Accreditation

The Clinical Biochemistry Department is a UKAS Accredited medical laboratory No.8055

For further information on the Accreditation schedule, please click here or on the link https://www.ukas.com/wp-content/uploads/schedule_uploads/00007/8055%20Medical%20Multiple.pdf 

In order to ensure the quality of our service the department participates in a number of external quality assurance schemes (EQA) including:

United Kingdom National External Quality Assessment Service (NEQAS)

Wales External Quality Assessment Scheme (WEQAS)

The department also uses internal quality control processes for it's examination procedures to ensure the day-to-day validity of results.

If you would like more detailed information on our performance for a particular analyte, please contact the department on extention 8455.

Uncertainty of measurement

Medical testing gives results that are subject to a degree of variability. This can be due to factors such as poor specimen collection, delays in transport, clerical and reporting errors. It is important to identify and minimise these factors.

Analytical error
 
The laboratory regularly assays quality control materials (IQC) in order to ensure the performance of our assays on a day-to-day basis. The variability of IQC results over time allows us to quantify the Analytical Error (AE) of an assay – that is to say the range of acceptable results at particular, clinically relevant, assay levels.
Each assay is also compared to the results from other national and international laboratories, this demonstrates any bias that our method shows against other methods (including a ‘reference method’) in the error calculation.
AE is expressed as a percentage. Thus we can be sure (with 95% certainty) that any result is within +/-1.96 x result x AE (%). 
Consider that vital test - the serum rhubarb. Assuming a ‘true’ value of 10 with an AE of 5%: 
Result   = 10 ± 1.96 x 10 x 5 / 100
            => 10 ± 0.98  
I.e. for a serum rhubarb of ‘10’ any result between 9.02 and 10.98 is analytically correct. 

Reference change values 

Reference change values (RCV) are useful in serial monitoring of patients. Changes in a patient’s results may be due to any of the following factors:
◦    Pre-analytical variation (e.g. specimen collection and storage)
◦    Analytical variation (AE as described above)
◦    Within-subject biological variation
◦    Variation due to pathological changes
 
The laboratory uses written procedures and protocols to limit the pre-analytical variation, and this is not normally included in RCV calculations.
RCV are based on the sum of the AE and within-subject variation. Hence, a change in an assay value greater than the RCV is indicative of a real change in the assay result, often an improvement or deterioration in a disease process.
RCVs (like AE) are expressed as a percentage of the result. So we can be sure (with 95% certainty) that an :- 
assay result >  ±2.77 x previous result x RCV / 100  
is outside the expected limits of normal biological variation (i.e. is a real change from the previous result). 
 
For commonly monitored parameters, the laboratory will quote an RCV in the test information page and for other particular assays (e.g. HbA1c) indicate on the report when a change is significant (i.e. outside the RCV). 
 
For more information on Uncertainty of Measurement please contact:
Clinical Biochemistry Operational Manager – Jamie West (ext 8462)
Or email: peh-tr.chemimm@nhs.net