ISO 17025 audit

You said:

I know "what" to look out for, but not "how" to or "who" to."

For clarity, the “what to look at for” are the audit criteria and in this case any ISO 17025 mandatory as well as additional laboratory defined requirements for calibrations. These are clause 6.4 and 6.5 requirements of ISO 17025.

To answer how to go about it and who the auditee is, you need to identify what documented information exists within the management system – all polices, plans, processes, and procedures which have been put in place. Using an ISO  17025 audit checklist firstly record whether mandatory documentation is in place. Secondly read through the documentation and determine how the laboratory documents their approach to support a requirement and or policy. Look for objective evidence to see that what is stated as done is in fact being done. In each case documentation should clearly define responsibilities. These are the personnel which should be interviewed during the audit (the auditee) and asked to provide evidence against the audit criteria. For example there is a mandatory need for calibration programme (ISO 17025 6.4.7) . Ask to see the programme, select a few items from the list and call for the calibration certificates as evidence of the programme working. Also look for evidence that the programme is reviewed and adjusted as necessary in order to maintain confidence in the status of calibration. For example, if there was a nonconformance raised or risk identified about lack of calibration or the external calibration interval, the programme should reflect that.  Find out if the laboratory specifies their review period and if so, assess whether that review period is complied with. If they do specify the review period, best practice is at least yearly or before / after management revied as required to keep the program active

The following will provide more information for you on Auditing and ISO 17025:
The White paper (free for download) How to perform an internal audit using ISO 19011 at https://info.advisera.com/free-download/how-to-perform-an-internal-audit-using-iso-19011
The article ISO 17025 technical internal audit: The basics at https://advisera.com/17025academy/blog/2020/11/10/iso-17025-technical-internal-audit-the-basics/
The ISO 17025 document template: Internal Audit Procedure at https://advisera.com/17025academy/documentation/internal-audit-procedure
The Five Internal Audit Procedure appendices Internal Audit Program, Internal Audit Checklist, Audit Nonconformity Report, Internal Audit Process Checklist and Internal Audit Report are available separately from the procedure link above; or included in the toolkit for preview and purchase.