A recommended scheme for the evaluation of kits in the clinical laboratory

Validation of assembled nucleic acid-based tests in diagnostic microbiology laboratories

Medical microbiology and virology laboratories use nucleic acid tests (NAT) to detect genomic material of infectious organisms in clinical samples. Laboratories choose to perform assembled (or in-house) NAT if commercial assays are not available or if assembled NAT are more economical or accurate. One reason commercial assays are more expensive is because extensive validation is necessary before the kit is marketed, as manufacturers must accept liability for the performance of their assays, assuming their instructions are followed. On the other hand, it is a particular laboratory's responsibility to validate an assembled NAT prior to using it for testing and reporting results on human samples. There are few published guidelines for the validation of assembled NAT. One procedure that laboratories can use to establish a validation process for an assay is detailed in this document. Before validating a method, laboratories must optimise it and then document the protocol. All instruments must be calibrated and maintained throughout the testing process. The validation process involves a series of steps including: (i) testing of dilution series of positive samples to determine the limits of detection of the assay and their linearity over concentrations to be measured in quantitative NAT; (ii) establishing the day-to-day variation of the assay's performance; (iii) evaluating the sensitivity and specificity of the assay as far as practicable, along with the extent of cross-reactivity with other genomic material; and (iv) assuring the quality of assembled assays using quality control procedures that monitor the performance of reagent batches before introducing new lots of reagent for testing.

The effects of sulphasalazine and its metabolites on prostaglandin production by human mononuclear cells

Although it has been proposed that sulphasalazine (SASP) and its metabolite 5-aminosalicylic acid (5-ASA) act therapeutically by inhibiting production of vasoactive and immunoregulatory prostaglandins (PGs), in previous in vitro studies these drugs have both inhibited and promoted PG production. This study demonstrates that SASP and 5-ASA promote or inhibit peripheral blood mononuclear cell PG production depending upon the PG measured, the concentration of the drug, and whether the cells were stimulated. Sulphapyridine, the other constituent of SASP, only inhibited production. At high concentrations of SASP and 5-ASA the viability of mononuclear cells was reduced. The enhancement of PG production and toxicity was greater with SASP than 5-ASA, while the PGs most affected by SASP were not those most affected by 5-ASA. Thus, in vitro SASP may possess properties other than those of 5-ASA and this may explain the different therapeutic properties of these two compounds.

Multicenter evaluation of five commercial rubella virus immunoglobulin G kits which report in international units per milliliter

In a multicenter study, the consistency of international units expressed by five commercially available rubella virus immunoglobulin G kits was evaluated. The linearity and within-run and between-run precision were determined for each kit. All kits demonstrated good linearity and had within-run and between-run precision coefficients of variation ranging from 5.1 to 21.7% and from 9.5 to 51.0%, respectively. To compare the international units expressed, the results from 40 samples tested in duplicate were compared with the results of a reference enzyme immunoassay calibrated with World Health Organization international standard serum and a hemagglutination inhibition test. The results of the kits were plotted against those of the reference tests, and linear regression analysis was applied. The Pearson correlation coefficient ranged from 0.64 to 0.75 when the commercial kit results were compared with those of the reference enzyme immunoassay, indicating only a moderate degree of correlation. Therefore, the international units expressed by the commercial kits are insufficiently consistent to be of practical use in diagnostic clinical microbiology.

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)

An evaluation of 13 commercial kits for the measurement of testosterone in serum and plasma

An evaluation has been carried out of 13 commercial testosterone kits. The within- and between-assay imprecision was found to be unsatisfactory for some kits. Sensitivity and linearity were acceptable for all the kits but several showed concentration-dependent biases to the ALTM or GCMS values. The occurrence of anomalous results and changing performance characteristics of some of the direct kits is also presented.

Colorimetric enzymatic measurement of serum total 3 alpha-hydroxy bile acid concentrations without extraction

A new method for the simpler colorimetric assay of serum total 3 alpha-hydroxy bile acid concentrations without prior extraction has been investigated. The lowest concentration that could be reliably measured was 3 mumol/l and the results obtained were in agreement with those obtained using extraction and the spectrofluorimetric enzymatic assay (y = 1.007x - 1.86, r = 0.99, n = 36). Results for 20 normal sera collected after an overnight fast were 6.2 +/- 5.1 mumol/l (mean +/- SD) and in 20 normal plasma randomly collected were 4.9 +/- 4.2 mumol/l. This new assay is comparable in specificity and sensitivity to the older spectrofluorimetric enzymatic assays and convenient for routine use.

Use of a recommended evaluation scheme in the assessment of a new digoxin radioimmunoassay kit

A new digoxin radioimmunoassay kit with a magnetizable solid-phase antibody was assessed using a recommended evaluation scheme. The kit was found to have acceptable performance characteristics, and the results are presented in the format recommended in the evaluation scheme to maximize comparability with data from other such studies. While the evaluation protocol was found to be generally workable and valid, modifications are suggested to enhance its applicability to an immunoassay system.

Determination of total and direct bilirubin in plasma by means of a bichromatic method on a centrifugal analyser

A bichromatic method is described for the determination of both total and direct-reacting bilirubin using a miniature centrifugal analyser. Bilirubin was coupled with diazotised sulphanilic acid in strongly acidic reaction conditions, and sodium dodecyl sulphate was used as accelerator for the measurement of total bilirubin. The inclusion of dyphylline as a haem-binding agent greatly reduced interference, even in the presence of extreme haemolysis. The method was shown to be precise, to be more sensitive and less affected by haemolysis than alternative methods, and to allow the estimation of total and direct bilirubin within the same run.