PubMed Health⌕ Search

Biomedical subjects

Gary L Myers

Publications and source records attributed to Gary L Myers.

At least 19 recordsLinked to original sources
PubMed2006

Automated method for measuring globin adducts of acrylamide and glycidamide at optimized Edman reaction conditions.

The general population is exposed to acrylamide, a potential human carcinogen, through food and cigarette smoke. The assessment of human exposure to acrylamide is important in the evaluation of health risks associated with this chemical. Hemoglobin adducts of acrylamide (AA-Hb) and its primary metabolite glycidamide (GA-Hb) are established biomarkers of acrylamide exposure and methods to measure these biomarkers using modified Edman reaction are described. Only limited information about the optimal Edman reaction conditions such as pH or temperature is available for these adducts and the existing methods do not allow automation needed in biomonitoring studies. In this study, the yield of Edman products of AA-Hb and GA-Hb between pH 3-10 and at 35-55 degrees C at different time intervals, and the applicability of liquid-liquid extraction on diatomaceous earth for analyte extraction, were assessed and results were used in a new optimized method. The applicability of our optimized method was assessed by comparing results obtained with a convenience sample from 96 individuals with a conventional method. Maximum yield of Edman products was obtained between pH 6-7, heating the reaction solution at 55 degrees C for 2 h resulted in the same yields as with conventional conditions, and use of diatomaceous earth was found suitable for automated analyte extraction. Using these conditions, no difference was observed between our optimized and a conventional method. The median globin adduct values in the convenience sample are 129 pmol/g globin (range: 27-453 pmol/g globin) and 97 pmol/g globin (range: 27-240 pmol/g globin) for AA-Hb and GA-Hb, respectively. The GA-Hb/AA-Hb ratio decreases significantly with increasing AA-Hb values indicating that measurement of AA-Hb as well as GA-Hb are needed to appropriately assess human exposure to acrylamide.

Acrylamides↗
PubMed2006

An overview of inflammatory markers in type 2 diabetes from the perspective of the clinical chemist.

C-reactive protein (CRP), when measured by a highly sensitive method, is a measure of lowgrade, chronic inflammation and is an independent risk factor for type 2 diabetes (T2D) and cardiovascular disease (CVD). CRP also has the capacity to interact with other risk factors to increase the risk for T2D and CVD. Population distributions divided into tertiles provide the capacity to predict onset of T2D and associated CVD. Preanalytical as well as analytical sources of variation in high-sensitivity CRP (hsCRP) measurements need to be standardized in order for CRP results to be optimally useful. The Centers for Disease Control and Prevention and the American Heart Association have issued guidelines for clinical usefulness of hsCRP measurements. The Centers for Disease Control and Prevention has taken steps to standardize hsCRP assays by evaluating secondary reference materials to be used by manufacturers to calibrate their assays.

Biomarkers↗
PubMed2006

Assessment of trueness of a glucose monitor using interstitial fluid and whole blood as specimen matrix.

BACKGROUND: Interstitial fluid (ISF) is a specimen of increasing interest for glucose measurements because it can be obtained in a minimally invasive manner. Our previous study showed that sufficient ISF can be obtained using microneedles to measure glucose with a conventional electrochemical glucose monitor. The aim of this study was to assess the trueness of this glucose monitor using split-sample comparison with whole blood. We used ISF as specimen and our gas chromatography/mass spectrometry (GC/MS) method as reference. METHODS: We obtained 50 ISF samples and 40 whole blood samples from hairless Sprague- Dawley rats and analyzed for glucose by both methods. RESULTS: For whole blood, a non-significant bias of 5.7% (+/-2 SD: -54.9% to 66.3%) was determined. ISF glucose measurements showed a significant constant bias of 29.5% (+/-2 SD: -85.0% to 144%), which seems to be caused in part by the lack of red blood cells in ISF. The correlation coefficients were 0.782 and 0.679 for whole blood and ISF, respectively. CONCLUSIONS: The assessed electrochemical glucose monitor shows a close agreement with our GC/MS reference method for whole blood, for which this monitor was optimized. When glucose measurements are performed with ISF as matrix, the observed bias needs to be taken into consideration. Further studies are necessary to elucidate the reasons for the wide dispersion of data for ISF.

Animals↗
PubMed2006

The importance of metrological traceability on the validity of creatinine measurement as an index of renal function.

The glomerular filtration rate (GFR) is currently considered the best overall index of kidney function. The possibility that laboratories might routinely report an estimated GFR has become practically feasible with the development of a formula, the "four-variable" Modification of Diet in Renal Disease study (MDRD) equation that uses age, sex, race, and serum creatinine parameters. However, a limitation of this equation for general implementation in healthcare is related to the use of differently calibrated creatinine measurement procedures among laboratories. The only way to achieve universal implementation of the GFR prediction equation, with the associated clinical benefits for patients, is, therefore, to promote worldwide standardization of methods to determine creatinine, together with the introduction of a revised GFR-estimating equation appropriate for use with standardized creatinine methods.

Carbon Radioisotopes↗
PubMed2005

Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program.

BACKGROUND: Reliable serum creatinine measurements in glomerular filtration rate (GFR) estimation are critical to ongoing global public health efforts to increase the diagnosis and treatment of chronic kidney disease (CKD). We present an overview of the commonly used methods for the determination of serum creatinine, method limitations, and method performance in conjunction with the development of analytical performance criteria. Available resources for standardization of serum creatinine measurement are discussed, and recommendations for measurement improvement are given. METHODS: The National Kidney Disease Education Program (NKDEP) Laboratory Working Group reviewed problems related to serum creatinine measurement for estimating GFR and prepared recommendations to standardize and improve creatinine measurement. RESULTS: The NKDEP Laboratory Working Group, in collaboration with international professional organizations, has developed a plan that enables standardization and improved accuracy (trueness) of serum creatinine measurements in clinical laboratories worldwide that includes the use of the estimating equation for GFR based on serum creatinine concentration that was developed from the Modification of Diet in Renal Disease (MDRD) study. CONCLUSIONS: The current variability in serum creatinine measurements renders all estimating equations for GFR, including the MDRD Study equation, less accurate in the normal and slightly increased range of serum creatinine concentrations [<133 micromol/L (1.5 mg/dL)], which is the relevant range for detecting CKD [<60 mL.min(-1).(1.73 m2)(-1)]. Many automated routine methods for serum creatinine measurement meet or exceed the required precision; therefore, reduction of analytical bias in creatinine assays is needed. Standardization of calibration does not correct for analytical interferences (nonspecificity bias). The bias and nonspecificity problems associated with some of the routine methods must be addressed.

Calibration↗
PubMed2005

Variability among five over-the-counter blood glucose monitors.

BACKGROUND: The American Diabetes Association recommends that people with diabetes use self-monitoring to control their blood glucose concentration. To assess the need for standardization, we evaluated the variability among 5 of the most common monitors: MediSense Precision Xtra, Ascencia Dex, Prestige Smart System, OneTouch Ultra, and Accu-Chek Advantage. METHODS: We took steps to minimize preanalytical variation. We also eliminated user variability by using one trained operator to collect samples and perform all testing. Each monitor was used twice with each participant; one test was performed using an aged strip and the other using a fresh strip. We compared monitors using a separate ANOVA for each concentration range and strip lot. RESULTS: The total CVs and the within-strip lot CVs were not statistically different among monitors, ranging from 3.1% to 11.3% and from 2.1% to 8.5%, respectively. There were statistically significant differences among monitors for among-strip lot CVs, which ranged from nearly 0% to 7.5%. The degree of significance increased as the concentration range increased [3.9-5.5 mmol/l: p<0.05; 5.6-7.7 mmol/l: p =0.003; 7.8-11.1 mmol/l: p < 0.001]. The average percent difference between monitor pairs was statistically significant (p < 0.05) in more than half of the paired comparisons, with significant differences ranging from 5.7% to 32.0%. CONCLUSIONS: Monitor results can vary significantly so that agreement among them is poor. Standardization is necessary to minimize variability and to improve patient care.

Adult↗
PubMed2005

Assessment of microwave-assisted enzymatic digestion by measuring glycated hemoglobin A1c by mass spectrometry.

Enzymatic digestion of proteins and analysis of the resulting peptides by mass spectrometry is an established approach in proteomics and in clinical and environmental chemistry. The long digestion times of several hours prevent the fast turnover of samples and results. Qualitative applications showed that microwave radiation profoundly shortens enzymatic digestion. However, its usefulness for quantitative applications had not been assessed. In this study, the microwave-assisted enzymatic digestion of hemoglobin at different temperatures, buffer concentrations, and digestion times was assessed and compared with conventional digestion for the proteolytic enzymes trypsin and Glu-C. A microwave-assisted enzymatic digestion method optimized for digestion time and temperature was applied for the analysis of glycated hemoglobin HbA1c and compared with a reference method. Using trypsin, complete digestion was obtained at 50 degrees C within 20 min. Under these conditions, the digestion efficiency was 20% higher than with conventional trypsin digestion. These effects were not observed with Glu-C as enzyme, probably because of the decreased stability of Glu-C at elevated temperatures in comparison with the trypsin used. The comparison of the optimized microwave-assisted digestion method using trypsin with the reference method for HbA1c using Glu-C gave a close correlation in the results (R2: 0.996). A significant bias of 0.33% HbA1c was observed, with higher values obtained with the microwave-assisted tryptic digest; this finding might have resulted from the use of a different enzyme. This study showed that microwave-assisted enzymatic digestion can substantially reduce digestion times to minutes and can be used in qualitative as well as quantitative applications.

Catalysis↗
PubMed2005

Pilot study on the impact of potato chips consumption on biomarkers of acrylamide exposure.

Food is assumed to be one major source of acrylamide exposure in the general population. Acrylamide exposure is usually assessed by measuring hemoglobin adducts of acrylamide and its primary metabolite glycidamide as biomarkers. Little is known about the impact of acrylamide in food on biomarkers of acrylamide exposure. Therefore, CDC is conducting a feeding study to investigate the effect of consumption of endogenous acrylamide in food on biomarkers of acrylamide exposure. As part of this study, we performed a pilot study to obtain further information on the magnitude of the changes in biomarker levels after consumption of high amounts of potato chips (21 ounces) over a short period of time (1 week) in non-smokers. After 1 week, biomarkers levels increased up to 46% for acrylamide adducts and 79% for glycidamide adducts. The results indicate that changes in biomarker levels due to consumption of potato chips can be detected. However, because of the design of this pilot study, the observed magnitude of change cannot be. generalized and needs to be confirmed in the main study.

Acrylamide↗
PubMed2005

Assessment of trueness of glucose measurement instruments with different specimen matrices.

BACKGROUND: The trueness of glucose monitors is commonly assessed using whole-blood samples and a clinical analyzer as a comparison method. In this study, the effect of specimen matrix on trueness of one clinical analyzer and one glucose monitor was compared with a gas chromatography-mass spectrometry (GC/MS) reference method, using split-sample comparison with capillary whole blood (CWB), venous whole blood (VWB), and plasma (PL). METHODS: CWB was analyzed by the glucose monitor and the GC/MS reference method. VWB was analyzed by the glucose monitor, clinical analyzer, and the GC/MS method. PL was analyzed by the clinical analyzer and the GC/MS reference method. RESULTS: For the glucose monitor, the bias was 0.4% and -18.2% for CWB and VWB, respectively. The clinical analyzer had a bias of -25.4% for VWB and -12.0% for PL and a proportional bias was detected in both specimens. Using the clinical analyzer as a comparison method, the glucose monitor had a proportional bias of -9.8%. CONCLUSION: The trueness of clinical analyzers can be affected by the specimen matrix that needs to be assessed before they are used as comparison method to assess trueness of glucose monitors.

Blood Glucose↗
PubMed2005

Creatinine measurement: state of the art in accuracy and interlaboratory harmonization.

CONTEXT: The National Kidney Disease Education Program recommends calculating glomerular filtration rate from serum creatinine concentration. Accurate creatinine measurements are necessary for this calculation. OBJECTIVE: To evaluate the state of the art in measuring serum creatinine, as well as the ability of a proficiency testing program to measure bias for individual laboratories and method peer groups. DESIGN: A fresh-frozen, off-the-clot pooled serum specimen plus 4 conventional specimens were sent to participants in the College of American Pathologists Chemistry Survey for assay of creatinine. Creatinine concentrations were assigned by isotope dilution mass spectrometry reference measurement procedures. PARTICIPANTS: Clinical laboratories with an acceptable result for all 5 survey specimens (n = 5624). RESULTS: The fresh frozen serum (FFS) specimen had a creatinine concentration of 0.902 mg/dL (79.7 micromol/L). Mean bias for 50 instrument-method peer groups varied from -0.06 to 0.31 mg/dL (-5.3 to 27.4 micromol/L), with 30 (60%) of 50 peer groups having significant bias (P < .001). The bias variability was related to instrument manufacturer (P < or = .001) rather than method type (P = .02) with 24 (63%) of 38 alkaline picric acid methods and with 6 (50%) of 12 enzymatic methods having significant biases. Two conventional specimens had creatinine concentrations of 0.795 and 2.205 mg/dL (70.3 and 194.9 micromol/L) and had apparent survey biases significantly different (P < .001) from that of the FFS specimen for 34 (68%) and 35 (70%) of 50 peer groups, respectively. CONCLUSIONS: Thirty of 50 peer groups had significant bias for creatinine. Bias was primarily associated with instrument manufacturer, not with type of method used. Proficiency testing using a commutable specimen measured participant bias versus a reference measurement procedure and provided trueness surveillance of instrument-method peer groups.

Bacteriological Techniques↗
PubMed2004

Distribution and correlates of C-reactive protein concentrations among adult US women.

BACKGROUND: Understanding the distribution of C-reactive protein (CRP) concentration among adult women in the US helps to establish the magnitude of women at increased risk for cardiovascular disease. METHODS: We examined the distribution and correlates of CRP, using data from 2205 women >or=20 years of age from the National Health and Nutrition Examination Survey 1999-2000. CRP was measured with a high-sensitivity latex-enhanced turbidimetric assay. RESULTS: CRP concentration ranged from 0.1 to 296.0 mg/L (median, 2.7 mg/L). After exclusion of women with a CRP concentration >10 mg/L, the median was 2.2 mg/L. Approximately 25.7% of women, representing approximately 26.8 million women, did not report using hormone replacement therapy and had a CRP concentration >3.0 to 10 mg/L, a category considered to indicate high risk for cardiovascular disease. Multiple linear regression analysis included age, race or ethnicity, education, smoking status, total cholesterol concentration, triglyceride concentration, systolic blood pressure, waist circumference, and concentrations of glucose, insulin, c-peptide, and glycated hemoglobin. CRP concentration varied by race or ethnicity (Mexican American > white) and hormone replacement therapy (users > nonusers). In addition, significant and independent associations existed between CRP and waist circumference, total cholesterol and triglyceride concentrations, and systolic blood pressure but not age, smoking status, alcohol use, insulin concentration, glycated hemoglobin, and c-peptide concentration. CONCLUSION: Large numbers of US women have an increased concentration of CRP.

Adult↗