Difference Between Out of Specification and Out of Trend

1. Out of Specification (OOS) is the comparison of one result versus predetermined specification criteria while OOT (out of trend) is the comparison of many historical data values versus time.

2. The term OOS (out of specification), is defined as those results of in-process or finished product testing, which falling out of specified limits, that are mentioned in compendia, drug master file, or drug application.

2. OOS investigations focus on determining the truth about that one value while OOT investigations focus on understanding non-random changes.

Example:
The specification limit for the assay is 95.00-105.00 % w/w of label claim.

Case-1:

For a particular batch, the result obtained 94.4 % w/w - This result is out of the specification limit. This is called the Out of Specification (OOS).

Case-2:

The result obtained 95.6 % w/w. Although the results are well within the specifications, we should compare the result with the previous batches trend. If we found the average value of the trend as 99.0 % w/w then this batch result (95.6 % w/w) is called Out of Trend (OOT).