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N Gochman

Publications and source records attributed to N Gochman.

14 recordsLinked to original sources
PubMed1979

Incorrect least-squares regression coefficients in method-comparison analysis.

The least-squares method is frequently used to calculate the slope and intercept of the best line through a set of data points. However, least-squares regression slopes and intercepts may be incorrect if the underlying assumptions of the least-squares model are not met. Two factors in particular that may result in incorrect least-squares regression coefficients are: (a) imprecision in the measurement of the independent (x-axis) variable and (b) inclusion of outliers in the data analysis. We compared the methods of Deming, Mandel, and Bartlett in estimating the known slope of a regression line when the independent variable is measured with imprecision, and found the method of Deming to be the most useful. Significant error in the least-squares slope estimation occurs when the ratio of the standard deviation of measurement of a single x value to the standard deviation of the x-data set exceeds 0.2. Errors in the least-squares coefficients attributable to outliers can be avoided by eliminating data points whose vertical distance from the regression line exceed four times the standard error the estimate.

Blood Chemical Analysis↗
PubMed1979

Maltotetraose as a substrate for enzyme-coupled assay of amylase activity in serum and urine.

The use of maltotetraose ss a new substrate for the enzyme-coupled determination of amylase activity in biological fluids was developed by Beckman Microbics. We evaluated a manual and a centrifugal analyzer version of the method in comparison with two commonly used manual starch-dye amylase techniques: Roche Amylochrome and Pharmacia Phadebas. Both maltotetraose amylase procedures proved to be rapid and precise, and results correlated satisfactorily with the starch-dye methods for serum and urine samples.

Amylases↗
PubMed1978

Continuous-flow enzymic method evaluated for measurement of serum triglycerides with use of an improved lipase reagent.

We compared a modified enzymic continuous-flow method for serum triglycerides, in which a microbial lipase is used without protease, to an extraction-fluorometric method. Results (for total--blank) correlated well with those by the comparison procedure: enzymic = 1.002 fluorometric--14 mg/liter; r = 0.9968. Serum blanks were measured for each sample in both methods, and the concentration of free glycerol measured by the enzymic method was shown to be as much as 15 to 71% of the total triglyceride result in 7% of the samples analyzed. The dual-channel continuous-flow system provides automatic free-glycerol blank subtraction for the enzymic method.

Fluorometry↗
PubMed1977

Characteristics of binding between reagent-strip indicators and urinary proteins.

We describe the binding characteristics of two indicator dyes that are widely used in commercial "dip-stick" indicators for protein in urine. Binding was studied by both gel filtration chromatography and by spectrophotometric titrations. The results demonstrate that the well-known lack of sensitivity of these strips to proteins other than albumin relates to the number and affinity of binding sites on these proteins as compared to albumin. The data suggest that these test strips can screen more effectively for albuminuria than for other proteinurias.

Chromatography, Gel↗
PubMed1976

Serum alpha-fetoprotein. A prognostic indicator of liver-cell necrosis and regeneration following experimental injury by galactosamine in rats.

The serum concentrations of alpha-fetoprotein of rats following experimental galactosamine-induced liver-cell necrosis accurately reflect the severity of preceding liver-cell damage as determined by elevation of serum transaminases. There is a very close correlation between the highest SGOT or SGPT serum activity found 1-2 days after induction of necrosis and the subsequent elevation of alpha-fetoprotein at 2-6 days. Elevations of alpha-fetoprotein are associated in time with restitutive proliferation of the damaged liver. These experimental results clarify the temporal relationship between alpha-fetoprotein and repair of liver-cell damage, which has been suggested by similar observations in cases of patients who have acute or sub-acute viral hepatitis. The correlations support the concept that serum alpha-fetoprotein concentrations may be used as a prognostic indicator of the extent and course of fulminatn or subacute hepatitis.

Alanine Transaminase↗
PubMed1976

Development of an aqueous temperature-indicating technique and its application to clinical laboratory instrumentation.

We describe a new technique for monitoring intra-cuvette temperatures in temperature-controlled spectrophotometric cells by use of two solutions, one for which absorbance is highly sensitive to temperature and one for which absorbance is insensitive to temperature. The first solution, cresol red in tris(hydroxymethyl)aminomethane buffer, is used to construct an absorbance-vs.-temperature calibration curvae. The second solution, cresol red in sodium hydroxide, is used for optical calibration of the spectrophotometric system to be tested. The combination of these two procedures allows accurate estimation of temperature. We show how this technique is applied to temperature measurement in several types of laboratory instrumentation.

Autoanalysis↗
PubMed1976

Cholesterol oxidase-based determination, by continuous-flow analysis, of total and free cholesterol in serum.

We describe a continuous-flow, automated determination of total cholesterol in serum, which is based on enzymatic hydrolysis of cholesterol esters, oxidation of cholesterol by cholesterol oxidase, and colorimetric measurement of liberated perioxide with 4-aminoantipyrine, phenol, and peroxidase. Free cholesterol is determined with the same AutoAnalyzer II manifold and reagents, except that cholesterol esterase is omitted from the reagent. Cholesterol-in-serum materials that have been assayed by an established method are used for calibration. We found this approach to be necessary because primary cholesterol standards in organic solvents are incompatible with the aqueous reagent. Results of the enzymatic total cholesterol method correlated well with those by an AutoAnalyzer II method which involves an extraction with isopropanol and the Liebermann-Burchard color reaction (total cholesterol, g/liter, yenz= 0991xlb +0.05;r=0.996). Results of the enzymatic free cholesterol procedure agreed satisfactorily with one in which free cholesterol is precipitated as the digitonide and subsequently analyzed colorimetrically with the Liebermann-Burchard reaction (free cholesterol, %, yenz = 0.982xdig -0.7;r= 0.956).

Autoanalysis↗
PubMed1975

Interlaboratory comparison of enzymatic methods for serum glucose determination.

This report describes an interlaboratory comparison of enzymatic serum glucose methods as currently applied in several instrumental adaptations. Four spectrophotometric, hexokinase-based methods used with the Du Pont "aca," the Abbott "Bichromatic Analyzer," the Aminco "Rotochem," and the Technicon "AutoAnalyzer ll" were compared with glucose oxidase-based methods as used with the Beckman "Glucose Analyzer" and the "AutoAnalyzer ll." We analyzed both normal samples and samples that contained potential interfering substances or were otherwise abnormal. Although all methods were satisfactorily precise, methodological bias was noted in several cases, particularly with abnormal specimens. The hexokinase-based methods were generally more variable. The most consistent data were obtained from the two glucose oxidase methods and the Du Pont aca. Results of this study comprise part of the background information required for development of an accurate glucose reference method under the auspices of the AACC Standards Committee.

Autoanalysis↗