Difference between atypical result_out of trend- out of specification

What is the difference between atypical result, out of expectation and out of trend? As we know in biological products , particularly vaccines, regulatory specification is always set like not less than, as for example not less than 2.5 IU/ dose for rabies vaccine and not less than 20mcg for Hepatitis B and measles & rubella vaccine also have same not less than, in that case how we can set atypical, out of expectation and out of trend considering variability of biological product analysis. Could you Pls explain

Hi Mohammad,

Out of specification (OOS): The test results that fall outside the acceptance criteria established

in SOP. (Against Specification limit).

Out of Trend (OOT): The test results that may be within specification but show significant

variation from the historical results.

OOS (out of specification) 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.

OOS investigations focus on determining the truth about that one value while OOT

investigations focus on understanding non-random changes


The specification limit for assay is: 95.0-105.0 % w/w of label claim

Case-1: For a particular batch, the result obtained 94.2 % w/w -This result is out of the

specification limit. This is called OOS.

Case-2: The result obtained 95.8 % 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 (95.8 % w/w) is called out of


Out-of-Expectation Results (OOE)

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.