Biomedical subjects

R Chesler

Publications and source records attributed to R Chesler.

9 recordsLinked to original sources

PubMed1992

Rationale for using multiple regression analysis with complex interferences.

Non-specificities and interferences may become complex when they involve the analyte as well as other interfering substances. These non-specificities and interferences are known as analyte-dependent and multi-interferent interferences. Multiple regression analysis has proven valuable in analysing this type of interference, but the theoretical foundation for using multiple regression analysis to study the basic mechanisms of interference has not been explicitly demonstrated. Graph theory can depict and model the basic mechanisms of interferences and the possible interactions. The relationship between the analyte, the interferents, and the response of the instrument to these entities can be approximated by a polymial of order three, which includes partial derivatives and cross-terms. The partial derivatives relate to the different interactions found with the graph theory model. Further, the partial derivatives can be associated with the coefficients in the multiple regression analysis when the respective values of the three variables (analyte, interferent one, and interferent two) are multiplied by one another. One can decide to retain or discard the coefficient of a variable, based on the statistical significance of the coefficient. The respective interactions in the graphic model can then be assembled and the framework of the interference mechanism established.

Bilirubin↗

PubMed1990

Effect of serum lyophilization on the rate constants of enzymatic methods for measuring cholesterol.

We determined the equilibrium absorbances and rate constants for two enzymatic methods, aca (DuPont) and RA-1000 (Technicon), used in determining cholesterol in reconstituted lyophilized serum. The lyophilized materials included two serum pools, three control materials, a College of American Pathologists' survey material, and Standard Reference Material no. 909. We calibrated the reagents with aca standards for cholesterol (DuPont). The difference in the mean concentrations of cholesterol (aca - RA-1000) was -0.09 g/L overall and was not statistically significant by analysis of variance. The mean rate constant for all materials was 0.23 min-1 for the aca and 1.42 min-1 for the RA-1000, significantly different (P less than 0.001). Lyophilization causes lower results for the aca method than for the Ra-1000, because the reaction rate for the aca method is slower and has not reached equilibrium when the final absorbance reading is made.

Cholesterol↗

PubMed1989

Effect of lyophilization on results of five enzymatic methods for cholesterol.

We studied the effect of lyophilization of serum pools on the determination of cholesterol with the enzymatic methods used in five automated analyzers: SMAC (Technicon), the RA-1000 (Technicon), the aca (Du Pont), the TDx (Abbott), and the Ektachem 700P (Kodak). We prepared two serum pools: pool A (2.2 g/L) and pool B (1.9 g/L). We separated each pool into three groups for treatment by lyophilizing or freezing at -20 and -70 degrees C. We determined cholesterol by the above methods at regular intervals during the next 270 days. For all methods, the measured concentration of cholesterol was less for the lyophilized serum than for frozen (P less than 0.007 by the paired-sample t-test). After adjusting for the dilutional effects of reconstitution, the decrease in original value was 0.7% for the SMAC, 1.7% for the RA-1000, 5.7% for the Ektachem, 9.4% for the TDx, and 14.3% for the aca. Lyophilization of cholesterol standards or serum samples may hamper the effective standardization of enzymatic methods and may be a source of apparent inaccuracy (bias) among enzymatic methods.

Autoanalysis↗

PubMed1986

Automated determination of urinary creatinine without sample dilution: theory and practice.

The rate of the Jaffé reaction depends on the concentration of sodium hydroxide; the pseudo-first-order rate constant of the reaction, at 37 degrees C in 10 mmol/L picrate solution, is 0.004 mmol/L. We formulated an automated method to determine urinary creatinine directly without manual sample dilution. The conditions are as follows: 10 mmol/L picrate and 60 mmol/L sodium hydroxide (final concentrations); ratio of sample to final volume, 1:41; temperature, 37 degrees C; wavelengths of measurement, 500 or 510 nm; interval of measurement, 30 to 90 s; and mode of measurement, kinetic. Determinations of creatinine in patients' samples by the new method compared favorably with those obtained with the AutoAnalyzer and aca. The run-to-run CVs were 3.6% or less, and the method was accurate for concentrations of creatinine up to 3000 mg/L. We recommend this method as a good replacement for the AutoAnalyzer or aca methods.

Autoanalysis↗

PubMed1984

Exercise and the patient with Type I diabetes mellitus.

This article reviews the clinical features of heart disease in the diabetic in three categories: (1) coronary atherosclerosis (CAD), (2) autonomic neuropathy, and (3) cardiomyopathy. Particular attention is given to current methods of noninvasive assessment of cardiac function in juvenile diabetics.

Adolescent↗

PubMed1984

Comparison of the Du Pont aca and Dow methods for determination of high-density lipoprotein cholesterol.

We compared the Du Pont aca (phosphotungstate-enzymic cholesterol) and the Dow (dextran sulfate/Mg2+-enzymic cholesterol) methods for the determination of high-density lipoprotein cholesterol (HDLC) and total cholesterol in serum from 113 patients. The aca results for both total cholesterol and HDLC were significantly greater (p less than 0.0001) than the Dow results, the aca method overestimating the HDLC concentration (mean recovery 107.2% in serum samples with values assigned by the Centers for Disease Control). The precision of the aca method for HDLC was essentially the same as that of the Dow method. Bilirubin (up to 0.17 g/L), hemoglobin (up to 4 g/L), and slight lipemia (triglycerides up to 5.4 g/L) did not interfere with the aca method.

Autoanalysis↗

PubMed1982

Using the proposed NCCLS protocol for evaluation of automated instruments.

We compared four instruments (Sequential Multiple Analyzer Computer (SMAC), AutoAnalyzer II (AAII), StatLyte, and PVA-4) for the determination of Na, K, Cl and CO2 using a protocol (PSEP-1) of the National Committee for Clinical Laboratory Standards (NCCLS) for evaluation of precision and accuracy of automated instruments. The protocol was applied concurrently to all four instruments. NCCLS has revised this protocol into three separate protocols by which the manufacturer can make performance claims. Protocols specifically aimed at the user are now under development. Although PSEP-1 is no longer in use, many parts of it have been incorporated into PSEP-2, PSEP-3 and PSEP-4. This article will describe the adaptation of the protocol to evaluate four automated instruments in our laboratory.

Autoanalysis↗

PubMed1982

Four methods for determining uric acid compared with a candidate reference method.

Uric acid as measured in serum by three different uricase (EC 1.7.3.3) methods (aca, Ektachem, and SMAC) and by the SMAC method with phosphotungstic acid was compared with a candidate Reference Method for uric acid. Serum specimens from 83 patients (uric acid concentrations, 19 to 141 mg/L) were analyzed by all five methods. Results were compared by using linear regression analysis, and the mean difference between results by the candidate Reference Method and the four other methods was calculated. Compared with the candidate Reference Method, the aca method gave the smallest deviation from zero for the intercept and the smallest mean difference, and the SMAC phosphotungstic acid method showed a slope closest to unity. The SMAC uricase method had the largest intercept and greatest deviation of the slope from unity.

Autoanalysis↗

PubMed1980

Comparison of four electrolyte instruments using the proposed NCCLS protocol for evaluation of precision and accuracy of automated instruments.

We compared four instruments, [Sequential Multiple Analyzer Computer (SMAC), AutoAnalyzer II (AAII), StatLyte and PVA-4] for the determination of Na, K, Cl and CO2 using the National Committee for Clinical Laboratory Standard's (NCCLS) protocol (PSEP-1) for evaluation of precision and accuracy of automated instruments. The protocol was applied concurrently to all four instruments. The repeatability results showed SMAC to have the highest precision among-days for K, Cl, and CO2 whereas StatLyte showed the highest precision among-days for Na. The PVA-4 had the best within-run precision for Na and Cl while the AAII and SMAC had the best within-run precision for K and CO2 respectively. Systematic biases among the instruments were small for Na and K. The AAII exhibited a nearly constant bias at all concentrations of Cl relative to the other three instruments. For CO2 the SMAC showed a large proportional bias compared with the other three instruments.

Autoanalysis↗