Search PubMed⌕ Search

Biomedical subjects

W G John

Publications and source records attributed to W G John.

At least 19 recordsLinked to original sources
PubMed2004

Introduction of IFCC reference method for calibration of HbA: implications for clinical care.

Abstract HbA(1c) is recommended for monitoring glycaemic control and quantifying the risk of complications in patients with diabetes. National guidelines for treatment of patients with diabetes in UK specify that HbA(1c) measurements should be Diabetes Control and Complications Trial (DCCT)-aligned i.e. comparable to the DCCT and UK Prospective Diabetes Study (UKPDS). The IFCC reference method for HbA(1c) will be introduced in Europe in December 2003 for calibration of all laboratory and POCT (point of care testing) methods for HbA(1c) following the recent EC "In Vitro Diagnostic" (IVD) directive. This reference method involves measurement of HbA(1c) and HbA(0) by electron-spray ionisation-mass spectrometry or capillary electrophoresis with the reference range approximately 2% HbA(1c) lower than the corresponding range from the DCCT. However, this EC IVD directive will not change reporting of DCCT-aligned HbA(1c) in the UK. Professionals involved in the care of patients with diabetes in the UK met with Dr Sue Roberts in London in July 2003. It was decided that in the UK DCCT-aligned HbA(1c) will continue to be reported from December 2003 for patient care and that laboratories currently reporting non-aligned DCCT HbA(1c) should change to reporting DCCT-aligned results as soon as possible. It was considered important for diabetes care in the UK that the reporting of HbA(1c) should not fragment. The UK HbA(1c) Standardization Committee was set up to hold "a watching brief " on HbA(1c) especially with relation to reporting of HbA(1c) in other countries.

Biomarkers↗
PubMed2000

A reliable non-separation fluorescence quenching assay for total glycated serum protein: a simple alternative to nitroblue tetrazolium reduction.

A simple non-separation assay for the measurement of total glycated serum protein is described. It was found that the fluorescence intensity of a solution of a fluorescein-boronic acid derivative was quenched in proportion to the amount of serum added. This led to the development of an assay in which 10 microL of serum is added to 4 mL of a solution of the fluorescein-boronic acid derivative and the fluorescence intensity is measured after 15 min. The results, as measured by drop in fluorescence intensity, calibrated by a single standard, were compared with the results for nitroblue tetrazolium (NBT) reduction of fructosamine and showed good correlation (r=0.936, n=114). The intra-assay precision (seven samples each measured 10 times) was less than 2.1% (concentration range 190-660 micromol/L); inter-assay precision for seven samples in 10 assays was less than 2.5% (over the same concentration range). Dilution of serum that had a high concentration of total glycated protein showed the assay to be linear. Serum samples (with low, medium and high total glycated protein concentrations) showed less than 2.1% difference from base results with added glucose (up to 60 mmol/L), less than 9.7% difference with added bilirubin (up to 250 micromol/L) and less than 6.9% with added triglycerides (up to 50 mmol/L). Addition of haemoglobin (up to 0.9 g/dL) with high glycation (11.7% HbA1c) to plasma (298 micromol/L total glycated protein) showed less than 10% difference from the base result. Assays performed over a range of temperatures (12-34 degrees C) showed no significant differences in the results. The assay gives similar results to the currently used NTB method but with significantly less susceptibility to interferences. As such the method should be a useful aid in the management of diabetes.

Blood Proteins↗
PubMed1998

Alkaline phosphatase activity measurement in the UK by AMP-buffered methods: an appraisal of current practice.

Most UK clinical laboratories use alkaline phosphatase (ALP) methods similar to that proposed by the International Federation of Clinical Chemistry (IFCC), based on the use of 2-amino-2-methyl-1-propanol (AMP) buffer. We present evidence of significant differences in results produced by apparently similar commercial ALP methods using an AMP buffer. We compared Bayer DAX, Dade Dimension and Boehringer Mannheim Hitachi 717 methods. Boehringer and Dade results were higher than Bayer results (Bland and Altman analysis, log transformed data): Boehringer (+23.0%, limits of agreement 1.16-1.31 times Bayer); Dade (+21.9%, limits of agreement 1.13-1.32 times Bayer). Biases were predominantly due to differences in reagents rather than analyser characteristics. Compared to a reagent system prepared exactly as described by the IFCC, Bayer was sub-optimal and Dade and Boehringer methods produced results higher than the IFCC method. Reference ranges and results on patients' samples by the various methods showed large differences but no clinically significant difference was observed in external quality assessment schemes either between Bayer and Boehringer or against method means. Apparently similar methods produce different results in patients' sera: external quality assessment schemes are not useful in highlighting these differences.

Alkaline Phosphatase↗
PubMed1997

Adaptation of latex-enhanced assay for percent glycohemoglobin to a Dade Dimension analyzer.

At present no method for glycohemoglobin (%HbA1c) is automated on a main-line analyzer to allow joint measurement with other indicators of diabetic control such as glucose and cholesterol. We describe an adaptation of a latex-enhanced competitive immunoassay for quantifying %HbA1c to the Dade International Dimension analyzer. After a manual hemolysis step, HbA1c and total hemoglobin (Hb) are determined separately. The concentration of glycated beta-subunit is obtained from the immunoassay, whereas Hb is assessed colorimetrically from a derivatized form. Both reactions were fully optimized for accuracy, precision, and specificity on the Dimension; stabilities of reagents and calibration were established; and potential interferences were assessed. The analyzer gave reliable results over the required clinical range of 1-15% HbA1c. Within-run and total assay variation were within 5% of the target CV limits, as determined by ANOVA with three representative sample pools across 20 days. Close agreement with an established HPLC procedure and a commercially available enzyme immunoassay was observed for 140 samples from clinically defined patient groups. Additional samples from patients with hemoglobinopathies (n = 20) demonstrated a more complex relationship between methods. We conclude that adaptation of the method for use with the Dimension analyzer is a valid method for quantifying %HbA1c.

Autoanalysis↗
PubMed1997

Evaluation of the Menarini-Arkray HA 8140 hemoglobin A1c analyzer.

We describe a multinational evaluation of the Menarini-Arkray HA 8140 hemoglobin (Hb) A1c analyzer, which utilizes a high degree of automation, including bar code reading, cap piercing, and whole-blood sampling. With-in- and between-batch CVs were < 2%. Linearity was confirmed throughout the working range of the analyzer. Common Hb variants, including Hb S, Hb C, and Hb F, did not interfere with the Hb A1c separation, and the potentially interfering labile Schiff base was effectively removed during the chromatographic procedure. The HA 8140 analyzer displayed good correlation to the Bio-Rad Variant analyzer, Tinaquant immunoassay, affinity chromatography, and an optimized "in-house" HPLC Hb A1c method. The methods when compared by Altman and Bland plots showed bias (upper, lower 95% confidence limits) of: Variant minus HA 8140 = 0.99 (0.23, 1.74), Tinaquant minus HA 8140 = 0.14 (-0.71, 0.98); affinity minus HA 8140 (after log transformation) = 1.13 (0.90, 1.41), and "in house" HPLC minus HA 8140 (after log transformation) = 0.91 (0.82, 1.01).

Anticoagulants↗
PubMed1995

The effect of low dose recombinant human growth hormone replacement on regional fat distribution, insulin sensitivity, and cardiovascular risk factors in hypopituitary adults.

GH deficiency is associated with increased cardiovascular morbidity, which may be determined by alterations in vascular risk factors. We report the effect of partially treated hypopituitarism and subsequent GH replacement (mean dose, 0.2 IU/kg.week) on putative cardiovascular risk factors in 22 nondiabetic hypopituitary subjects in a 6-month, double blind, controlled study (active/placebo ratio, 11:11). All patients were subsequently treated with GH for a further 6 months. Total fat, percent body fat, and central fat were measured by dual energy x-ray absorptiometry. The hypopituitary patients had increased percent fat (P = 0.03) and central fat (P < 0.01) compared with body mass index-matched controls. Before GH treatment, fasting (total) and specific insulin positively correlated with body mass index (P = 0.02 and P < 0.001, respectively), waist/hip ratio (P = 0.05 and P = 0.01), and central fat (P = 0.03 and P = 0.003). Specific insulin and insulin sensitivity (IS), calculated by homeostatic model of assessment, were related to total fat (P < 0.001 and P = 0.02). GH treatment for 6 months led to a reduction in total fat (P < 0.02), percent fat (P = 0.002), central fat (P = 0.012), waist/hip ratio (P < 0.05), total cholesterol (P = 0.03), and apolipoprotein-B (P = 00001), as well as a decrease in the IS from 36.9% (range, 12-100%) to 25% (range, 2.5-55%; P = 0.0002). This was paralleled by a rise in fasting (total) and specific insulin (P = 0.016 and P = 0.002). The degree of correlation among indices of IS, body composition, and fat distribution increased after GH treatment. Fasting plasma glucose rose significantly, but was within the reference range. During 12 months of GH therapy, a significant increase in serum lipoprotein-(a) was observed (P < 0.05). Although GH has beneficial effects on central adiposity and lipid fractions, it is also associated with a decrease in IS; these effects may vary between individuals.

Adipose Tissue↗
PubMed1994

Laboratory evaluation of the DCA 2000 clinic HbA1c immunoassay analyser.

The DCA 2000 clinical analyser for the measurement of haemoglobin A1c was evaluated for analytical quality. The analyser, which utilises inhibition of latex agglutination immunoassay, demonstrated good within-batch (1.9-3.1% CV) and between-batch (2.2% CV) imprecision, and was not affected by haemoglobin concentration. The analyser was linear throughout the analytical range, and was found to correlate well with agar electroendosmosis (r = 0.93), affinity chromatography (r = 0.97), HPLC (r = 0.90) and EIA (r = 0.98). The analyser was found to give reliable analytical results, and with its ease of use, will provide the diabetologist with HbA1c results in the clinic; although an analysis time of 9 min will limit sample throughput.

Antibodies, Monoclonal↗
PubMed1993

Enzyme immunoassay--a new technique for estimating hemoglobin A1c.

We describe a method for estimating hemoglobin A1c (HbA1c) with a commercially available enzyme immunoassay system. The method is based on microtiter plate technology, utilizing an antibody raised to hemoglobin, the epitope being the Amadori product of glucose plus the first eight amino acids on the N-terminal end of the beta chain of hemoglobin. The enzyme immunoassay displays good within-batch (CV 2.3-2.4%) and between-batch (CV 2.6-5.0%) precision, and the results were not affected by different types of anticoagulant. The method was linear within the expected range of results and showed good correlation (r = 0.88-0.98) with established methods for estimating glycohemoglobin. Using this method, we obtained a reference interval of 2.8-4.9% (central 95%) for HbA1c in a nondiabetic population. The percentages of hemoglobin that were HbA1c in diabetics (6.86% +/- 2.51%) were significantly greater (P < 0.001) than in nondiabetics (3.46% +/- 0.52%).

Chromatography, High Pressure Liquid↗
PubMed1990

Glycated haemoglobin and fructosamine in non-diabetic subjects with chronic renal failure.

Measurements of glycated haemoglobin by electroendosmotic and chromatographic methods, fructosamine, and fructosamine:albumin ratio were made in 91 non-diabetic subjects with chronic renal failure managed conservatively (n = 25), by continuous ambulatory peritoneal dialysis (n = 22), by haemodialysis (n = 22), or by renal transplantation (n = 22). Results were compared with those in a control group of 43 non-diabetic subjects with normal renal function. Mean glycated haemoglobin measured by electroendosmosis was significantly greater in all groups with chronic renal failure except the transplant group. Mean glycated haemoglobin measured by affinity chromatography was not significantly different from controls in any of the groups with chronic renal failure. No difference in mean fructosamine concentration was detected in the transplant or conservatively managed groups compared to controls, but values were significantly lower in the CAPD group, and greater in the haemodialysis group predialysis. Post-haemodialysis samples showed a significant reduction in mean fructosamine concentration when compared with prehaemodialysis samples. Fructosamine:albumin ratios were elevated in all groups of patients with renal failure, with the exception of the transplant group. Of the four indices of glycaemic control considered in this study, only glycated haemoglobin measured by affinity chromatography appears to be unaffected by chronic renal failure.

Adolescent↗
PubMed1988

Glycated haemoglobin and glycated protein and glucose concentrations in necropsy blood samples.

Glycated haemoglobin and glycated protein (fructosamine) and blood glucose concentrations were measured in blood samples collected from 75 patients at necropsy. Estimation of blood glucose was a poor indicator of glycaemia before death. Measurement of glycated haemoglobin by affinity chromatography distinguished non-diabetic patients from diabetic patients. The distinction was not as clear cut when HbA1 was estimated using electroendosmosis. Seven patients, who at necropsy had no known history of diabetes, had glycated haemoglobin concentrations in the diabetic range. Two of these patients were found to be diabetic, and diabetes had been suspected at some time in another three patients. It is concluded that measurement of glycated haemoglobin or HbA1, in necropsy specimens is a valuable tool for assessing glycaemic control in known diabetic patients, and may be useful in diagnosing previously unsuspected diabetes.

Adult↗
PubMed1987

Glycated haemoglobin analyses--assessment of within- and between-laboratory performance in a large UK region.

The performance of glycated haemoglobin methods has been assessed in 20 laboratories. The methods used in these laboratories were affinity chromatography, electroendosmosis and ion-exchange chromatography. Assessment was based on the results returned by the participating laboratories on distributed specimens. Each method displayed acceptable precision and good linearity. Overall there were substantial differences in results reported by different laboratories, though within each method group these differences were less marked.

Chromatography, Affinity↗