It is up to the laboratory to plan the internal program and define the scope of each audit as it suits operations. They should be based on risk, meaning if there are particular activities where nonconformances have occurred or there is pressure on the laboratory (increased risk), these activities should be included. There is no mandatory way to go about your internal audits; therefore, you can combine any activities and any assessments that you deem necessary. It is important to clearly define the audit scope and requirement criteria before you start. Then, as a competent auditor, you would proceed with the audit to the depth you deem necessary, raising findings against the specific criteria and referencing the ISO 17025 clauses.
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.