Document the procedure of participating in PT schemes and/or inter-laboratory comparison schemes and/or for organization of a rechecking/retesting system in an SOP. If the laboratory participates in a PT scheme the following procedures must be documented (see previous activity for an elaborate description of the different procedures):

• Procedure for ensuring that EQA samples are analyzed in the same way as routine samples.
• Reporting of results back to organizer of PT scheme.
• When the final report is received from the organizer of the PT scheme, checking of correctness of results, discussion of results with laboratory staff and follow-up of incorrect results with a problem analysis to formulate corrective actions, introduce controls and possible preventive actions in the routine procedures, including adaption of SOPs of these procedures.
• Monitoring if the problem is solved.

Ensure that the Plan-Do-Check-Act cycle is present in this procedure.

If the laboratory participates in an inter-laboratory comparison and/or has a rechecking/retesting system the same procedure as above must be followed; the laboratory must improve when incorrect results have been produced (the plan-do-check-act cycle must be followed).

If the laboratory organizes an inter-laboratory comparison itself this procedure must also be included in the SOP, including at least protocols for the following activities/items:

• Preparation of samples.
• Blinding of samples.
• Distribution of samples, including preparing of accompanying documents such as a guideline for reporting the results and a possible template for reporting of the results produced by participating laboratories.
• Analysis of results reported back to you (including an analysis of variance and identification of significantly deviating results).
• Drafting of the final report and sending this to all the participants.

If the laboratory has a rechecking/retesting system for a certain test the procedure for this also has to be included in the SOP.