Do new methods always have to be validated extensively using worst-case conditions?
It is not always necessary to conduct extensive validations of new methods if they have already been validated in many other TS and there is published literature that demonstrates that the prior validations have been sound and followed validation guidelines. For example, sometimes TS may perform installation and performance qualifications on diagnostic instruments, while omitting an operational qualification.
For example, BSCH guidelines ( #7.2)1 specify that if a laboratory can satisfy itself that sufficient evaluation of a new system has already been carried out in laboratories with a routine environment similar to its own, then validation testing can be done that consists of parallel testing of one week's routine samples. Similarly, Quinley2 allows that an operational qualification may not always be required.
Always consult standards and guidelines applicable to your country and ask regulators questions ahead of time, if possible. When in doubt it is always safest to perform a full validation.
2. Quinley E. Process validation: Will it ever be "no big deal"? Transfusion Diagnostics Update (Ortho-Clinical Diagnostics & Chiron), Sept. 1999:4-5.