Understanding M40-A2: are your swabs compliant with the standard?

A common and incorrect assumption is that errors in the diagnostic laboratory are most likely to happen during the analytical phase, and therefore laboratories invest time, effort and resources to maintain quality control (QC) programmes and introduce new technologies. However, the majority of errors in laboratory diagnostics occur during the pre-analytical steps of the initial testing process, accounting for up to 70% of all mistakes made in the laboratory. Most of these problems arise from inappropriate sample collection, transportation, preparation for analysis and storage.1 Nowadays laboratories focus on technological improvements and invest money in automation, although this does not take into consideration the fact that the problems arise before the sample arrives at the laboratory.

Plebani and Carraro performed a large, comprehensive study which determined that, of all errors detected, 68.2% originated in the pre-analytical phase, compared with 18.5% in the post-analytical phase and 13.3 % during the analytical phase.2 Therefore, quality indicators should cover all the steps in the pre-analytical phase, from requesting the correct test to specimen storage, with the greatest attention being paid to sample transportation.3 The need for improvement initiatives in this area becomes even more important with the increasing trend towards consolidation of laboratory facilities and concomitant longer distances for specimen transportation. Errors at any stage of the collection and transportation of the sample potentially can lead to serious misdiagnosis for the patient. It is therefore of significant value that the correct transport device is used, ensuring viability of pathogens is maintained during transportation.

Swab transport devices are commonly used in sampling and the material which forms the swab bud as well as the transport medium used have significant implications regarding the recovery of pathogens. These key features are often overlooked. The ideal swab transport device must absorb organisms from the sampling site, maintain viability during transportation, without promoting growth. A swab device must also release bacteria onto the appropriate medium during culture processing in the laboratory. These are the most important aspects to be considered when choosing the appropriate collection device, and these swab characteristics can be tested using the methods provided by the Clinical and Laboratory Standards Institute (CLSI) M40-A2 standard. This is the only recognised international standard evaluating the performance of swab transport systems (STS) in terms of bacteria recovery during transportation. Prior to publication of the M40-A standard by the National Committee for Clinical Laboratory Standards (NCCLS) in 2004, there was no recognised standard for the performance of swab transport systems. In 2014, an updated second edition of the standard was published (M40-A2). In the absence of a standard procedure for determining the effectiveness of STSs, previous studies were less objective as they were not based on any standardised method, bacterial strains and very rarely included any quantitative data. The new standard resolves this in defining whether or not a product is acceptable in terms of bacterial viability and recovery.