acyl-CoA dehydrogenase deficiency (MCADD) andorganic acidaemiassuch as propionic
acidaemia caused by a deficiency of the enzyme propionyl-CoA carboxylase.16.2.3 Quality assessment procedures
In order to validate the analytical precision and accuracy of the biochemical tests
conducted by a clinical biochemistry department, the department will participate in
external quality assessment schemesin addition to routinely carrying outinternal
quality controlprocedures that involve the repeated analysis of reference samples
covering the full analytical range for the test analyte. In the UK there are two main
national clinical biochemistry external quality assessment schemes: theUK National
External Quality Assessment Scheme(UK NEQAS: http://www.ukneqas.org.uk) coordinated at
the Queen Elizabeth Medical Centre, Birmingham and theWales External Quality
Assessment Scheme(WEQAS: http://www.weqas.com) coordinated at the University Hospital
of Wales, Cardiff. The majority of UK hospital clinical biochemistry departments subscribe
to both schemes. UK NEQAS and WEQAS distribute test samples on a fortnightly
basis, the samples being human serum based. In the case of UK NEQAS the samples
contain multiple analytes each at an undeclared concentration within the analytical
range. The concentration of each analyte is varied from one distribution to the next.
In contrast, WEQAS distributes four or five test samples containing the test analytes
at a range of concentrations within the analytical range. Both UK NEQAS and
WEQAS offer a number of quality assessment schemes in which the distributed test
samples contain groups of related analytes such as general chemistry analytes,
peptide hormones, steroid hormones and therapeutic drug monitoring analytes.
Participating laboratories elect to subscribe to schemes relevant to their analytical
services.
The participating laboratories are required to analyse the external quality assessment
samples alongside routine clinical samples and to report the results to the organising
centre. Each centre undertakes a full statistical analysis of all the submitted results and
reports them back to the individual laboratories on a confidential basis. The statistical
data record the individual laboratory’s data in comparison with all the submitted data
and with the compiled data broken down into individual methods (e.g. the glucose
oxidase and hexokinase methods for glucose) and for specific manufacturers’ systems.
Results are presented in tabular, histogram and graphical form and are compared with
the results from recent previously submitted samples. This comparison with previous
performance data allows longer-term trends in analytical performance for each analyte
to be monitored. Laboratory data that are regarded as unsatisfactory are identified and
followed up. Selected data from typical UK NEQAS reports are presented in Table 16.4
and Fig. 16.3 and from a WEQAS report in Table 16.5.16.2.4 Clinical audit and accreditation
In addition to participating in external quality assessment schemes, clinical laboratories
are also subject toclinical audit. This is a systematic and critical assessment of the
general performance of the laboratory against its own declared standards and procedures637 16.2 Clinical measurements and quality control