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The difference between calibration and qualification of an instrument

30 August 20266 min read

In breve

Calibration compares the instrument against a metrological reference and quantifies its accuracy; qualification demonstrates with documented protocols that the instrument or equipment is well installed and fit for the intended use (IQ/OQ/PQ). The first concerns the measurement, the second the suitability: in GMP both are needed and they integrate.

Two different questions

Calibration and qualification answer distinct questions:

  • Calibration: "how accurate is the measurement of this instrument compared to a traceable standard?" It is a metrological comparison that produces a deviation and an uncertainty, with an As Found / As Left outcome.
  • Qualification: "is this instrument (or equipment) fit for the intended use, correctly installed and operating as it should?" It is a documentary path (DQ/IQ/OQ/PQ) that generates evidence for the audit.

In short: an instrument can be perfectly calibrated but not qualified for use in that process, and conversely a piece of equipment can be qualified but contain instruments whose calibration has expired. They are controls on different levels.

Where they meet

The two worlds meet at at least two points:

  1. In the IQ, among the checks there is the calibration status of the critical instrumentation on board the equipment: you do not qualify a piece of equipment whose measuring instruments are not calibrated and traceable.
  2. In the reference instruments used during the qualification tests (for example the data loggers of a thermal requalification): they must in turn be calibrated, with traceability guaranteed through ACCREDIA-accredited laboratories.

A table to fix the ideas

| | Calibration | Qualification | |---|---|---| | Question | How accurate is the measurement? | Is the instrument/equipment fit for use? | | Output | Certificate with deviation and uncertainty | Approved DQ/IQ/OQ/PQ protocols | | Reference | Traceable standard (metrological chain) | URS, Annex 15, GAMP5 | | Frequency | Risk-based interval | At installation + requalification for modification/periodic | | Typical outcome | As Found / As Left, Out of Tolerance management | Compliant / deviation |

Why the confusion is costly

Treating the two terms as synonyms leads to concrete errors: thinking that "calibration is enough" for a new piece of equipment, or that a qualification replaces the management of calibration intervals. In an audit, this confusion emerges immediately. A mature GMP system keeps the two processes distinct but connected: calibration management feeds qualification, and qualification presupposes calibrated instruments.

Domande frequenti

Are calibration and 'taratura' the same thing?

In practice yes: in current Italian usage 'taratura' and 'calibrazione' are used as synonyms to indicate the comparison of the instrument against a metrological reference. The relevant distinction in GMP is the one between calibration and qualification, not between the two words for calibration.

Must a qualified instrument also be calibrated?

Yes. Qualification demonstrates suitability and correct installation, but if the instrument performs critical measurements it must be calibrated and kept in a calibration status with a justified interval. Verification of the calibration status is in fact part of the IQ.

Is the qualification of the equipment enough, or are the calibrations of the on-board instruments also needed?

Both are needed. The qualification of the equipment does not exempt from the management of the periodic calibrations of the critical measuring instruments installed: they are controls on different and complementary levels.

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