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Difference between Out Of Specification (OOS) / Out of Expectation (OOE) / Out of Trend (OOT) - 12 Sep 2014

The terms OOS, OOE and OOT are not new and are always associated with the handling of results/analysis that have deviated somewhat.  But what do the terms actually mean and how may they then be defined?

Some organisations, especially the ECA's Quality Control Working Group (QCWG) has published a Standard Operating Procedure on the handling of OOS results and is expanding this effort to cover OOE and OOT.  However, the QCWG proposes the following definitions for the three terms:

Out-of-Specification (OOS) Results

A result that falls outside established acceptance criteria which have been established in official compendia and/or by company documentation

Out-of-Expectation (OOE) Results

An atypical, aberrant or anomalous result within a series of results obtained over a short period of time is an OOE result. An OOE result is a result that meets specifications, but is outside the expected variability of the analytical procedure

Out of Trend (OOT) Results
A time dependent result which falls outside a prediction interval or fails a statistical process control criterion.

A trend is a sequence of temporal procedures, e.g. for the manufacture of different batches of a product. There are two types of trends:

In one case, no trend is expected, e.g. in production or when analysing process data where everyone expects that they are under statistical control.

In the other case, a trend is expected. One typical example for that is stability testing where one expects that the content of the API reduces over the storage period, or that the quantity of impurities increases over time.

There is a fundamental difference between these two types of OOT results: indeed, in the second situation the dispersion increases over time.

The new Chapter 5 of the EU GMP Guide - coming into force on 1st October 2014 - requires that in future certain data have to be recorded so that trends can be recognized and assessed.


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