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G N Bowers

Publications and source records attributed to G N Bowers.

At least 19 recordsLinked to original sources
PubMed1995

History of NIST's contributions to development of standard reference materials and reference and definitive methods for clinical chemistry.

The issuance of cholesterol as a Standard Reference Material (SRM) in 1967 started the National Institute of Standards and Technology (NIST; then named the National Bureau of Standards) on a major effort to help clinical laboratories establish and improve the quality of measurements they make. NIST now issues three kinds of SRMs for that purpose: analyte samples of certified purity as primary standards, serum samples having certified analyte concentrations as accuracy controls, and materials certified for calibrating instruments. In working with clinical laboratory scientists to establish Reference Methods (RMs) for measuring the analytes, NIST developed Definitive Methods (DMs) to use for evaluating RM accuracy and then used the DMs for assigning analyte values to its SRMs. The development of SRMs and DMs is discussed.

Blood↗
PubMed1993

Isotope dilution mass spectrometry and the National Reference System.

The clinical laboratory community of the United States, which is well represented by the NRSCL/NCCLS, has endorsed the IDMS/DMs developed at NIST. These DMs provide the accuracy (true value) base for the U.S. National Reference System for a number of specific analytes in human serum. Fortunately, the U.S. government through (a) actions of NIST administrators and scientists, (b) financial support from NIH (NIGMS) and FDA, and (c) interagency agreements with CDC has accepted the responsibility for developing and maintaining IDMS/DMs for clinically important analytes as an essential part of this national measurement system infrastructure. Furthermore, it is important to note that several professional organizations, particularly, The American Association for Clinical Chemistry (AACC) and The College of American Pathologists (CAP), have interacted heavily with NIST in full support of these national standardization activities. CAP supports three full-time Research Associates at NIST so that target values on serum samples used in its Interlaboratory Comparison Survey Programs may be traced to DMs. This remarkable cooperation and teamwork between government agencies and private sector organizations, as well as numerous individual scientists and physicians, which promotes greater accuracy of patient results, depends heavily upon the continued timely availability of IDMS/DM measurements. In short, NIST's value assignments on human serum samples (e.g., SRMs and materials for CLIA '88 proficiency testing programs) by this critical IDMS/DM metrology provide the pragmatic base for assuring accurate test results in medicine. The resources required to support IDMS/DM technology at NIST over many decades are not trivial and from time to time require renewed R&D efforts to upgrade methodology and recapitalization in mass spectrometry instrumentation.

Blood Chemical Analysis↗
PubMed1992

Investigation of N-methyl-D-glucamine buffer for assay of alkaline phosphatase in serum.

We evaluated N-methyl-D-glucamine (MEG) as a buffer for assay of alkaline phosphatase (ALP; EC 3.1.3.1) and compared the MEG-based assay with the current International Federation of Clinical Chemistry Reference Method for ALP (IFCC/RM/ALP), in which 2-amino-2-methyl-1-propanol (AMP) is the pH buffer. The ALP assay in MEG at 30 and 37 degrees C shows excellent correlation with the IFCC/RM/ALP at 30 degrees C, but yields proportionately higher ALP activities (8.2% at 30 degrees C and 57% at 37 degrees C). ALP is unstable in both MEG and AMP at 37 degrees C. Serum incubated in MEG undergoes a pH-dependent biphasic loss of ALP activity: an initial rapid 5% loss after 1 min of incubation and a 10% loss per hour thereafter. A similar pattern was seen for incubation with AMP. The use of a serum-initiated reaction (no preincubation of enzyme with buffer) eliminated the early loss in activity. The addition of the metal ion buffer N-hydroxyethylethylenediaminetriacetic acid, along with low concentrations of Zn and Mg, as used in the IFCC/RM/ALP, reduced the slow loss in activity over time, as did decreasing the reaction temperature to 30 degrees C, but had no effect on the early rapid decay in activity seen in the first minute. Moderate transphosphorylation (45%) and nonenzymatic hydrolysis (3.3 U/L) were observed with MEG under the conditions of the assay (37 degrees C). A comparison of different lots of MEG from two manufacturers showed no significant difference in ALP activities.

Alkaline Phosphatase↗
PubMed1992

Design and preliminary performance characteristics of a newly proposed reference cell for ionized calcium in serum.

A novel flow-through design for a calcium ion-selective liquid membrane and half-cell is proposed. The membrane is based on a neutral carrier for calcium and has the same quantitative chemical composition as that used in most commercial analyzers for ionized calcium (iCa2+). The membrane and half-cell follow the specifications in the Stage 1, Draft 4 document for a Reference Method for iCa2+ of the IFCC Expert Panel on pH, Blood Gases, and Electrolytes. Measurements of iCa2+ in serum with this cell confirm prior observations that protein adsorption on the membrane surface causes a rapid but reversible shift in the cell calibration signal and possible systematic errors in the measurement of iCa2+ in serum. When the protein adsorption phenomenon is maintained at equilibrium during calibrations and sample measurements, the new cell can be used to reproducibly assign iCa2+ concentrations to serum pools. These calibrated pools may then be used as reference materials and to resolve the biases known to exist among commercial iCa2+ analyzers.

Calcium↗
PubMed1990

Proposed reference method for iron in serum used to evaluate two automated iron methods.

The manual Reference Method of the Centers for Disease Control for serum iron (CDC/RM/Fe) and a semiautomated adaptation of it were used to evaluate two working methods: one, a detergent solubilization procedure for the Roche Cobas-Bio analyzer, the other, the Kodak Ektachem 700 procedure, based on dry-film technology. The CDC/RM/Fe and its semiautomated version gave essentially the same results for 40 sera from hospital patients. This semiautomated version was in turn compared with the two working procedures in a study involving 200 patients. Each of the working methods correlated well with the semiautomated CDC/RM/Fe method. Separate recovery and interference studies indicated satisfactory analytical recovery of iron in all cases, but the detergent solubilization method was found to be susceptible to interference by hemoglobin, lipemia, and bilirubin.

Autoanalysis↗
PubMed1990

Quality management science in clinical chemistry: a dynamic framework for continuous improvement of quality.

Current quality assurance approaches will not be adequate to satisfy the needs for quality in the next decade. Quality management science (QMS), as evolving in industry today, provides the dynamic framework necessary to provide continuous improvement of quality. QMS emphasizes the importance of defining quality goals based on the needs and expectations (implied needs) of customers. The laboratory can develop customer-friendly goals and measures of quality by recognizing that customers' experiences are represented by a totality of results. Quality goals and measures are best communicated as "total performance" by specifying a limit and percentile of the distribution, rather than a mean and standard deviation. Application of quality goals within the laboratory will usually require partitioning the total performance goal into components and translating those components into specifications to guide the operation and management of production processes. QMS also extends beyond technical processes to people processes and provides guidance for improving the quality of worklife and caring for the laboratory's most essential resource--our people.

Chemistry, Clinical↗
PubMed1990

Evaluation of three first-generation ion-selective electrode analyzers for lithium: systematic errors, frequency of random interferences, and recommendations based on comparison with flame atomic emission spectrometry.

Ion-selective electrode analyzers for measuring lithium (Li/ISE) in serum became available in early 1987. We compared results for patients' samples from three of them vs results from flame atomic emission spectrometry (FAES). Within-run and day-to-day imprecision ranged from 0.01 to 0.03 mmol/L and 0.01 to 0.04 mmol/L, respectively. Comparing Li/ISE results (y) with the FAES results (x) gave the following equations: y = 1.063x - 0.035 for AMDEV's Lytening 2, y = 1.020x + 0.038 for NOVA's Model 11, and y = 1.030x - 0.027 for AVL's Model 985. Unexplained positive errors greater than 0.2 mmol/L were observed for two of the 90 patients' samples, but only a few additional excessively high values were seen in 3000 patients' samples run subsequently (Lytening 2). Causes of error in clinical Li/ISE measurements are still unclear; simply characterizing them as "matrix effects" does not correct the underlying analytical problem. An increase in pH from loss of CO2 gave low results on two of the three Li/ISE analyzers but did not change FAES results. Trimethylammonium bicarbonate used in a reconstitution solution caused extremely high Li/ISE results but did not change FAES results. Performance specifications to help reduce and correct these errors are recommended.

Chemistry, Clinical↗
PubMed1989

The National Reference System for Cholesterol.

The NRS/CHOL is a reality that is progressively becoming the way in which accuracy of cholesterol results is being ensured. Proof of traceability to NRS/CHOL within each segment of the clinical laboratory, now an expectation, will soon be the norm that makes a sound conceptual reference system into an everyday reality that reaches into the many thousands of working sites that measure cholesterol in serum on patient samples.

Cholesterol↗
PubMed1989

Evaluation of a kinetic method for prostatic acid phosphatase with use of self-indicating substrate, 2,6-dichloro-4-nitrophenyl phosphate.

The purity, spectral characteristics, and rate of nonenzymatic hydrolysis of 2,6-dichloro-4-nitrophenyl phosphate (DCNPP) were determined. Rates of DCNPP hydrolysis by prostatic acid phosphatase (PAP) and erythrocytic acid phosphatase (EAP) (both EC 3.1.3.2) were measured in the absence and in the presence of various alcohols. 1.5-Pentanediol was the most effective transphosphorylation agent for specifically enhancing the activity of PAP. 1,4-Butanediol also enhanced PAP activity but markedly inhibited EAP activity. Bovine and human serum albumin preparations also accelerated the hydrolysis of DCNPP. DCNPP can be used for the continuous or multipoint-rate assay of PAP.

Acid Phosphatase↗
PubMed1989

Evaluation of the IFCC reference method for alanine aminotransferase: spurious blank ALT activity due to contamination of D-alanine with L-alanine, and recommendations for a correction.

During an evaluation of the IFCC reference method for alanine aminotransferase (ALT, EC 2.6.1.2), we noted that the specimen blank activity reaction was markedly increased. Experience with five different lots of D-alanine from four commercial sources indicated that substantial and varying negative bias (up to -10%) could be introduced into the blank-corrected ALT activity, depending on the lot of D-alanine used. Although the IFCC procedure for ALT mentions the possibility of this L-alanine contamination, we believe that the degree of contamination in commercial reagents is underestimated. Analyzing the five lots of D-alanine for L-alanine, we found the magnitude of negative bias to be correlated directly with L-alanine contamination. Here, we describe a quick, sensitive assay based on coupled reactions of L-amino acid oxidase/peroxidase for quantifying L-alanine in the concentration range of 0-15 mmol/L without a sample-dilution step. Results by this alternative L-alanine assay agreed well with those recommended in the IFCC ALT procedure. Further examination suggested an even simpler solution to the L-alanine contamination problem, because we found no difference in the blank-corrected ALT activity determined in Tris HCl buffer, with or without D-alanine (free of L-alanine). We therefore propose that D-alanine be omitted from the IFCC reference ALT procedure.

Alanine↗
PubMed1988

Measurement of total calcium in biological fluids: flame atomic absorption spectrometry.

The measurement of total calcium (CaT) in biological fluids by flame atomic absorption spectroscopy (FAAS) is one of the more accurate yet practical methods available today. With attention to details at every analytical step, the imprecision of FAAS outlined above can be as low as +/- 0.01 mmol/liter at the 2.65 mmol/liter upper reference level of CaT found in the serum of healthy young adults (a CV of 0.4%). The accuracy of FAAS as judged by measurements of NBS/SRM #909, a lyophilized serum material carrying CaT values assigned by isotope dilution mass spectrometry, can be within +/- 1% (recovery of 99-101%) or less in skilled hands. As our brief section on application suggests, FAAS methods for CaT can be adopted to provide rapid and accurate results in many different biological fluids and tissues.

Animals↗
PubMed1988

Measurement of ionized calcium in biological fluids: ion-selective electrode method.

There is now a consensus that Ca2+ measurements are more physiologically and clinically meaningful than CaT measurements. Ca2+ in serum, plasma, whole blood, and other biological fluids can be measured by direct potentiometry with ion-selective electrodes and a number of reliable instruments are commercially available for this measurement. Several factors affect the Ca2+ concentration and must be carefully controlled for the results to be meaningful. The most important of these considerations are the anaerobicity of the sample, the need to concurrently measure pH, and the concentration of heparin, if whole blood or plasma samples are used. The calibration of the Ca2+ ISE is critical to the accuracy of the measurement. The matrix of the calibrator should match that of the sample as closely as possible, particularly in regard to ionic strength and liquid junction potential. The measurement of Ca2+ in urine is complicated by the wide variation in ionic strength encountered in this type of sample; thus, it is more meaningful to standardize the ISE in terms of Ca2+ activity instead of concentration. Instrumentally, the measure of copper in biological samples can be achieved with high accuracy, high precision, without background correction, and with minimum sample pretreatment if care is taken to carefully plan and implement all the critical steps in the analysis procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Measurement of ionized calcium in serum with ion-selective electrodes: a mature technology that can meet the daily service needs.

This article reviews key advances in ion-selective electrode technology that have made potentiometric measurements of ionized calcium (Ca2+) reliable and precise. Our use of two second-generation Ca2+ analyzers (Radiometer ICA1 and NOVA 8) made possible uninterrupted service as volume increased to 31 640 patient tests in 1985. The lower results on the NOVA 8 were adjusted upwards to match those of the ICA1 to give identical results. Both analyzers were evaluated under working conditions of high volumes and multiple operators to establish downtime, electrode life, and costs. We have classified all Ca2+ analyzers into first-, intermediate-, and second-generation instruments, the better to understand their differences. Results for large numbers of patients' sera were shown to be systematically different when any two analyzers were compared. These differences are the consequence of each manufacturer's unique choices of the following: (a) the matrix of the calcium calibration solutions, (b) the type and configuration of the reference electrode, and (c) the salt-bridge solution. Elimination of each analyzer's biases will require agreement on a reference system that defines the accuracy of Ca2+ measurements on serum, plasma, or whole blood. The sound analytical performance of today's second-generation Ca2+ analyzers has allowed us to exploit the inherent superiority of Ca2+ over total calcium (CaT) measurements in the daily care of patients. We report on the preference of Ca2+ over CaT by physicians at our hospital since the introduction of second-generation Ca2+ analyzers. Therefore, we state unequivocally from our very satisfactory experience over the past five years that Ca2+ is a clinical laboratory test whose time has come!

Calcium↗