may be in terms of arbitrary units or IQC o.d./Cut-off o.d.). Westgard rules define specific performance limits and are designed to detect both random and systematic errors. Of the six commonly used Westgard rules, three are warning rules and the other three are mandatory rules. The latter, if broken should result in the rejection of the test run. Warning Rules 1. The control value exceeds the mean by 2 s.d. (p<.005) 2. Two consecutive values exceed the target value on the same side of the mean by 2 s.d. This may indicate the presence of systematic errors. 3. Four consecutive control values exceed the same limit. This again indicates the possible presence of
Quality AssessmentQuality assessment is a means to determine the quality of results. It is usually an external evaluation of alaboratory's performance that relies on incorporating proficiency panels of well-characterized sera into thetesting routine. External quality assessment (EQA) is now recognized as an essential component ofquality assurance and is the only means to give the laboratory manager an independent means of ensuringthat his routine quality control is adequate and effective. The National External Quality AssessmentScheme (NEQAS) is administered by the PHLSThe following are distributed under the NEQAS scheme:1. Hepatitis B serology2. HIV serology3. Rubella serology (IgM and IgG)4. General virus serology5. Virus isolation6. Electron microscopyIt is important for the participating laboratory to treat NEQAS specimens in the same manner as normalroutine specimens. Rubella IgM and HIV currently lack national reference preparations, as opposed torubella IgG and HBsAg. Occasionally, more difficult specimens than usual are distributed as "education"material, such as those containing very low levels of HBsAg or anti-HIV. Scores are not normallyallocated for this type of specimen, but participants may find it useful to compare their results with thoseof their peers.The scoring system for NEQAS is as follows2 fully correct report1 partially correct report e.g. partial identification of a virus or an equivocal serologicalresult0 erroneous result which would not have serious clinical consequences e.g. false negativerubella IgG-1 erroneous result which would have serious clinical consequences, e.g. false negativeHBsAg or anti-HIV It is highly desirable for the laboratory itself to have an internal quality assessment program, wherebyanonymous clinical samples are submitted to the laboratory. An internal quality assessment scheme can be
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- Fall '12
- Medical laboratory