Evaluation of the Beckman "System TR enzyme Analyzer".
(57/1318)
We evaluated 16 claims made by Beckman Instruments, Inc. for its Enzyme Analyzer (System TR), under a rigid written protocol for the Product Evaluation Subcommittee of the Standards Committee of the College of American Pathologists. We found the following to be within the company's specifications: (a) accuracy and precision of the temperature control; (b) accuracy and precision of the sample and reagent pipets; (c) instrument precision, both within-run and between-day; (d) carry-over from a sample with activity greater than 1000 U/liter; (e) instrument-to-instrument variation; (f) analytical linearity; (g) analysis time; (h) correlation of the instrument-printed answer with the activity calculated manually from a strip-chart recorder; (i) precision of the instrument's built-in electronic "standard"; (j) effectiveness of the over-range indicators; and (k) correlation between results of these enzyme assay methods and those for kinetic methods used in our laboratory. The instrument performed well. (+info)
New Colorimetric reaction for end-point, continuous-flow, and kinetic measurement of urea.
(58/1318)
A reaction of urea, o-phthalaldehyde and N-(1-naphthyl)ethylenediamine is described for measurement of urea by manual, continuous-flow, and kinetic methods. The continuous-flow system requires 25 mu-l of sample; 40 samples can be analyzed per hour. The kinetic method requires no enzymes, has no lag phase, and has good sensitivity. A major advantage of the reaction is that it occurs at a temperature of 37 degrees C or lower. The results obtained by all three methods agree well with those for a continuous-flow procedure in which diacetyl is a reagent. (+info)
Interlaboratory proficiency, intermethod comparison, and calibrator suitability in assay of serum aspartate aminotransferase activity.
(59/1318)
Sources of variation in assays of aspartate aminotransferase (EC 2.6.1.1) activity were examined in an interlaboratory survey and through an examination of materials used as calibration materials in these assays. Four highly stable lyophilized specimens containing human cytoplasmic enzyme, with activities of 0, 22, 46, and 96 U/liter at 30 degrees C and optimal substrate concentrations, were assayed by 319 laboratories. Mean values obtained on these specimens by laboratories using 2,4-dinitrophenylhydrazine kits varied among manufacturers and deviated from values expected from this procedure. The average coefficient of variation (CV) with these kits was greater than 20%. Automated continuous-flow procedures with use of diazonium salt showed the best precision (av CV, less than 10%). However, the automated continuous-flow malate dehydrogenase/NADH coupled method produced an average CV greater than 20%. Results from each of the automated methods were related to a reference malate dehydrogenase/NADH coupled continuous kinetic assay method by temperature relationships alone. Mean values from manual diazonium salt procedures were 1.7-fold greater than similar reference values (av CV was 18%). The higher results were attributed to the use of poorly-defined units and to an artifact caused by chromophore stabilizers in this procedure when aqueous samples are used. The average CV in continuous kinetic methods varied among kit manufacturers, ranging from 6 to 28% for the specimen of highest activity. Variations in results were much larger at 366 nm than at 340 nm than at 340ity. Variations in results were much larger at 366 nm than at 340 nm. Interassay relationships of these methods are presented. Concentrations of pyruvate in commercially available calibration materials differed between manufacturers, varied in stability, and deviated from the expected concentration. For some colorimetric assays the precision attained on reported absorbance values for the enzyme specimens was of the same order of magnitude as that for pyruvate standards. Other sources of error are revealed by the interlaboratory survey. The value of commercially available sources of enzyme activity as calibration or control materials was assessed by evaluating the following properties: activity at suboptimal concentrations of L-aspartate or 2-oxoglutarate, temperature effects, preincubation lability owing to aspartate and phosphate, pyridoxal phosphate saturation, contamination with glutamate dehydrogenase, and manufacturer's rated activity. These properties are compared to those of human cytoplasmic enzyme in a human serum matrix. (+info)
Rapid and portable methods of lactose tolerance test administration.
(60/1318)
Abbreviated, portable methods of lactose tolerance test administration were investigated. Results obtained with the Ames Reflectance Meter/Dextrostix system for blood glucose determination during lactose tolerance testing were compared with those obtained from a standard method, the AutoAnalyzer. Subjects who had maximum blood glucose rises below 20 mg/100 ml were considered to have a flat lactose tolerance curve and were designated lactose nondigesters. Results of the two methods were very similar for determination of maximum rise in blood sugar over fasting level, for obtaining values of individual blood sugar determinations, and for diagnosis of lactose nondigesters. The effect of omission of the final blood sample on tolerance test results was examined. It was found that maximum rises in blood glucose occurred before the final sample in 31 of 35 cases on the AutoAnalyzer and in 26 of 27 cases on the Reflectance Meter. In no case did omission of the final sample change the results of the lactose tolerance test. (+info)
Simultaneous multianalyte ELISA performed on a microarray platform.
(61/1318)
BACKGROUND: A logical progression of the widely used microtiter plate ELISA is toward a protein array format that allows simultaneous detection of multiple analytes at multiple array addresses within a single well. Here we describe the construction and use of such a multiplex ELISA to measure prostate-specific antigen (PSA), alpha1-antichymotrypsin-bound PSA (PSA-ACT), and interleukin-6 (IL-6). METHODS: We silanized glass plates and printed the appropriate capture antibodies to allow for the construction of "sandwich" ELISA quantification assays. We examined specificity of the assay for appropriate antigen, assembled calibration curves, and obtained PSA concentrations for 14 human serum samples. We compared the serum PSA concentrations derived through the use of our array with values obtained independently using a standard ELISA method. RESULTS: R2 values generated by our microarray for the PSA and PSA-ACT calibration curves were 0.989 and 0.979, respectively. Analyte concentrations used for the construction of these curves were 0.31-20 microg of protein/L of diluent. IL-6 calibration curve concentrations were 4.9-300 ng of IL-6/L of diluent. The R2 value for the IL-6 calibration curve was 0.983. The 14 human serum samples screened by this micro-ELISA technique for PSA concentrations generated a regression equation (linear) with a slope of 0.83 +/- 0.10 and intercept of 0.74 +/- 0.70 (R2 = 0.88). CONCLUSIONS: Multiplexed ELISA arrays are a feasible option for analyte quantification in complex biologic samples. (+info)
The presence of hemoglobin S and C Harlem in an individual in the United States.
(62/1318)
The first reported case of hemoglobin S and C Harlem in an individual is described. The patient, a 35-yr-old female, had numerous crises during adolescence and early adulthood, but these occurred more infrequently as she grew older. Chemical evidence is presented for the characterization of both variant hemoglobins. The clinical course of this individual with Hb S in combination with Hb C Harlem appears to be similar to that for persons with sickle cell anemia. (+info)
Applications of a Vidicon spectrometer to analytical problems in clinical chemistry.
(63/1318)
This report discusses characteristics of a custom-designed vidicon spectrometer and evaluates its applicability to several clinical analysis problems. Data show that the vidicon detector response is linear with intensity over about four orders of magnitude and that the uncertainty in absorbance measurements can approach 0.001 absorbance units in the range from 0 to 2 absorbance units. Applications include the enzymatic determination of glucose, the determination of lactate dehydrogenase, and determinations of barbital, chlordiazepoxide, and glutethimide. Capabilities of the instrument system for first-derivative spectroscopy are also discussed. The discussion included a critical evaluation of the potential advantages and limitations of the concept. (+info)
Improved measurement of erythrocyte volume distribution by aperture-counter signal analysis.
(64/1318)
In aperture counters, particles in fluid suspension flow through a small orifice or aperture, causing a change in the electrical resistance of the aperture. This change is sensed by an external electronic circuit and translated into a voltage pulse, the signal height of which is proportional to the volume of the particle in the aperture. These signal pulses are collated into a spectrum of pulse heights by a multichannel pulse-height analyzer. The channel number (voltage increment) spectrum is proportional to the volume distribution of the particles sensed. A problem is that pulse height not only depends on cell volume, but also on the orientation and shape of the particle sensed and the current density along the path taken by the particle through the aperture. Uneven current density exists, primarily at the aperture entrance and exit, close to the wall. Orientation and shape of particles are altered near the wall by the unbalanced shear forces there. Toward the center of the aperture, the shear forces act so as not to induce continuous change in the orientation of the particles sensed. Thus introduction into the pulse-height spectrum of pulses that do not show a good proportionality to volume is primarily caused by particles that are traveling near the aperture wall. Residence time in the aperture for a particle traveling near the wall will be longer than that for a particle traveling down the center of the aperture, because of the smaller fluid velocity near the wall. Duration of the signal pulse created by a particle traveling near the wall will be correspondingly greater. We discuss an electronic filter to remove from the pulse-height spectrum those pulses that appear to result from particles traveling near the wall and the effect of the filter on the measured signal height and hence the volume distribution of erythrocytes. Use of this technique to characterize erythrocytes by volume distribution is described. (+info)