The answer is to compare your results for a sample containing a known number of the target microorganism(s) with results obtained by other laboratories - that is, participate in a proficiency scheme.

This fact sheet briefly outlines how proficiency schemes work, and why they are important. For more information on proficiency schemes in general, and the Campden Microbiology Proficiency Scheme in particular, please contact Fiona Cawkell on +44(0)1386 842142 or e-mail microproficiency@campdenbri.co.uk.

Why are proficiency schemes necessary?

When carrying out microbiological analyses, there are many areas where inaccuracies or uncertainties could creep in. These include:

• sample handling and storage errors
• inadequate staff training
• incorrect or inappropriate methods
• equipment and culture media failures
• calculation errors
• reporting errors

These might seem to be rather gross 'all or nothing' issues, but they also cover what would be considered to be 'normal' uncertainty factors and margins of error. When they are all added together, the primary concern is that they don't result in an incorrect representation of what the true answer is. More information on calculation of uncertainty in microbiological measurements is given in Campden BRI Guideline 47 - Microbiological measurement uncertainty - a practical guide and in our factsheet 'Uncertainty of measurement: what it means'. To receive a free copy of the latter, e-mail auto@campdenbri.co.uk with the subject line: send uncertainty

Uncertainty measurement cannot, however, be applied to all of the potential problems listed above. To be confident that the methods that you are using are appropriate, that they are being carried out effectively and in the correct way, and that all equipment is operating adequately, you need to test your results regularly against some kind of known standard. Participating in a proficiency scheme is the most effective way of doing this.