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E J Sampson

Publications and source records attributed to E J Sampson.

16 recordsLinked to original sources
PubMed1991

Factors influencing the accuracy of the national reference system total cholesterol reference method.

Previous comparisons between the Reference and Definitive Methods for measuring serum cholesterol have demonstrated a small but persistent positive bias in the Reference Method, averaging about +1.6%. Here we describe the results of further investigations designed to better characterize the nature of this bias. Analysis of a well-characterized model serum sample (SRM 909) suggests that more than half of the difference in cholesterol values determined by the two methods is the result of small contributions from cholesterol precursor sterols and phytosterols, which are also measured for the Reference Method. An additional significant contribution may be from cholesterol oxidation products, particularly 7-hydroxycholesterol isomers, which are active in the Liebermann-Burchard reaction. The 7-hydroxycholesterol in SRM 909, most of which appeared to be already present in the serum rather than formed during saponification, may account for as much as 20% of the observed difference between the methods. Contributions from other possible sources, including impurities in the cholesterol standard and incomplete saponification of cholesteryl esters, are very small. Because the observed bias is both quite small and consistent among samples, the cholesterol Reference Method continues to meet all of the requirements generally expected for a dependable and effective Reference Method.

Carbon Isotopes↗
PubMed1979

Relative stabilities of purified human mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase in lyophilized materials.

Eight different pools of purified human mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase were prepared, to examine the effects of the following matrix variables: the matrix support material (bovine serum albumin and polyvinylpyrrolidone), endogenous pyridoxal concentration, and azide as an antimicrobial preservation. Storage temperatures of 25 and 37 degrees C were used as a rapid and convenient means of accelerating the degradation process. Activity of the enzyme was measured with and without pyridoxal in the reaction solution. We found that the mitochondrial isoenzyme was consistently more labile than the cytoplasmic isoenzyme under identical storage conditions. Both isoenzymes were more stable in matrixes containing bovine serum albumin than in those containing polyvinylpyrrolidone. No apparent difference in the stability of either isoenzyme was observed at matrix pyridoxal concentrations of 15 micromol/L and 150 micromol/L. Only the mitochondrial isoenzyme in matrixes containing bovine serum albumin and 15 micromol of pyridoxal per liter had increased activity (about 9%) when pyridoxal was added to the enzymatic reagent. The amount of activity in reconstituted specimens did not apparently change after 72 h at 4 degrees C.

Aspartate Aminotransferases↗
PubMed1979

Column chromatography and immunoassay compared for measuring the isoenzymes of aspartate aminotransferase in serum.

We compare a column-chromatographic method and a homogeneous immunoassay method for separately measuring the mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase. Analytical recovery for the two methods averaged 102% (SD, 2%) and 103% (SD, 4%), respectively, for 11 pools prepared by adding the purified isoenzymes to serum and 102% (SD 8.9%) and 89% (SD, 8.1%) for 26 unaltered specimens of human serum. In comparing the results of the immunoassay method (y) to the chromatographic method (x), our measurements agreed closely for the mitochondrial (y = 0.947 X + 7, r = 0.9991, standard error of estimate = 2.9 U/L) and cytoplasmic (y = 0.92x-6, r = 0.9995, standard error of estimate = 2.1 U/L) isoenzymes in pools prepared from the purified isoenzymes. Similar measurements of the 26 human serum specimens yielded the following results for least-squares evaluation; cytoplasmic isoenzyme y = 1.03x-11, r = 0.994, and standard error of estimate = 6.0 U/L; mitochondrial isoenzyme y = 0.75x+0, r = 0.927, and standard error of estimate = 3.9 U/L.

Aspartate Aminotransferases↗
PubMed1979

Chemical inhibition used in a kinetic urease/glutamate dehydrogenase method for urea in serum.

We describe a fixed-time-interval, kinetic inhibition method, with use of a competitive inhibitor (l) of the urease/glutamate dehydrogenase reaction to increase the "apparent" Michaelis constant by a factor of (1 + [l]lKl). This allows greater flexibility in selecting an appropriate sample dilution for kinetic determinations of urea in serum (i.e., [S]lKm ratio). Nine compounds were screened as potential inhibitors for this study. Adding 5 mmol of hydroxyurea per liter increases the "apparent" Michaelis constant for the coupled enzyme reaction by 10-fold. We used a sample dilution of 21-fold vs. dilutions of 141- to 350-fold for previously reported kinetic methods. Mean analytical recovery with this method was 100.2%. Reaction rate vs. urea concentration was linear, and complete recovery extended to 30 mmol of urea per liter. Of 22 potential interferents, only fluoride (250 mmol/L) and bilirubin (1 mmol/L, or 580 mg/L) caused greater than 5% interference. We discuss precision and effects of specimen dilution, and compare results for 100 specimens with those by a manual Berthelot-indophenol method, a manual diacetyl monoxime method, and a diacetyl monoxime method adapted to continuous-flow analysis.

Autoanalysis↗
PubMed1978

Column-chromatographic separation of isoenzymes of aspartate aminotransferase.

We describe a column-chromatographic method for separating the mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase in human serum. Bed height of the ion exchanger, pH, and salt concentrations in the eluting buffers are shown to be variables affecting the separation of the isoenzymes. Under the optimized conditions selected for this study, a 30% increase in volume was observed in one fraction, associated with changing the salt concentration of the eluting buffer and attributed to a contraction of the DEAE-Sephadex A-50. Elution profiles (enzyme activity vs. fraction number) were examined with highly purified mitochondrial and cytoplasmic isoenzymes of human origin in bovine serum albumin and human serum. Recovery of the enzyme in the eluted fractions averaged 102% (SD, 2.0%) for specimens prepared from the purified isoenzymes and 104% (SD, 10.7%) for 38 human serum specimens. The separation technique showed linearity to catalytic concentrations in excess of 200 U/liter (reaction temperature 30 degrees C) for each isoenzyme. Additional information is presented regarding among-day precision and the effect of specimen dilution.

Aspartate Aminotransferases↗
PubMed1978

An interlaboratory study of measurement of aspartate aminotransferase activity with use of purified enzyme materials.

The Center for Disease Control (CDC), the New York State Department of Health (NYSDH), the College of American Pathologists, and 23 manufacturers of diagnostic products participated in an interlaboratory study of aspartate aminotransferase (EC 2.6.1.1) methodologies. Six different lyophilized materials were prepared and characterized and then distributed to 293 laboratories for aspartate aminotransferase measurements. The specimens included one human serum; four catalytic concentrations of the cytoplasmic isoenzyme, two purified from human erythrocytes, and two from porcine heart; and one matrix bovine serum albumin (30 g/liter) blank. The purified isoenzymes were prepared in the matrix. We present data on Michaelis parameters (Km and Vmax), Arrhenius plots, activation with pyridoxal 5-phosphate, vial-to-vial variability, and stability on reconstitution. The 281 responses showed that most of the laboratories used NADH-detection methods (91.1%), monitored at 340 nm (79.4%), and reported results in U/liter (89.4%). The percentage of laboratories reporting use of reaction temperatures of 30 and 37 degrees C was evenly divided, i.e., 42.7 and 42%, respectively. Analytical values reported by participating laboratories were categorized by reporting temperature, instrument, and method. Results were most consistent for a selected group of laboratories that supplemented optimized reaction solutions with pyridoxal 5-phosphate.

Aspartate Aminotransferases↗
PubMed1977

Temperature dependence of the absorbance of alkaline solutions of 4-nitrophenyl phosphate--a potential source of error in the measurement of alkaline phosphatase activity.

The absorbance of an alkaline solution of 4-nitrophenyl phosphate is a function of temperature. Quantitative evaluation of this phenomenon indicates that it (a) depends on the concentration of the compound and is independent of source, buffer concentration, and pH above 9.0; (b) is reversible; (c) is not a result of alkaline hydrolysis or 4-nitrophenol contamination; and (d) correlates with a temperature-induced shift of its absorbance spectrum. The phenomenon may represent a potential analytical problem in methods for alkaline phosphatase in which this compound is the substrate. If thermal equilibrium is not reached and maintained during an alkaline phosphatase assay, the thermochromic response will be included in the measured rate. The magnitude of this error depends on the thermal response and control characteristics of each particular instrument and the reaction conditions under which such an analysis is performed.

Alkaline Phosphatase↗
PubMed1976

Comparison of serum gastrin radioimmunoassay kits.

1. Two commercially available kit procedures for gastrin measurement were investigated. 2. While the precision of both kits appeared comparable, discrepancies were observed in both accuracy and parallel studies and in the comparison of kit standards and patients' samples.

Evaluation Studies as Topic↗
PubMed1976

A comparative study of micro-ammonia determinations in plasma using two different methods.

Two commercially available kits for determining blood ammonia were compared, an enzymatic method requiring a sample volume of 100mul and a nonenzymatic method requiring 1 ml of sample. Calibration curves for both kits were linear to 270 mumol/l, however correlation studies on plasma samples revealed a lack of agreement between methods (r equal to 0.825, Y equal to 0.76X +51). Improved correlation occurs when protein interference is eliminated from the enzymatic procedure. Finally, the nonenzymatic method is modified to accommodate 100 mul of sample and compared to the original method.

Ammonia↗
PubMed1976

Comparison of two radioimmunoassay kits for aldosterone determination.

Two commercially available radioimmunoassay kits for aldosterone determination not requiring preliminary chromatographic purification were examined. Aldosterone standard curve solutions prepared from the CIS kit, Nuclear International Corp., (x-axis) and Diagnostic Products kit (y-axis) were assayed with both kits and the results yielded a regression equation of y = 0.834x + 0.08 nmol/liter. Analytical recovery experiments with aldosterone added to urine and serum showed 120% and 101% recovery with the CIS kit, respectively, and 92% and 92% recovery with the Diagnostic Products kit, respectively. Both kits demonstrated good parallelism with urine and serum. Antibody specificity was tested with six structurally related steroids and each kit showed virtually no cross-reactivity at clinically normal serum concentrations. Serum aldosterone values were compared before (y-axis) and after (x-axis) column chromatography on Sephadex LH-20, with the following regression equations: y = 1.070x + 0.092 nmol/liter for the CIS kit and y = 1.023x + 0.093 nmol/liter for the Diagnostic Products kit. Regression equations comparing patient samples between kits, CIS (x-axis) and Diagnostic Products (y-axis), were: y = 0.832x + 0.007 mumol/24 h with urine and y = 0.850x + 0.097 nmol/liter with serum.

Aldosterone↗
PubMed1976

Comparison of results for 13 clinical laboratory determinations with three automated analytical systems.

We evaluated the Abbott Bichromatic Analyzer-100 (ABA-100) for use in the routine clinical chemistry laboratory by examining 13 different determinations that can be performed on the instrument. Results with the Du Pont "aca" and Technicon continuous-flow systems were compared to the ABA-100 in terms of upper limits of linearity, inter-run coefficient of variation, and results for samples from patients. The upper limits of linearity for the methods on the ABA-100 exceeded all of those for the continuous-flow systems, except for urea nitrogen. Precision of the ABA-100 was as good as or better than that of the aca for all determinations, except for glucose in a normal control serum and creatine kinase and creatinine in an above-normal control serum.

Alanine Transaminase↗
PubMed1975

Faster enzymatic procedure for serum triglycerides.

We describe a single-reagent, enzymatic procedure for triglycerides in serum, which may be performed in 5 min per sample with use of an Abbott ABA-100 analyzer system. This procedure is compared to the semi-automated enzymatic procedure with the ABA-100, which requires 30 min per sample.

Autoanalysis↗