UK External Quality Assessment Scheme Research Articles

Norethisterone interference in testosterone assays

This article describes three patients in whom measured serum testosterone concentrations were found to be artifactually high due to interference from norethisterone medication. This interference was investigated further by distributing samples containing norethisterone through an external quality assessment scheme. Serum samples containing different concentrations of norethisterone were distributed to participants in the UK external quality assessment scheme (UK NEQAS) for female testosterone in order to assess the degree of interference from norethisterone in different commercially available immunoassay and liquid chromatography-tandem mass spectrometry methods for measurement of testosterone. The results have shown that apparent serum testosterone concentrations in excess of 5 nmol/L may be obtained using the Roche E170 Modular immunoassay method for samples collected from patients taking norethisterone medication and this interference can be reproduced by adding norethisterone to serum samples. Although the biggest interference is seen with the Roche system, there is a small effect in the Siemens ADVIA Centaur assay and some of the other immunoassays may also be affected to a much lesser extent. Norethisterone does not interfere in testosterone measurements obtained by liquid chromatography-tandem mass spectrometry.

Instability of mercury in specimens of human urine for external quality assessment

An under-recovery of inorganic mercury added to urine and a wide range of results is observed in quality assessment schemes (EQAS) for trace elements. Further- more, the under-recoveries are inconsistent suggesting features associated with the urine matrix may make the mercury unavailable for measurement. To investigate the instability of mercury in urine the following experiments were set up: (1) a sample of Hg 2? in water with various 'stabilizers' added was sent to UK external quality assessment scheme participants. (2) Urine was collected from volunteers who also completed a 3-day food diary. Hg, Ca, Mg, Se, uric acid, phosphate, creatinine, reducing substances and protein were measured. Inorganic mercury was spiked into the urine, stabilizers were added and the mercury determined following storage. The results con- firmed under-recovery of mercury in association with the urine matrix. Further investigations of how urinary com- ponents affect the measurement of mercury are necessary.

The bleeding time: current practice in the UK.

A questionnaire survey of current practice in the bleeding time test has been undertaken by the UK External Quality Assessment Scheme in blood coagulation. Completed returns have been received from 358 centres. Most centres (88.5%) perform bleeding times and of these the Ivy test is the most commonly performed. Only 13.6% perform the Duke method. Templates are used to control the procedure by approximately half of the hospitals. There is considerable variability in the type and depth of incision and interpretation of the endpoint. The upper limit of normality not unexpectedly differs considerably between the centres with both Ivy and Duke methods. The use of a commercial template method, 'Simplate', provides a measure of agreement amongst the group of hospitals using this instrument but it remains to be established whether this is the most reliable procedure. In the interim, gross discrepancies in technique or interpretation should be corrected in the light of the findings of the survey.

Production and certification of four frozen human serum certified reference materials containing creatinine and electrolytes

This paper describes the preparation, analysis and certification of four frozen human serum certified reference materials (CRMs) containing creatinine and the electrolytes calcium, lithium, magnesium, potassium and sodium. These materials have been prepared to give concentrations of these analytes that cover the currently accepted analytical range. The analysis of the materials for certification purposes has been carried out using methodology traceable to primary standards, and which is acceptable as a reference method. The certification methods include liquid chromatography-mass spectrometry (LC-MS) with exact-matching isotope dilution calibration (EM-IDMS) for creatinine, inductively-coupled plasma optical emission spectroscopy (ICP-OES), ICP-MS and isotope-dilution inductively-coupled plasma mass spectroscopy (ID-ICP-MS) for the electrolytes. The uncertainties estimated for these certified values include a component from the characterization measurements, as well as contributions from possible inhomogeneity and long-term instability. The certified values have been corroborated by measurements obtained in a major UK External Quality Assessment scheme, which have, with the exception of the determination of creatinine at a particularly low concentration, given excellent agreement. The materials are intended for use by pathology laboratories and manufacturers of in vitro diagnostic (IVD) kits for validation of existing routine methodology to a traceable standard, which will promote harmonization between the different methods, instruments and IVD kits used in these laboratories.

Normal growth hormone response to the 75 g oral glucose tolerance test measured by immunoradiometric assay.

Estimation of plasma growth hormone (GH) during a 50 g oral glucose tolerance test (OGTT) is widely used in the investigation of suspected acromegaly and in monitoring its response to treatment. A plasma GH of < 2 mUlL measured in terms of International Reference Preparation (I RP) 66/217 by radioimmunoassay (RIA) is considered normal in the majority of UK labora­ tories, although data from the UK External Quality Assessment Scheme reveal that cut-offs as low as I mUj l.; and as high as 10mUIL, are used. Two developments suggest a need for reapprai­ sal of the normal GH response. Firstly, since 1982 the 50 g OGTT has been superseded by a 75 g OGTT in the diagnosis of diabetes mellitus, I and it would seem desirable to standardise the pro­ cedure for both conditions. Secondly, the intro­ duction of sensitive immunoradiometric assays (IRMA) for GH has made it possible now to measure levels that are below the detection limit of most RIA This short study was performed, therefore, to define the normal plasma GH response measured by IRMA during a 75 g OGTT. The normal subjects comprised 16 men and 8 women (mean age 28·6 years, range 21-48) who did not abuse alcohol and had no clinical evidence of pituitary, liver or renal disease. They were fasted overnight and rested in the sitting position for 45 min prior to insertion ofa Venflow catheter in the antecubital fossa at - 30 min. Following two basal samples, at -IS and 0 min, 75 g of glucose in 200 mL water (freshly prepared) was given orally at 09.00 h. Blood was collected at 30 min intervals for ISO min into heparinised tubes on ice, and the plasma assayed for GH using the Boots-Celltech Sucrosep kit (Boots-Celltech Diagnotics Ltd, Slough, Bucks, UK), and glu­ cose. Samples from individual patients were all

Oestradiol assays: applications and guidelines for the provision of a clinical biochemistry service.

This paper reports on the provision of a clinical biochemistry service for serum oestradiol. The pathophysiology and recognised applications of oestradiol assays are discussed and the current availability of assay reagents and methodologies reviewed. Data are presented on the analytical performance of assays for serum oestradiol in the UK External Quality Assessment Scheme (UKEQAS) and general guidance is offered to laboratories providing a diagnostic service for this analyte.

Factors associated with the quality of laboratory performance in the United Kingdom external quality assessment scheme for serum growth hormone

A search was made for associations between poor performance in the UK External Quality Assessment Scheme (EQAS) for serum growth hormone (GH), and a range of factors including assay method, laboratory workload and staffing, and Internal Quality Control (IQC) procedures. On the basis of the factors identified as being associated with poor performance we recommend the following. 1. Laboratories using RIA for GH should routinely analyse samples at two dilutions and report a mean result. 2. The use of 125I-GH which is 5 or more weeks old should be avoided. Tracer should also be chromotographed to remove aggregate before use. 3. Laboratories using RIA should avoid using a standard curve which covers too wide a range of concentration; a curve midpoint (ie GH concentration to reduce the zero standard binding by 50%) of about 8 mU/l or less is probably acceptable. 4. It should be noted that high workloads present a risk of some loss in quality of performance. 5. An experienced member of staff other than the assayist should be responsible for checking IQC data. 6. Laboratories which do not have the resources to maintain fully their own RIA as outlined above should carefully consider use of an unbiased, precise IRMA. The UK EQAS has identified two assays (Boots-Cell-tech Sucrosep, NETRIA) that appear to meet these criteria [2]. The above observations may also be relevant to immunoassays for other peptide hormones.

The oral glucose tolerance test--an assessment of the quality of its performance.

By means of a questionnaire, an attempt was made to assess the quality of performance and interpretation of the oral glucose tolerance test by laboratories participating in the UK External Quality Assessment Scheme for Clinical Chemistry. The results showed a general awareness of current recommendations in terms of both protocol for the test and criteria for interpretation of results, but some deficiencies were observed in both these areas and in some case deviations in protocol may have been sufficient to invalidate comparison of results with currently recommended criteria for interpretation of the test.

Assays for follicle stimulating hormone and luteinising hormone: guidelines for the provision of a clinical biochemistry service.

The measurement of serum follicle stimulating hormone (FSH) and luteinising hormone (LH), together with the appropriate sex steroid, is of great value in the investigation of delayed and precocious puberty, hypogonadism, subfertility, polycystic ovarian disease and hypothalamic-pituitary disorders. Dynamic function testing of the hypothalamic-pituitary-gonadal axis should be restricted to a few defined situations. Sequential LH measurements, either in serum or in urine, may be used to time ovulation during artificial insemination or in vitro fertilisation programmes. No special precautions are necessary when sampling for FSH and LH measurement; serum is preferred to plasma and should be stored frozen before assay. Aliquots of timed urine specimens of known volume should be stored frozen without preservative. Gonadotrophin results should be available within 2-3 weeks; laboratories unable to meet this schedule are advised to send their samples to a Regional Centre for assay. Reagents for the radioimmunoassay of FSH and LH are readily available, and standard techniques have been developed for their use. Laboratories using 'in-house' methods should pay particular attention to the matrix used for preparing standard solutions, the purification of radioligands and the optimisation of the separation system. Low cost matched reagents of proven performance are available in kit form from the Chelsea Hospital for Women; several commercial kits are also available, although few are widely used in the UK. The overall performance of laboratories in the UK External Quality Assessment Scheme (EQAS) for FSH and LH has remained steady for several years. Of the 130 participants, only about 15% in each scheme have 'good' performance (cumulative bias less than 10%, plus cumulative variability of bias less than 10%), whilst a similar proportion have 'unacceptable' performance (cumulative bias greater than 20% and/or cumulative variability of bias greater than 25%). The remaining 70% of laboratories have 'adequate' performance but are at risk of producing results that are clinically misleading. Within any one method group, the performance of FSH and LH assays are closely related. Optimal assay performance depends upon sensible laboratory management to ensure skilled operators, a regular programme of reagent/kit renewal, comprehensive internal and external quality assessment, and attention to detail in all aspects of gonadotrophin assay. The working range of each individual assay should be defined and no absolute result reported from outside this range.(ABSTRACT TRUNCATED AT 400 WORDS)

Assays for prolactin: guidelines for the provision of a clinical biochemistry service.

This paper summarises the views of the authors on the provision of a prolactin assay service. We discuss the pathophysiology of prolactin secretion and the clinical indications that arise from that. We cover the rather complex issue of the definition of normal and elevated prolactin levels. From these considerations, certain guidelines on the analytical performance of prolactin assays and their provision in a clinical biochemistry service are given. The extent to which currently available methods and performance as revealed by the UK External Quality Assessment Scheme (EQAS) match these guidelines are described and certain conclusions are reached. Finally, probable future developments are briefly discussed. The main conclusions and recommendations are as follows: Reagents of appropriate quality are available to enable prolactin immunoassays to be provided in UK clinical biochemistry laboratories. These are provided either separately or in the form of kits from both commercial and NHS sources. There is no requirement for individual laboratories to undertake their own antiserum production or prolactin iodination. Acceptable performance (as defined using internal QC procedures and the UK EQAS) is achievable using these reagents/kits, although one commercial kit shows a consistent marked negative bias. Reference ranges, including 'normal ranges', show considerable between-centre variability. Many centres have not established their own ranges, even those using in-house methods. Reference ranges for use in clinical biochemistry laboratories are proposed in this report. Some general guidance on the provision of a prolactin service is given, although this does not differ in principle from that appropriate for other peptide hormone analytes. There is no evidence that centres with small workloads perform any worse than average, although it may be more cost-efficient for such centres to send the samples elsewhere. As with other peptide analytes, non-isotopic immunometric methodology is likely to replace current radioimmunoassay methods in the near future.

External quality assessment of serum enzyme activity assays and the effect of calibration on interlaboratory concordance.

The design and results of a UK external quality assessment scheme for six enzymes are described, from 21 surveys over a period of 7 years. Improvements in interlaboratory agreement and the adoption of reliable methods are documented. The potential of enzyme calibration materials in further improving numerical concordance between laboratories using different assay conditions, including temperature, is demonstrated and discussed.

Improved performance of plasma gonadotrophin assays using common reagents and assay protocols: evidence from the UK External Quality Assessment Scheme.

Radioimmunoassay kits prepared in the Chelsea Hospital for Women for follicle stimulating hormone (FSH) and luteinising hormone (LH) have been used in 26 UK laboratories for over 2 years. Data from the UK External Quality Assessment Schemes for FSH and LH have been used to provide an independent assessment of the performance of these kits over a 12-month period. For both analytes, users of the kits were found to have: a low variability of the bias, implying good within-laboratory, between-assay precision; a lower between-laboratory, within-sample geometric coefficient of variation than users of 'own' methods, implying better between-laboratory agreement; method bias that did not differ significantly from laboratories using 'own' method protocols. This survey indicates that a non-commercial organisation can produce immunoassay kits that improve the quality of FSH and LH assays generally available.