Use of serum from patients with polycythaemia or haemochromatosis for laboratory external quality assurance exercises

Some External Quality Assessment Schemes (EQAS) require large volumes of human serum. During a one year period, 595 units of blood were obtained from 87 patients with haemochromatosis and polycythaemia, who underwent therapeutic venesection at the Edinburgh and South East Scotland Blood Transfusion Service. Serum from 59% of these donations was used in the EQAS for peptide hormones and related substances. The cost of the serum collection was 109 pounds/litre, but was only 33 pounds/litre of serum if the cost of the actual venesection was excluded. Results from tests on the sera were satisfactory in a variety of immunoassays for several different hormones. EQA schemes with requirements for large volumes of serum should consider therapeutic venesection as a cost effective means of obtaining serum.

Does dietary magnesium modulate blood lipids?

In a randomized, single-blind, controlled study (400 patients aged 25-63 yr; 374 males, 26 females), 206 subjects were administered a magnesium-rich diet, and 194 subjects their usual diet, for 6 wk. Age, sex, body weight, hypertension, hyperlipidemia, smoking, obesity, diuretic therapy, and diabetes were comparable between the two groups, as were laboratory data at entry to the study. Intervention-group A received a significantly higher amount of dietary magnesium and potassium compared to group B, which received its usual diet. After 6 wk, there was a significant fall in total serum cholesterol (228.5 +/- 46.2 mg/dL), LDL cholesterol 146.5 +/- 75.5 mg/dL), and triglyceride (143.8 +/- 40.5 mg/dL) in group A compared to serum cholesterol (242.5 +/- 58.2 mg/dL), LDL cholesterol (157.0 +/- 78.4 mg/dL), and triglyceride (156.5 +/- 60.0 mg/dL) at entry to study, but no such changes in group-B subjects. HDL cholesterol showed a marginal mean decrease of 0.8 mg/dL in group B and a 2.5 mg/dL increase in group A. The changes in blood lipids were consistent with an increased intake of magnesium and with a rise in serum levels. Although a general blood-lipid-reducing effect of such a diet cannot be excluded, it is possible that dietary magnesium may have contributed to the reduction of total serum cholesterol, LDL cholesterol, and triglyceride, and the marginal rise in HDL cholesterol. More studies with longer follow-up periods are needed to confirm this observation.

Progress in immunoassays for serum prolactin: evidence from the UK External Quality Assessment Scheme (EQAS) 1980-1989

The quality of serum prolactin assays routinely performed by UK laboratories has been monitored in an external quality assessment scheme (EQAS) over a 10-year period, during which participation in the EQAS increased three-fold, and considerable changes in methods and standardization were introduced. The all-laboratory mean was used as the sample target value, and proved to be stable and accurate. Overall between-laboratory agreement in the clinically important range improved from a geometric coefficient of variation (GCV) of 25% to 14%. This appears to reflect the increased use of kits in place of 'in-house' assays, the more widespread availability of international standards and the absence of any marked differences in bias between the commonly used methods. Published guidelines on the clinical interpretation of prolactin values should, therefore, be widely applicable. The EQAS data indicate that, in general, the quality of performance of prolactin assays is adequate for their clinical application.

Progress and problems in immunoassays for serum pituitary gonadotrophins: evidence from the UK external quality assessment schemes, (EQAS) 1980-1988

Trends in the quality of assays for serum gonadotrophins performed by laboratories in the UK EQAS during the 1980s are reviewed, with particular reference to the effects of the recent introduction of immunometric assays (IMA) as an alternative to radioimmunoassay (RIA). IMA gave results which were on average 17% higher than RIA for FSH, and 33% lower for LH. These bias characteristics were not entirely accounted for by differences in assay standardisation, but appeared to reflect the different isoforms of the hormones detected by the monoclonal antibodies used in the IMA. Between-laboratory agreement remained, consequently, unsatisfactory overall (geometric coefficient of variation, GCV, 20-30%), although good within method groups (GCV 10%). IMA were less vulnerable to non-specific background interference than many RIA, and could avoid interference from HCG. Some IMA were, however, vulnerable to interference from heterophilic antibodies in patients' sera. The differences between RIA and the various IMA in numerical values reported, and in their vulnerability to interferences underline the need for care in interpreting assay results.

Quality of performance of assays for serum growth hormone in the United Kingdom (UK): evidence from the UK external quality assessment scheme, 1980-1987

The performance of laboratories in the UK External Quality Assessment Scheme for growth hormone (GH) during the years 1980 to 1987 is reviewed. The number of participating laboratories has increased steadily and is at present 67; about one half use immunoradiometric assay (IRMA) kits and the use of such kits is increasing at the expense of 'in-house' radioimmunoassays (RIAs). The consensus mean, which is used as the target value for assessing performance, has remained accurate and reproducible against this changing background. The between-laboratory geometric coefficient of variation has remained at about 18% during the period reviewed, revealing unsatisfactory between-laboratory agreement. This is in part due to poor within-laboratory performance in a small proportion of laboratories but it is also due to the negative bias of some IRMA kits. Most IRMA kits do appear, however, to provide marginally better within-laboratory precision than RIA, and are less vulnerable to non-specific interference. The laboratory interpretation of results was assessed from time to time, and was generally satisfactorily performed. In an attempt to identify the causes of poor performance, a detailed survey of assay methods and laboratory practice has been carried out; the results are described in an associated report [1].

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 chromatographed to remove aggregate before use. 3. Laboratories using RIA should avoid using a standard curve which covers too wide a range 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 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-Celltech Sucrosep, NETRIA) that appear to meet these criteria [2]. The above observations may also be relevant to immunoassays for other peptide hormones.

Quality of performance of assays for maternal serum alphafetoprotein in the United Kingdom: evidence from the UK external quality assessment scheme 1980-87

Between-laboratory agreement in the UK EQAS for maternal serum alphafetoprotein has improved steadily since 1976 and the geometric coefficient of variation is now 8 to 9% at levels of 50 to 150 kU/L. The use of a common standard and commercial assay kits appear to have contributed to this trend. Within-laboratory performance is also generally good, about 50% of participants maintain a bias of less than 5%, together with a scatter of the bias of less than 10%. These data indicate that the quality of assay performance is adequate for the requirements of screening programmes for open neural tube effects. The improvement in laboratory performance is such that between-laboratory agreement is better expressed in kU/L than as multiples of the median. Errors in interpretation of clearly normal or abnormal results appear to be rare (0.4%), and contribute little to overall false positive and negative rates. However, they assume significance as most are due to avoidable errors.

Does treatment with bromocriptine influence the course of hyperprolactinaemia?

Twenty-two women with hyperprolactinaemia without evidence of microadenoma, either untreated (n = 3), treated with bromocriptine for a total of less than 1 year (n = 12), or treated with bromocriptine for a total of more than 1 year (n = 7) were followed up by retrospective case-note review for at least 53 months. More than 50% of the women showed a fall in serum prolactin concentrations by more than 40% over the period of follow-up. The occurrence of a fall did not appear to be related to either length of treatment with bromocriptine or to the occurrence of pregnancy. Some women elected to remain untreated, despite symptoms, in preference to taking tablets and having to use contraception. The wisdom of leaving patients untreated in the light of these findings is discussed.

Thyroid function and endocrine abnormalities in elderly patients with severe chronic obstructive lung disease

Serum pituitary and thyroid hormones, testosterone, and the response of pituitary hormones to thyrotrophin releasing hormone were measured in 20 inpatients (mean age 68, range 42-81 years) with severe chronic obstructive lung disease and in 15 control convalescent inpatients (mean age 73, range 57-83 years) who had normal respiratory function. No significant differences were found in total and free thyroid hormone concentrations and basal concentrations of thyrotrophin, growth hormone, and prolactin; and their increments after injection of thyrotrophin releasing hormone were similar in patients with chronic obstructive lung disease, and control patients. Three patients with chronic obstructive lung disease, however, had no thyrotrophin responses to thyrotrophin releasing hormone. In men, low testosterone concentrations were found both in patients with chronic obstructive lung disease and in controls. Luteinising hormone concentrations were higher in men with chronic obstructive lung disease (p less than 0.02), whereas concentrations of follicle stimulating hormone in the two groups were not significantly different. There was no significant correlation between arterial blood gas tensions and these hormone measurements. General effects of age and illness may be more important than direct effects of hypoxia in determining hypothalamic-pituitary function in elderly patients with chronic obstructive lung disease.

Laboratory and diagnostic performance of a coated well immunoradiometric assay for serum thyrotrophin

A new, coated well immunoradiometric assay (IRMA) for thyrotrophin (TSH) in serum has been evaluated with a view to its use as a first-line test of thyroid function. The Amerwell TSH IRMA is simple, rapid to perform (2.5 h) and the assay sensitivity was 0.07 mU/L with a working range (intra-assay CV less than 10%) of 0.3-100 mU/L. The mean inter-assay CV was 6.6% for TSH concentrations of 0.30-30.7 mU/L. The method compared favourably with an in-house TSH radioimmunoassay and an alternative commercial IRMA. In consecutive referrals to a thyroid clinic all patients with overt hyperthyroidism (n = 103) had undetectable TSH concentrations and in those with subclinical hyperthyroidism (n = 14). TSH was undetectable in 10 and below the reference range in four. The 95% confidence interval for 63 euthyroid serum samples was 0.36-4.3 mU/L. All hypothyroid patients (n = 20) had increased TSH concentrations. TSH concentrations in pregnancy did not differ significantly from euthyroid TSH values. From 1916 routine tests, 13 undetectable TSH values were found in which thyroid hormone levels were normal and the patients had no known thyroid disorder. The assay appears suitable as a first-line test of thyroid function, but further assessment in a routine laboratory setting is required.

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)

Relationship between pituitary and other target organ responsiveness in hypothyroid patients receiving thyroxine replacement

This study was undertaken to compare the sensitivity of the thyrotrophs to that of other tissues to T4 treatment in hypothyroid patients. To do so, we measured serum total and free thyroid hormones and TSH, in addition to several serum markers of peripheral tissue response to thyroid status, in 21 hypothyroid patients treated with 50-micrograms increments of T4 to a maximum of 200 micrograms daily (group I) and in 104 clinically euthyroid patients receiving a long term constant replacement dose (group II). In group I patients, dose-dependent increases (P less than 0.05) in serum glutathione S-transferase, sex hormone-binding globulin, and angiotensin-converting enzyme occurred, whereas serum T4-binding globulin, creatine kinase, and creatinine levels decreased (P less than 0.05). In both patient groups, abnormally high levels of glutathione S-transferase, sex hormone-binding globulin, angiotensin-converting enzyme, alanine aminotransferase, and gamma-glutamyl transferase were found in some patients during treatment. One or more of these biochemical abnormalities suggestive of hyperthyroidism occurred in 15 (71%) group I patients and 27 (26%) group II patients. These were associated with an undetectable serum TSH (less than 0.1 microU/ml) and raised free T4 concentrations in 13, and raised free T3, T4, and T3 concentrations in only 8, 6, and 1 group I patients, respectively. In group II patients, they were more closely associated with an undetectable TSH (67%) or raised free T4 (85%) level than with raised concentrations of free T3 (33%), T4 (26%), or T3 (0%). The use of high sensitivity TSH assays will permit more accurate adjustment of T4 replacement and minimize abnormalities in peripheral tissue biochemistry indicative of overtreatment.

Value and limitations of a highly sensitive immunoradiometric assay for thyrotropin in the study of thyrotroph function

Using a highly sensitive and specific immunoradiometric assay for thyrotropin, we studied thyrotroph function in 232 new patients referred to a thyroid clinic and in 13 patients after treatment for hyperthyroidism. Significant thyrotroph responsiveness to thyroliberin (thyrotropin-releasing hormone, TRH) was found in all patients with values for basal thyrotropin greater than 0.1 milli-int unit/L. In no overtly hyperthyroid patient was any increment in thyrotropin recorded at 20 min after thyroliberin administration. In seven patients, four subclinically hyperthyroid and three who had received treatment, increments in thyrotropin from undetectable basal values were recorded, consistent with incomplete thyrotroph suppression. By use of assays with even higher sensitivity, one may be able to distinguish these patients from overtly hyperthyroid patients.

Value and limitations of a highly sensitive immunoradiometric assay for thyrotropin in the study of thyrotroph function

Using a highly sensitive and specific immunoradiometric assay for thyrotropin, we studied thyrotroph function in 232 new patients referred to a thyroid clinic and in 13 patients after treatment for hyperthyroidism. Significant thyrotroph responsiveness to thyroliberin (thyrotropin-releasing hormone, TRH) was found in all patients with values for basal thyrotropin greater than 0.1 milli-int unit/L. In no overtly hyperthyroid patient was any increment in thyrotropin recorded at 20 min after thyroliberin administration. In seven patients, four subclinically hyperthyroid and three who had received treatment, increments in thyrotropin from undetectable basal values were recorded, consistent with incomplete thyrotroph suppression. By use of assays with even higher sensitivity, one may be able to distinguish these patients from overtly hyperthyroid patients.

Comparison of radioimmunoassay and immunoradiometric assay for serum prostatic acid phosphatase

We have compared the laboratory performance of immunoradiometric (IRMA) and radioimmunoassay (RIA) methods developed in this laboratory for measurement of serum prostatic acid phosphatase (PAP). The IRMA utilizes a radiolabelled mouse monoclonal anti-PAP and a solid phased rabbit polyclonal anti-PAP. The same rabbit antibody is used in the RIA. The IRMA shows excellent precision over a much wider working range (0.25-1000 micrograms/l) than the RIA (0.73-14.0 micrograms/l), and can be completed in 5 h, while the RIA requires 3 days. Levels in healthy males and in patients with benign prostatic hypertrophy are similar in both assays, upper limits of normal being 1.8 micrograms/l (IRMA) and 4.7 micrograms/l (RIA). The two assay methods correlate very well (r = 0.97) when PAP is measured in serum from prostatic cancer patients, although IRMA results are generally lower than those obtained by RIA. About 20% of patients with non-metastatic prostatic carcinoma had elevated serum PAP, whereas about 80% of those with metastatic disease had raised levels. The diagnostic efficiencies of the RIA and IRMA appeared similar. The value of the IRMA in follow-up and staging remains to be determined.

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.

An improved approach to thyroid function testing in patients with non-thyroidal illness

We have compared the results of serum thyrotrophin (TSH) measurements using a sensitive immunoradiometric assay (IRMA) with those of conventional thyroid function tests in 299 hospital inpatients with a range of non-thyroidal illnesses. Levels of total thyroxine (T4), free T4, total tri-iodothyronine (T3) and free T3 in the hypothyroid range were recorded in 8%, 15%, 19% and 49% of patients, respectively, whereas TSH (IRMA) was abnormally low in 1%. Furthermore, basal TSH (IRMA) accurately predicted the result of the thyrotrophin-releasing hormone test in 72 of the 74 patients in whom this test was performed and, unlike thyroid hormone measurement, identified patients with subclinical thyroid disease. It would appear that a single basal TSH (IRMA) measurement is the most appropriate screening test for thyroid dysfunction in patients with concomitant acute or chronic illness.