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All Quality Control questions

Question 8 of 20 Fundamentals Concept

Why does a passing system suitability test not replace method validation?

Short answer

Validation shows once, with designed experiments, that the procedure is fit for its purpose. System suitability checks on each run that the instrument and analysis are performing as they did when validated. A passing SST says today's system works, not that the method measures the right thing accurately.

Why

ICH Q14 defines system suitability tests as checks that verify the measurement system and analytical operations are fit for purpose and that increase the chance of detecting unacceptable performance. Q2(R2) calls them an integral part of the procedure, set during development as a regular check. For a chromatography method, typical criteria are resolution between critical peaks, repeatability of replicate standard injections, tailing factor and signal to noise.

Validation answers different questions. Is the method specific for the analyte in the presence of impurities and degradants? Is it accurate across the range?

How much does it vary between days and analysts? An SST cannot answer these because it usually uses only standards, not samples with real matrix, and it runs under one set of conditions. A method that co-elutes a degradant with the main peak can pass every SST criterion while overestimating potency.

SST is still essential. The FDA's OOS guidance notes that if standards injected through a run show the system is not working, data from the suspect period should not be used. The relationship runs one way: a validated method needs SST to be trusted on a given day, and a passing SST on an unvalidated method proves almost nothing about the result.

A strong answer covers

  • Validation proves fitness for purpose once
  • SST confirms performance on each run
  • SST uses standards and cannot test specificity in matrix
  • Failed SST invalidates data from the suspect period
  • Both are needed and serve different questions

Common mistakes

  • Treating a passing SST as evidence that a modified method is still valid.
  • Continuing to report sample results after a bracketing standard fails.
  • Setting SST criteria so loose they would never detect a real problem.