4.2 External quality assessment
An
If participation in a formal PTS is not possible, assessment of quality may be achieved through a combination of within-country retesting/rechecking by a reference laboratory and internal QA with periodic external observation of practices and procedures by qualified personnel (WHO 2011a). In situations where a PTS for a specific test is not available, interlaboratory comparison to compare results and interpretation can be developed.
4.1 The PDCA model