Search PubMed⌕ Search

Biomedical subjects

J Seth

Publications and source records attributed to J Seth.

At least 19 recordsLinked to original sources
PubMed1992

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.

Adult↗
PubMed1992

Dietary modulators of lipid metabolism in the Indian diet-heart study (I.D.H.S.).

Of the 621 adults (25 to 65 years of age, 531 males) with either risk factors or with coronary heart disease (CHD) 310 subjects were given a cardiovasoprotective (CVP) diet (group A) and 311 subjects a normal diet (group B) in a randomized, single blind and controlled fashion. Risk factors and incidence of CHD were comparable between the two groups. The intervention group received a significantly higher percentage of calories in relation to complex carbohydrates, vegetable proteins, polyunsaturated fatty acids and high P:S ratio diet as compared to the control group. The control group received higher saturated fat and cholesterol. Compliance was assessed by dietary questionnaire during the follow-up. After 8 weeks of dietary trial, there was a significant decrease in mean serum total cholesterol (8.2 vs 2.1%), low density lipoprotein (LDL) cholesterol (9.8 vs. 2.7%) and triglyceride (11.2 vs 5.8%) in the intervention group compared to baseline levels and changes in control subjects. Body weight and physical activity at the entry to study and during the trial were similar in both groups. The decrease in mean HDL cholesterol were insignificant both in the intervention (4.3%) and control group (5.0%). There were no adverse effects of diet during the 8 weeks of trial. It is possible that a diet with 27.5% energy from total fat including 10.1% energy from monounsaturated fatty acids, P:S ratio 1.38, 120 mg dietary cholesterol, 26.0 g dietary fibre per 1000 kcal would modulate the lipid metabolism resulting in a significant reduction in serum total cholesterol, LDL cholesterol and triglyceride with no reduction in HDL cholesterol. This diet may be capable of reducing CHD incidence and mortality in the long term Indian diet-heart study (IDHS).

Adult↗
PubMed1991

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.

Adult↗
PubMed1991

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.

Antibodies, Monoclonal↗
PubMed1991

External quality assessment of immunoassays of peptide hormones and tumour markers: principles and practice.

External quality assessment schemes (EQAS) have traditionally emphasised the achievement of between-laboratory consensus. Although this is important, the application of EQAS to relatively new and evolving techniques such as immunoassay calls for a wider and more searching remit if the goals of accurate assays, properly used, are to be achieved. This article outlines the principles of EQAS for peptide hormones and tumour markers, emphasising key aspects such as validation of target values, dependency of results on sample type, and assessment of method characteristics such as vulnerability to interfering factors. The latter are considered to be important as they can affect patient care more seriously than modest degrees of imprecision or inaccuracy. EQAS play a unique role in providing objective data on assays performed in many laboratories under routine conditions and the data they provide can guide improvement in diagnostic reagents and laboratory practice.

Artifacts↗
PubMed1989

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.

Animals↗
PubMed1988

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].

Growth Substances↗
PubMed1988

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.

Growth Substances↗
PubMed1988

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.

Female↗
PubMed1987

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.

Adult↗
PubMed1987

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)

Adult↗