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Biomedical subjects

A E Hartmann

Publications and source records attributed to A E Hartmann.

14 recordsLinked to original sources
PubMed1993

Matrix effects on proficiency testing materials. Impact on accuracy of cholesterol measurement in laboratories in the nation's largest hospital system.

The objective of this collaborative study with the Department of Veterans Affairs (VA), College of American Pathologists (CAP), and the Centers for Disease Control and Prevention (CDC) was to quantitate the matrix-induced biases of cholesterol measurements on the CAP Comprehensive Chemistry Surveys materials used in proficiency testing (PT). A total of 174 VA Medical Centers outpatient clinics and clinical laboratories participate in the VA-CDC National Cholesterol Standardization and Certification Program. This study was conducted in 112 VA laboratories that have been standardized for measuring cholesterol accurately (within +/- 3.0% of the CDC reference-method values) using fresh, unfrozen, unadulterated human serum samples. Fresh serum samples and 1990 CAP Surveys materials were sent by overnight mail, and the laboratories were asked to analyze them simultaneously in triplicate in a single analytic batch run. The results showed significant matrix-effect biases with the CAP Surveys materials with six of the eight major peer groups, despite the fact that accuracy of cholesterol measurements was maintained with fresh serum samples. The magnitude and direction (positive or negative) of the matrix-effect biases were instrument, reagent, and method specific using the following peer groups: du Pont Dimension (-8.9%); Beckman CX4, CX5, and CX7 (-5.5%); Kodak Ektachem 400, 500, and 700 (+4.4%); Instrumentation Laboratory Monarch (-3.1%); Baxter Paramax (-2.4%); Technicon SMAC and RA (+1.3%); Hitachi/BMD 704 through 747 (+0.4%); and Abbott Spectrum (-0.3%). The CAP PT materials used currently do not behave in a manner identical to fresh human serum when measuring cholesterol on many, but not all, analytic systems. The observed biases due to "matrix effects" with PT materials will cause incorrect conclusions about the accuracy of many laboratory procedures performed on fresh patient specimens. This matrix-effect phenomenon will severely hamper interlaboratory accuracy transfer, standardization efforts, and monitoring performance of a laboratory's testing accuracy with the use of the current survey materials used in PT programs. Collaborative efforts are needed to (1) improve PT fluids to analytically behave more like fresh, human serum; (2) improve instrument design and reagent formulation; and (3) select methods and methodologic parameters that are more "robust" and less sensitive to the exact character of processed calibrators, quality control, and PT materials.

Bias↗
PubMed1992

The concept of establishing vs verifying analytic claims in method evaluations.

The establishment of analytic claims occurs during the method development stage. For commercial methods, the thorough characterization of analytic performance is the responsibility of the manufacturer. The manufacturer establishes performance claims with a high degree of certainty by utilizing statistically sound experimental protocols with sufficient degrees of freedom. The manufacturer should establish performance claims that state the expected performance of the method for the intended spectrum of patients and laboratory environment. The verification of analytic claims occurs by the end-user of the method. The end-user should not have to necessarily repeat the extensive protocol testing of the manufacturer that was used to establish the performance claims. The goals of the method verification study are not to establish analytic performance or to determine if the analytic performance is clinically acceptable, but, simply, to confirm or verify the stated established performance claims of the manufacturer. This implies an abbreviated method evaluation with statistical confirmation that analytic performance is acceptable. Analytic parameters that should be verified are imprecision, inaccuracy (bias), and linearity including analytic sensitivity. Reference ranges should be determined if the patient population is unique, or if the reference range of the analyte is relatively new or unstudied. Principles of method evaluation are discussed.

Chemistry, Clinical↗
PubMed1990

College of American Pathologists-Centers for Disease Control collaborative study for evaluating reference materials for total serum cholesterol measurements.

Several recent studies to evaluate the performance of laboratory instruments have shown that with some instrument systems processed (lyophilized, frozen, and stabilized) materials exhibit matrix effects that cause the assay for cholesterol to respond differently for them than for patient specimens. To understand this phenomenon better the College of American Pathologists, Northfield, III, and the Centers for Disease Control, Atlanta, Ga, have conducted a collaborative study with 44 laboratories where 16 instruments manufactured by nine companies are evaluated. The purposes were to assess measurement variation on several reference materials used for standardizing total cholesterol measurements and to evaluate a new stabilized liquid serum as a potential reference material. Lypophilized, frozen, fresh-frozen, and stabilized materials at three concentrations were measured for total cholesterol. The results show that the average coefficient of variation of measured total cholesterol for all instruments, laboratories, vials, and replicates is 3.6% to 4.1% for each of the materials measured (excluding the results for one instrument). For one instrument, however, significant bias was found on the stabilized liquid serum material. Results from the fresh-frozen materials indicate that the instrument systems evaluated allow laboratories to attain the National Cholesterol Education Program analytical performance goals.

Analysis of Variance↗
PubMed1985

Accuracy of participant results utilized as target values in the CAP Chemistry Survey Program.

Samples of lyophilized human serum were circulated to more than 7,000 participants in the College of American Pathologists chemistry survey program. The participants measured the concentrations of glucose, cholesterol, uric acid, and urea along with other constituents in the samples. Selected samples also were sent to the National Bureau of Standards (NBS) for analysis of these same analytes by definitive methods. Consensus mean values of participant results are used as target values. The participant values were compared with the NBS values, providing a measure of the accuracy of the designated target values. There was, in general, excellent correlation between the NBS definitive values and the designated target values. These target values can provide reliable reference points by which to evaluate participant performance.

Blood Glucose↗
PubMed1985

Accuracy of creatinine results reported by participants in the CAP Chemistry Survey Program.

This report summarizes the creatinine data reported by over 6,000 participants in the 1982 to 1983 College of American Pathologists Chemistry Survey Program. Participants analyzed lyophilized serum samples on a quarterly basis. The most widely used methods employed the kinetic alkaline picrate reaction. Selected samples also were analyzed at the National Bureau of Standards using an isotope dilution-mass spectrometry definitive method. The participant mean results of each method principle group showed positive biases to the definitive values. The kinetic alkaline picrate and enzymatic method groups had the least biases to the definitive values. Excellent correlations between these two method groups and the definitive values were demonstrated. The consensus mean values of these two method groups would provide reliable target values for creatinine in survey samples. Interlaboratory precision improved significantly in each method group as the creatinine concentration increased.

Creatine Kinase↗
PubMed1984

Evaluation of the ASTRA o-cresolphthalein complexone calcium method.

An automated calcium method based on o-cresolphthalein complexone chemistry and designed to be used in conjunction with the Beckman ASTRA systems (Beckman Instruments, Inc., Brea, CA) was evaluated. Day-to-day reproducibility studies yielded coefficients of variation ranging from 1.2 to 3.1%. Linearity was 5.0-15.5 mg/dL, and recovery of calcium averaged 98%. Bilirubin, creatinine, hemoglobin, and turbidity did not cause significant interference while there was a positive interference due to magnesium. The throughput is 70 samples per hour, and a single stat result can be obtained in 9 minutes from the standby mode. Very little sample (12 microL) or reagent (150 microL) is required. There was excellent correlation between the ASTRA calcium method and atomic absorption spectrophotometry (Y = 1.047x - 0.39, r = 0.9941). Analytic performance was judged acceptable according to Westgard's medical usefulness criteria of the observed total analytic errors being less than the limit of allowable error.

Autoanalysis↗
PubMed1982

Vial-to-vial variation of a stabilized liquid quality control serum.

The vial-to-vial variation of a new ethylene glycol stabilized liquid quality control serum (DecisionTM, Beckman Instruments, Inc.) was evaluated. Intervial variation was compared with intravial variation by analyzing multiple vials in duplicate for 22 different analytes at three different concentration levels. The data were examined the Anova statistics partitioning the total variance into the variance within bottle, and the variance between bottle. The F-statistic at P = 0.05 was used to assess the significance of the results. It was concluded that there is bottle to bottle homogeneity for the analytes studied. Other advantages of this liquid material are potential decreased wastage of material due to aliquoting only the required amount of serum, and increased savings in labor time due to elimination of reconstitution that is needed for lyophilized material.

Blood↗
PubMed1981

Long-term stability of a stabilized liquid quality-control serum.

To evaluate the long-term stability of a new liquid quality-control serum ("Decision", Beckman Instruments, Inc.) stabilized with ethylene glycol (330 mL/L), we analyzed it for 22 commonly measured analytes during storage at 2--8 degrees C for 24 days or -15 to -20 degrees C for 55 weeks. Three separate laboratories replicated the analyses, using various analytical methodologies. The data were subjected to linear regression analysis, regressing concentration on time. Analytes were considered unstable when the linear regression coefficient was unequal to zero with 95% or greater probability in all three laboratories. By this criterion all of the analytes were stable for at least 24 days when the control serum was stored at refrigerator temperature and for at least 55 weeks at freezer temperature. We conclude this material is a satisfactory substitute for existing lyophilized quality-control materials and offers certain advantages: stability, vial-to-vial uniformity, decreased waste, and eliminated reconstitution.

Blood Chemical Analysis↗
PubMed1980

Evaluation of the ASTRA 4 new microprocessor-controlled electrolyte analyzer.

A new programmable microprocessor-controlled multichannel chemistry analyzer, the Bechman ASTRA 4, was evaluated in an electrolyte configuration including sodium, potassium, chloride, and CO2. Sodium and potassium are analyzed with ion-selective electrodes, CO2 by differential rate pH measurement, and chloride by proportional coulometric titration, Day-to-day reproducibility studies yielded coefficients of variation of 0.8% for Na+, 1.2% for K+, 0.9% for Cl-, and 5.9% for CO2. Linearity was 100-200 mmol/l for Na+, 1.0-10.0 mmol/l for K+, 50-150 mmol/l for Cl+, and 5-50 mmol/l for CO2. There was excellent correlation between the ASTRA 4 and the comparison laboratory methodologies consisting of flame photometry, coulometry, and Beckman Chlorie/CO2 titrator. Performance of the ASTRA 4 was judged acceptable relative to requirements of medical usefulness. The instrument can be used as a routine electrolyte analyzer with a throughput of 60 samples an hour or as a stat analyzer with results obtained within 8.5 minutes. Each sample can be programmed for any combination of tests, and reagent is only consumed on those tests selected. Sample size is approximately 130 microliter for all four tests or reduced accordingly if fewer tests are selected.

Carbon Dioxide↗