Chapter 2: Quality Control of Urine and Saliva Analytes
Julie Day, Mira Doig & Isla Dougall
2.1 Introduction And Key Conclusions
This section describes the assay of analytes for the 2017 Scottish Health Survey ( SHeS) biological samples and the quality control and quality assessment procedures that were carried out during the survey period. Details of procedures used in the collection, processing and transportation of the specimens are available on request from ScotCen.
The overall conclusion for the data provided in this chapter is that methods and equipment used for the measurement of urine and saliva analytes produced internal quality control ( IQC) and external quality assessment ( EQA) results within expected limits. The results of the analyses for each of the main urine analytes and saliva cotinine levels were acceptable for the 2017 SHeS.
2.2 Analysing Laboratories
As in previous years, the Royal Victoria Infirmary ( RVI) in Newcastle upon Tyne was the analysing laboratory for the urine sample analyses in 2017. Salivary cotinine analysis of the 2017 samples was conducted by ABS Laboratories in Welwyn Garden City, Hertfordshire.
2.3 Samples Collected
2.3.1 Urine samples
A mid-flow spot urine sample was obtained from participants aged 16 and over taking part in the biological module. Urine samples were collected for analysis of sodium, potassium and creatinine. Participants were instructed to provide a sample of urine in the disposable collection beaker and then use the special urine collection syringe to draw up the sample. An instruction card was given to participants demonstrating how to use the syringe. Interviewers could also draw up the sample from the beaker if the participant preferred this. The urine collection syringe was then labelled and packaged ready for dispatch.
2.3.2 Saliva samples
A saliva sample was obtained from participants aged 16 and over. Saliva samples were collected for analysis of cotinine (a metabolite of nicotine that shows recent exposure to tobacco smoke). A saliva collection tube was used for this purpose. Participants were also offered the option to provide the saliva sample using a dental roll that they could saturate with their saliva before it was placed in the tube. The saliva tube was then labelled and packaged ready for dispatch.
2.4.1 Laboratory procedures for urine sample analyses
All analyses were carried out according to Standard Operating Procedures by State Registered Biomedical Scientists ( BMS) under the supervision of the Senior BMS. All results were routinely checked by the duty Biochemist.
A schedule of Planned Preventative Maintenance was used for each item of analytical equipment. These plans were carried out jointly by the manufacturers and the laboratories. Records were kept of when maintenance was due and carried out.
2.4.2 Laboratory procedures for saliva sample analyses
All analyses were carried out according to Standard Operating Procedures by analysts in a MHRA Good Laboratory and Good Clinical Practice ( GLP & GCP) accredited laboratory. All work is reviewed by the Laboratory & QA Manager.
A schedule of Planned Preventative Maintenance was used for each item of analytical equipment. These plans were carried out jointly by the manufacturers and the laboratories’ staff. Records were kept of when maintenance was due and carried out.
2.4.3 Urine sample analytical methods and equipment
Urinary sodium, potassium and creatinine analysis was carried out in the Blood Sciences Department at the RVI using a Roche Cobas 702 analyser. Urinary sodium and potassium were analysed using the indirect ISE method. Urinary creatinine was analysed using the Roche enzymatic Creatinine Plus method. Prior to the introduction of the Roche Cobas 702 analyser, the Roche Modular P analyser had been used in SHeS since April 2010, prior to this an Olympus 640 analyser was used. Any difference in results due to the changes in analytical equipment was minimal and not considered to be clinically significant. Details are available on request.
2.4.4 Saliva sample analytical methods and equipment
Saliva samples received at the RVI were checked for correct identification, assigned a laboratory accession number, and stored at 4°C. Samples were checked for details and despatched fortnightly in polythene bags (20 samples per bag) by courier for overnight delivery to ABS Laboratories, where cotinine analysis was carried out. This laboratory specialises in accurate measurement of low levels of cotinine and therefore takes special precautions to ensure no contamination by environmental tobacco smoke occurs.
The method of analysis used since the 2009 SHeS study is high performance liquid chromatography coupled to tandem mass spectrometry with multiple reaction monitoring ( LC-MS/MS), replacing the gas chromatography nitrogen phosphorous detection ( GC-NPD) method used in earlier SHeS studies  . The sample preparation prior to LC-MS/MS was liquid / liquid extraction. Samples were divided for analysis into batches of self-reported smokers and non-smokers and analysed either using a method with a high calibration range, 1 to 750 ng/mL for the self-reported smokers, or low calibration range 0.1 to 50 ng/mL for the non-smokers. A Tomtec Quadra was used to allow for the automation of some of the sample preparation. All methods were validated before use. If any of the samples from self-reported smokers gave a result below 1 ng/mL on initial analysis they were repeated in a low range batch. Similarly if any of the non-smoker samples gave a result above 50 ng/mL then they were repeated in a high range batch.
2.5 Internal Quality Control (Iqc)
2.5.1 Explanation of IQC
The purpose of internal quality control ( IQC) is to ensure reliability of an analytical run. IQC also helps to identify, and prevent the release of, any errors in an analytical run. IQC is also used to monitor trends over time.
For each analyte or group of analytes, the laboratory obtains a supply of quality control materials, usually at more than one concentration of analyte. Target (mean) values and target standard deviations ( SD) are assigned for each analyte. Target assignment includes evaluation of values obtained by the laboratory from replicate measurements (over several runs) in conjunction with target values provided by manufacturers of IQC materials, if available. The standard deviation and the coefficient of variation ( CV) are measures of imprecision and are presented in the tables. IQC values are assessed against an acceptable range and samples are re-analysed if any of the Westgard rules have been violated [2,3,4] . Internal quality assessment results are available from ScotCen Social Research upon request.
2.5.2 Urine samples
Two levels of IQC were used for urinary sodium, potassium and creatinine. Quality control samples were run at the beginning of the day and at regular intervals throughout the day.
2.5.3 Saliva samples
ABS laboratories ran 16 non-zero calibration standards for each batch of the low range assay (0.1-50 ng/mL) or high range assays (1-750 ng/mL). Six quality control ( QC) samples, two each at a set concentration to represent Low, Medium and High levels for the calibration range being used, were also analysed with each analytical batch. For the results from any analytical batch to be acceptable, four out of the six QCs must have a bias of no greater than ±15% with at least one from each QC level being within these acceptance criteria, and 75% of the calibration standards must have a bias of no greater than ±15% except at the lower limit of quantification where the bias must be no greater than ±20%.
2.6 External Quality Assessment ( EQA)
External quality assessment ( EQA) permits comparison of results between laboratories measuring the same analyte. An EQA scheme for an analyte or group of analytes distributes aliquots of the same samples to participating laboratories, which are blind to the concentration of the analytes. The usual practice is to participate in a scheme for a full year during which samples are distributed at regular frequency (monthly or bimonthly for example); the number of samples in each distribution and the frequency differ between schemes. The samples contain varying concentrations of analytes. The same samples may or may not be distributed more than once.
Samples are assayed shortly after they arrive at the laboratory. Depending on the frequency of distribution, there may be weeks or months in which no EQA samples are analysed. Results are returned to the scheme organisers, who issue a laboratory specific report giving at least the following data:
- Mean values, usually for all methods and for method groups;
- A measure of the between-laboratory precision;
- The bias of the results obtained by that laboratory.
EQA is a retrospective process of assessment of performance, particularly of inaccuracy or bias with respect to mean values; unlike IQC, it does not provide control of release of results at the time of analysis.
The Welsh External Quality Assessment Schemes ( WEQAS) are schemes in which the laboratories participate on a routine basis.
Monthly EQA results are available upon request from ScotCen Social Research.
2.6.2 Urine samples
The Blood Sciences (formerly Clinical Biochemistry) laboratory participates in the WEQAS scheme for the urine analytes (sodium, potassium and creatinine).
2.6.3 Saliva samples
There was no external quality control scheme available in 2017 for saliva cotinine analysis but ABS Laboratories participates in inter-laboratory split analyses to ensure comparable results. The latest International inter-laboratory study was published in 2009  .
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