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Biomedical subjects

T A Walmsley

Publications and source records attributed to T A Walmsley.

At least 19 recordsLinked to original sources
PubMed1992

Increase in selenium status of Christchurch adults associated with deregulation of the wheat market.

AIMS: to determine whether there have been changes in the plasma selenium status of Christchurch adults between 1981 and 1992, and likely causes of any such changes. METHOD: selenium analyses were performed on plasma samples collected during the period. Changes in agricultural practices and importation policies were also examined. RESULTS: mean plasma selenium levels ranged between 46 and 54 micrograms/L (0.59-0.69 mumol/L) until 1987, after which there was a dramatic and sustained increase to between 66 and 70 micrograms/L (0.84-0.88 mumol/L) for 1988-91, with a 1992 mean of 80 micrograms/L (1.01 mumol/L). This increase closely follows the deregulation of the New Zealand wheat market and greater South Island consumption of wheat imported from Australia and the United States. Whereas flour was made from South Island wheat prior to 1988 and contained about 15 micrograms/kg selenium, flour manufactured by Christchurch mills in 1991 contained between 80 and 140 micrograms/kg. CONCLUSIONS: these results imply that as a result of current government policy, the population of Christchurch no longer has particularly low selenium levels. It follows that if there is an association between low selenium and any form of ill health, a declining incidence or severity in this population might be expected.

Adult↗
PubMed1992

Industrial blood lead levels in the South Island during 1988 and 1989: trends and follow up patterns.

AIMS: to assess trends in industrial lead exposure and the monitoring programmes in the South Island of New Zealand. METHODS: during the period 1 January 1988 to 31 December 1989, industrial lead exposure was analysed in 1425 workers in at risk occupations and the efficiency of retesting programmes was determined. RESULTS: forty-four percent of these workers had red cell lead levels above 1.9 mumol/L, the top of the reference range for an unexposed population, and 71 individuals had levels exceeding the recommended action limits (males greater than 5.0 mumol/L, and females greater than 3.8 mumol/L). Although most occupational groups showed a small decline in mean red cell lead levels, the pattern of exposure was similar to previous reports. On average, only 43% of exposed workers were retested within the recommended period and 32% of these workers were not retested within 2 years of having a raised blood lead level. CONCLUSIONS: retesting was inefficient but was most reliable when industrial health nurses were employed for monitoring. Not all lead poisoning comes from the traditional lead based industries and significant decreases were found in workers whose primary exposure is to lead from petrol.

Aftercare↗
PubMed1992

Apolipoprotein B-32: a new truncated mutant of human apolipoprotein B capable of forming particles in the low density lipoprotein range.

We have identified a new species of apolipoprotein (apo) B in an individual with heterozygous hypobetalipoproteinemia. The new apo B (apo B-32) is the result of a single point mutation (1450 Gln----Stop) in the apo B gene that prevents full length translation. Apo B-32 is predicted to contain the 1449 amino-terminal amino acids of apo B-100 and is associated with a markedly decreased low density lipoprotein (LDL) cholesterol level. The density distribution of apo B-32 in the plasma lipoproteins makes it unique amongst other truncated apo B species. Normally, apo B-100 is found in both very low density lipoprotein (VLDL) and LDL particles. However, the majority of the apo B-32 protein was found in the high density lipoprotein (HDL) and lipoprotein-deplete (d greater than 1.21 g/ml) fractions, suggesting that it was mainly assembled into abnormally dense lipoprotein particles. A small amount of apo B-32 was also found in the LDL, making it the shortest known apo B variant capable of forming particles in this density range. Apo B-32 was undetected in VLDL. The apo B-32 mutation further defines the minimum length of the apo B protein that is required for the assembly of LDL.

Aged↗
PubMed1992

A competitive ELISA for lipoprotein(a).

A competitive ELISA for lipoprotein(a) (Lp(a)) is described. The method uses a commercially available polyclonal anti-Lp(a) antibody and an IgG biotinstreptavidin-horseradish peroxidase detection system. The method is simple and robust with an assay sensitivity of 0.7 ng/well (1.4 micrograms/l). The antibody cross-reactivity was 0.14% against LDL and 0.70% against plasminogen. The coefficients of variation obtained with control sera of 266 and 552 mg/l were: 5.0% and 4.6% (n = 6), respectively for the intraassay; and 10.8% and 9.5% (n = 16), respectively for the interassay. The method showed an excellent correlation with a commercial immunoradiometric assay (IRMA), y (ELISA) = 0.94x (IRMA) - 8, (r = 0.98). A recovery study in which a 200 mg/L standard and four plasma samples were diluted with different proportions of a low plasma sample, gave linear relationships and also confirmed the specificity of the antibody.

Binding, Competitive↗
PubMed1992

Colorimetric measurement of iron in plasma samples anticoagulated with EDTA.

AIMS: To determine if the iron in EDTA anticoagulated plasma samples can be measured by colorimetric assays using Ferrozine. METHODS: Paired samples of serum and EDTA plasma were obtained from 24 patients and analysed by three commercial iron methods. The EDTA plasmas were also analysed using methods modified by the addition of zinc sulphate or with different concentrations of Ferrozine. The iron contamination of EDTA sample tubes was measured by atomic absorption spectroscopy. RESULTS: Two commercial colorimetric iron methods gave results of zero for EDTA plasma samples. A third commercial reagent gave plasma results that were about 30% lower than their corresponding serum samples. Addition of 7 mmol/l zinc sulphate to this reagent system and extending the sample preincubation time to 300 seconds yielded comparable results from paired serum and EDTA plasma samples. Linear regression analysis gave a slope of 0.97 with an intercept of 0.60 mumol/l and R2 = 0.9943. Measurements by atomic absorption spectroscopy showed that this positive intercept was due to contamination of the blood collection tubes with about 90 ng of iron. CONCLUSIONS: Modification of commercial colorimetric iron methods permits the biochemical assessment of iron status and a full blood count from a single EDTA anticoagulated blood sample.

Anticoagulants↗
PubMed1991

Hyperlipidemia in stable renal transplant recipients.

Hyperlipidemia is a major risk factor for atherosclerosis and probably contributes to the increased cardiovascular mortality following renal transplantation. We studied the lipid profiles of 62 adults (29 males) with stable renal function (mean plasma creatinine 0.14 mmol/l, SD 0.07), 7 months to 21 years after renal transplantation. Fifteen patients (24%) were above the age- and sex-adjusted 95th percentile for total triglyceride and 10 (16%) for total cholesterol concentrations when compared with a local reference population. The most common lipoprotein abnormalities were type IIa (19%) and type IIb (13%). Multiple regression analysis demonstrated that the use of diuretics and angiotensin-converting enzyme inhibitors were significant factors determining plasma triglyceride concentrations. There were significant bivariate associations between plasma triglyceride concentration and duration since transplantation, plasma creatinine concentration and the use of ciclosporin and diuretics. Duration since transplantation and ciclosporin use were significant factors determining lower plasma cholesterol concentrations. The use of ciclosporin and diuretics was associated with a significantly higher apolipoprotein (apo) B concentration. The cholesterol/HDL cholesterol risk ratio correlated poorly with the apo B/apo A-1 ratio. The value of these ratios as predictors of coronary artery disease need to be established in renal transplant recipients.

Adult↗
PubMed1991

Effect of plasma triglyceride concentrations on the accuracy of immunoturbidimetric assays of apolipoprotein B.

We have studied the influence of triglyceride-rich particles on the analytical bias of apolipoprotein B measurements by various immunoturbidimetric methods. Three commercially available methods grossly overestimate apolipoprotein B in samples with even moderately above-normal triglyceride concentrations. This effect is due to the increased relative reactivity of very-low-density lipoproteins in these reagent systems, and can be eliminated by including Tween 20 (2 g/L) in the reagent buffer. We have developed, and describe, an automated immunoturbidimetric method that allows the accurate determination of apolipoprotein B in the plasma of patients with hypertriglyceridemia.

Apolipoproteins B↗
PubMed1987

Effect of daylight on the reaction of thiols with Ellman's reagent, 5,5'-dithiobis(2-nitrobenzoic acid).

The reaction of 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB, Ellman's reagent) with thiols is sensitive to daylight, in particular to ultraviolet radiation at wavelengths around 325 nm. Exposure to light at the absorbance maximum of the yellow product (the thionitrobenzoate ion) at 410 nm had no effect on the reaction. The light-sensitive species is apparently the DTNB, because a spectral-irradiation experiment showed that the wavelength of light that produced the maximum rate of absorbance change coincided with the peak absorbance of DTNB, and it was well separated from the thionitrobenzoate absorbance peak. Ascorbate is ineffective as a stabilizer and can produce an apparent increase in the rate of DTNB destruction. In a practical example we found the light interference to be severe when hydrolysis of propionylthiocholine by plasma cholinesterase (EC 3.1.1.8) was measured after a 20-min incubation. The apparent cholinesterase activity in clear glass or plastic tubes exposed to diffuse daylight could be decreased to 25% of the value obtained for samples in light-excluded tubes. We recommend the reaction be carried out in artificial room light, with total elimination of daylight, because window glass does not sufficiently attenuate 325-nm wavelength irradiation.

Cholinesterases↗
PubMed1984

Optimal conditions for 4-hydroxybenzoyl- and 2-furoylhydrazine as reagents for the determination of carbohydrates, including ketosamines.

4- Hydroxybenzoylhydrazine ( PAHBAH ) reacts with glucose in hot aqueous solution when alkali exceeds aroylhydrazine concentration. The related 2- furoylhydrazine ( FAH ) reacts at lower alkali concentrations, making this an attractive alternative carbohydrate reagent since it is (unlike PAHBAH ) freely water soluble. FAH reacts with monosaccharides more slowly than does PAHBAH , giving about half the color. Its specificity and behavior with a bismuth catalyst parallel those of PAHBAH . Solutions which contain 0.05 mol/liter PAHBAH with 1.5 mmol/liter bismuth III (as tartrate complex) and 0.5 mol/liter sodium hydroxide, or 0.01 mol/liter FAH with 1.5 mmol/liter bismuth III and 0.1 mol/liter sodium hydroxide are sensitive reagents for quantitative analysis, giving stable colors with many carbohydrates within 10 min at 75 degrees C. Ketosamines react more rapidly than glucose at lower temperatures and undergo similar reactions in less alkaline solutions. At pH less than 8, the reaction is specific for these 1- aminohexoses , and FAH can be used as a reagent for their assay.

Autoanalysis↗
PubMed1983

Microsampling on the Technicon SMAC system.

The sample volume needed for a Technicon SMAC continuous-flow analyzer has been reduced for routine operation. Two options are available: 141 microL for a 17-test profile, or 224 microL, which allows the direct-sampling assays for creatinine and iron to be included. The sample decrease is achieved by the sequential dialysis of creatinine and iron, an increased sample dilution from sixfold to ninefold, the strict minimization of diluted sample stream wastage, and development of more sensitive methods for glucose and alkaline phosphatase to allow greater use of the diluted sample stream. A glycine-containing diluent increases the sensitivity of the iron method by 25% and prevents the protein precipitation that plagues the continuous-flow analysis for iron in plasma. No deterioration in performance of the analyzer has been detected during nine months of routine operation at the reduced sample size. Added advantages are the decreased consumption of calibration materials and an increased ability to do repeat tests.

Alkaline Phosphatase↗
PubMed1982

Measurement of magnesium by continuous-flow colorimetry.

We describe the application to the Technicon SMAC system of a micellar-improved calmagite method for the measurement of magnesium. In this continuous-flow method a dialyzer is not needed, because protein interference is negligible. Sample interaction was estimated to be 3%. The increased sensitivity of the method allows for a small sample volume (37 microL/min). Results obtained agreed well with those by an atomic absorption procedure (x): SMAC magnesium - 0.971 x + 0.030 mmol/L (n = 58). The estimated total error for the SMAC procedure was less than 50 mumol/L at two analyte concentrations: 0.50 and 1.50 mmol/L. The inclusion of magnesium estimation on SMAC should extend the screening function of this analyzer.

Colorimetry↗
PubMed1981

Analytical errors in clinical laboratories as assessed by an interlaboratory survey.

Combined errors ar the commonest systematic errors in laboratory results and occur with most tests studied. In these errors, results are reduced (or, less commonly, increased) by a factor, and this effect is compensated by the addition (or subtraction) of a constant amount. The effect is that results are in error in opposite direction at high and low levels. Inconsistency is predominant and is due mainly to imprecision, although for some tests (iron, cholesterol, calcium, and triglycerides among those studied) other factors such as non-specificity are significant. An interlaboratory survey based upon external method assessment using linear regression analysis provided objective information about analytical error in laboratories which is not usually obtained, while at the same time meeting the usual functions of surveys in the quality audit of performance.

Data Collection↗
PubMed1979

Effects of sample-diluent interactions on surface tension and pressures in continuous flow manifolds.

When a plasma sample is aspirated into a continuous flow analyser the internal pressure of the manifold increases. The pressure change is the result of insufficient detergent present to bind all the protein in the sample, and is a potential source of inaccuracy and imprecision in the assay. It is recommended that Brij 35 be used at a concentration 10 times above the binding capacity of the albumin in the sample, to minimise changes in pressure between samples.

Autoanalysis↗