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TNI Standards Guidance

Disclaimer: This material represents the opinion of its authors. It is intended solely as guidance and does not include any mandatory requirements except where such requirements are referenced. This guidance does not establish expectations of being implemented universally, exclusively, in whole, or in part.

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Module: Quality Systems


Subject: Surrogates

Question 1

In going from the 2003 standard to the TNI standard, a "should" has been changed to "shall" with respect to qualifying sample results when surrogate recoveries fail to meet acceptance criteria. The new standard language is very vague and provides little direction for laboratories. What does "evaluated for the effect indicated for the individual sample results" mean? Does it mean if one surrogate fails, all results must be qualified? Does it mean that a relationship must be established between each analyte and each surrogate? Is such a relationship to be based on chemistry or comparable retention times? The qualification of a selected list of analytes form a long list of sample analytes creates a messy reporting situation. Any clarification of expectations on this will help.

The change of “should” to “shall” indicates that the standard has changed from a recommendation to a requirement.  The NELAC standard requires that the laboratory report any data performance issues to the client that may impact the data quality.  There are no set protocols for handling surrogates, that apply universally, and comments on how individual surrogates apply to individual analytes is beyond the scope of the NELAC standard.  The decision to qualify either the surrogate alone or all compounds affected should be based on compliance with client requirements, compliance with the method requirements, and compliance with quality system procedures established by the laboratory.   Typically, each surrogate is associated with specific/assigned compounds, thus suggesting that all associated compounds related to an individual failed surrogate, should be qualified.  Based on section 1.7.3.3.3.c, surrogates should be chosen based on similar chemistries.  The statement “evaluated for the effect indicated for the individual sample results” means that the qualifier should represent how the sample results may be biased based on the surrogate failure.  In cases were surrogate criteria are not method defined, the laboratory must generate its own internal acceptance criteria.



References:

2009 TNI 1.7.4.3.c

Surrogate Spikes - The results are compared to the acceptance criteria as published in the mandated method.  Where there are no established criteria, the laboratory shall determine internal criteria and document the method used to establish the limits. Surrogates outside the acceptance criteria shall be evaluated for the effect indicated for the individual sample results. The appropriate corrective action may be guided by the data quality objectives or other site-specific requirements. Results reported from analyses with surrogate recoveries outside the acceptance criteria shall include appropriate data qualifiers.

2009 TNI 1.7.3.3.3.c

Surrogates, when required, are chosen to reflect the chemistries of the targeted components of the method and are added prior to sample preparation/extraction.

2003 NELAC D.1.1.3.3.d

Evaluation of Criteria and Corrective Action:  The results are compared to the acceptance criteria as published in the mandated test method.  Where there are no established criteria the laboratory should determine internal criteria and document the method used to establish the limits.  Surrogates outside the acceptance criteria must be evaluated for the effect indicated for the individual sample results.  The appropriate corrective action may be guided by the data objectives or other state specific requirements.  Results reported from the analysis with surrogate recoveries outside the acceptance criteria should include appropriate qualifiers.