What to write in quality manual and audit plan

You asked how to document the use of an external company for internal audits, in both your quality manual and audit plan.

You need to meet the requirements of internal auditing, which do not stop you from using an external company to perform your internal audits. You also need not specify anything upfront about using an external company, as long as you plan your internal audits efficiently and they meet the purpose, along with suitable records. Remember that your audit programme is a planned schedule, it is not cast in stone; so if you have to change it to indicate the use of an external company, or include remote audit methodology, that is fine. In fact you should review teh programme based on risks and opportunities.

If you have an audit procedure, then in the manual you simply state that you have an audit program and the purpose of it. You then reference your procedure where you can choose if you wish, to state that although the responsibility is x person to maintain the programme, the lab may use external auditors, if and when considered necessary. More importantly, make sure that your contract with them and their work meets all ISO 17025 requirements, which is your responsibility, Eaxample are approving them as competent (External provided products and services, clause 6.6), ensuring confidentiality (clause 4.1) and impartiality (clause 4.2); clear communication in procuring their services for specified scope of work.

The following articles may be of interest

Checklist of ISO 17025 implementation steps at https://advisera.com/17025academy/blog/2019/08/28/checklist-of-iso-17025-implementation-steps/

The ISO 17025 toolkit procedure for audits, is available at hhttps://advisera.com/17025academy/documentation/internal-audit-procedure/, along with links to the five appendices related to the procedure. These include the Internal Audit Program, Internal Audit Checklist, Audit Nonconformity Report, Internal Audit Process Checklist and Internal Audit Report.