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Biomedical subjects

William L Roberts

Publications and source records attributed to William L Roberts.

At least 37 records · Page 2Linked to original sources
PubMed2005

Lifestyle-only intervention attenuates the inflammatory state associated with obesity: a randomized controlled study in adolescents.

OBJECTIVES: The primary goals were to understand the relationship among the inflammatory factors, C-reactive protein (CRP), interleukin-6 (IL-6), and fibrinogen, and indices of obesity in normoglycemic, insulin-resistant adolescents and to investigate the impact of a lifestyle-only intervention on these nontraditional risk factors for cardiovascular disease (CVD). STUDY DESIGN: Randomized controlled lifestyle-only intervention study in adolescents. Of the 21 adolescents studied, 15 obese subjects (body mass index [BMI] = 37.6 +/- 3.3 kg/m 2 ) were randomized to either a lifestyle intervention program or usual care. The lean controls were studied only at baseline. Analysis of variance (ANOVA) for repeated measures was used to study intervention effect and t test, one-way ANOVA, and discriminant function analysis for baseline comparisons. RESULTS: The intervention group maintained weight, whereas the control group gained weight (P = .02). A redistribution of body composition and a decrease in insulin resistance were observed. Elevated circulating concentrations of CRP, fibrinogen, and IL-6 were significantly reduced (all P <or=.02) in response to intervention, but not in controls. CONCLUSIONS: Modest lifestyle-only change in previously sedentary obese adolescents redistributes the parameters of body composition in the absence of weight loss and reverses, at least in part, the inflammatory state in association with an improvement of insulin resistance.

Adolescent↗
PubMed2005

Brief report: Free prostate-specific antigen test utilization. Consistency with guidelines.

BACKGROUND: The American Cancer Society and American Urologic Association recommend prostate cancer screening for average-risk men between the ages of 50 and 75 years using digital rectal examination and prostate-specific antigen (PSA) testing. Measuring the percent free PSA may improve test specificity for detecting prostate cancer when the total PSA is between 2.5 and 10 ng/mL. OBJECTIVE: To assess whether free PSA testing practices are consistent with published screening guidelines. DESIGN: Retrospective analysis of free PSA testing performed by a national reference laboratory between October 1, 2003 and September 30, 2004. MEASUREMENTS: Free PSA and total PSA results and the age of the patient at testing. RESULTS: Over 24% of free PSA tests were performed on patients greater than 75 years of age, and 38% were performed on patients with a total PSA either less than 2.5 ng/mL or greater than 10.0 ng/mL. CONCLUSIONS: A substantial proportion of free PSA tests performed in a national reference laboratory appeared to be inconsistent with existing screening guidelines. This raises concern that some of these patients may have received inappropriate diagnostic workup and/or therapy, resulting in excess medical costs and potential harms.

Aged↗
PubMed2005

Evaluation of a (1->3)-beta-D-glucan assay for diagnosis of invasive fungal infections.

The Fungitell assay (Associates of Cape Cod, Inc.) is a commercial test that detects (1-3)-beta-D-glucan (BG) and is intended for diagnosis of invasive fungal infections. To evaluate the Fungitell assay, we tested serum and plasma samples from healthy blood donors and from patients with blood cultures positive for yeast or bacteria. All 36 blood donors were BG negative, and 13 of 15 candidemic patients were BG positive. Of 25 bacteremic patients, 14 (10 with gram-positive bacteremia) were BG positive. One of the latter patients with Staphylococcus aureus bacteremia also had invasive candidiasis, based on histological findings in a tissue biopsy; therefore, the BG result was a true positive. The sensitivity, specificity, and positive and negative predictive values of the Fungitell assay, by patient, for these three groups were 93.3%, 77.2%, 51.9%, and 97.8%, respectively. We also performed the Fungitell assay on sera that had been tested for Aspergillus galactomannan or Histoplasma antigen. All six Histoplasma antigen-positive patients and 31 of 32 Aspergillus galactomannan-positive patients were also BG positive. BG results for the 10 Histoplasma antigen-negative and the 32 Aspergillus galactomannan-negative patients varied, but we were unable to confirm many of the results. Between-run coefficients of variance (CVs) for the assay ranged from 3.2% to 16.8%; within-run CVs were < or =4.8%. The correlation coefficient for an interlaboratory reproducibility study was 0.9892. Concentrations of hemoglobulin, bilirubin, and triglycerides that caused 20% interference were 588, 72, and 466 mg/dl, respectively. Our results suggest that the Fungitel assay may be most useful for excluding invasive fungal infection.

Aspergillosis↗
PubMed2005

Performance characteristics of an HPLC assay for urinary albumin.

Microalbuminuria is a marker of diabetic nephropathy and cardiovascular risk. Immunoassays underestimate the amount of intact albumin present in urine. The purpose of this study was to evaluate a new urinary albumin assay that uses size exclusion high-performance liquid chromatography (HPLC). We determined the limit of detection, linearity, imprecision, a comparison with an immunoturbidimetric assay, and pediatric and adult reference intervals. The limit of detection was 3.4 mg/L. The assay was linear from 4 to 240 mg/L. Total imprecision was less than 10% from 16 to 206 mg/L. Comparison of the albumin/creatinine ratio by HPLC with an immunoturbidimetric method showed positive proportional bias, which decreased with increasing concentrations of albumin. Nonparametric reference intervals were 22 to 250 mg/g for girls, 20 to 130 mg/g for boys, 14 to 62 mg/g for women, and 10 to 37 mg/g for men. This HPLC assay for urinary albumin shows acceptable performance and quantifies albumin species that are not detected by immunoassay. Separate reference intervals for children and adults seem necessary.

Adult↗
PubMed2005

Performance characteristics of four automated natriuretic peptide assays.

Measurement of circulating B-type natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) can identify patients with heart failure and guide therapy. The limit of detection, linearity, imprecision, method comparison, analytic concordance, and reference intervals of the Access 2 BNP (Biosite, San Diego, CA), ADVIA Centaur BNP (Bayer Diagnostics, Tarrytown, NY), AxSYM BNP (Abbott Diagnostics, Abbott Park, IL), and E170 NT-proBNP (Roche Diagnostics, Indianapolis, IN) methods were evaluated. The Triage meter BNP assay (Biosite) was the comparison method. Imprecision testing showed total coefficients of variation of 4.1%, 4.4%, 5.5%, and 0.8% for the Access 2, ADVIA Centaur, AxSYM, and E170, respectively. Relative to the Triage meter, method comparison revealed a slope of 0.96 and r = 0.95, a slope of 0.77 and r = 0.92, a slope of 1.13 and r = 0.94, and a slope of 8.8 and r = 0.80 for the Access 2, ADVIA Centaur, AxSYM, and E170, respectively. Overall analytic concordance values with the Triage meter were 95.9%, 92.9%, 92.4%, and 84.3% for the Access 2, ADVIA Centaur, AxSYM, and E170, respectively. All automated natriuretic peptide methods showed acceptable analytic performance.

Autoanalysis↗
PubMed2004

Analysis of plasma amino acids by HPLC with photodiode array and fluorescence detection.

BACKGROUND: Plasma amino acids are usually analyzed by ion-exchange chromatography (IEC), a reproducible but time consuming method. Here, we test whether plasma amino acids can be analyzed using reverse-phase high performance liquid chromatography (HPLC). METHODS: Filtered plasma, with S-carboxymethyl-l-cysteine as the internal standard, was derivatized and analyzed by an Agilent 1100 HPLC system. Primary amino acids were derivatized with o-phthalaldehyde 3-mercaptopropionic acid (OPA) and detected by a diode array detector. Secondary amino acids were derivatized with 9-fluorenylmethyl chloroformate (FMOC) and detected fluorometrically. Chromatographic separation is achieved by two gradient elutions (two injections per sample), starting at different pHs, on a reverse phase Agilent Zorbax Eclipse C(18) column AAA (4.6 x 150 mm). RESULTS: The HPLC method evaluated correlated well with IEC (0.89</=r</=1.00) with linearity up to 2500 mumol/l. The between- and within-run CVs were <6.0%. In addition, this method is able to separate argininosuccinic acid, homocystine and allo-isoleucine, rare but clinically significant amino acids. CONCLUSION: This HPLC method was comparable to IEC and could represent an alternative for amino acid analysis.

Amino Acids↗
PubMed2004

CDC/AHA Workshop on Markers of Inflammation and Cardiovascular Disease: Application to Clinical and Public Health Practice: laboratory tests available to assess inflammation--performance and standardization: a background paper.

Inflammation plays a key role in atherosclerosis. A number of different biomarkers of inflammation are measurable in blood. These include cytokines, chemokines, soluble adhesion molecules, and acute-phase reactants. The first 3 groups of molecules are not routinely measured in clinical laboratories. The acute-phase reactants include C-reactive protein (CRP). This analyte is stable and is readily measured by several commercial high-sensitivity (hs) assays, and numerous clinical studies have demonstrated its usefulness as an atherosclerotic risk marker. For these reasons, CRP is currently the inflammatory marker of choice. Comparison of commercial hsCRP assays has demonstrated that many are capable of imprecision of <7% at a CRP concentration of <1 mg/L. Method comparability studies have shown good agreement among some commercial hsCRP assays in terms of quartile assignments, whereas additional standardization efforts are necessary for others. The first goal of standardization is to develop a secondary reference material with a CRP of approximately 4 mg/L. This material can be used to assist diagnostic vendors in calibrator value assignment and assay harmonization. Another project is to define clearly what performance characteristics are necessary for hsCRP assays. Preliminary estimates based on the biological variability of CRP indicate that the total allowable analytical error is between 15% and 32%. The former requirement can be met with accuracy and imprecision of <5% and the latter requirement with accuracy and imprecision of <11%. If 2 hsCRP results are averaged, then the imprecision requirements are relaxed slightly. Clinical validation of these performance requirements is also required.

Acute-Phase Proteins↗
PubMed2004

Performance characteristics of six third-generation assays for thyroid-stimulating hormone.

BACKGROUND: Thyroid-stimulating hormone (TSH) is used to detect primary hypo- and hyperthyroidism. Current guidelines for TSH assays recommend a functional sensitivity of < or =0.02 mIU/L. The protocol for determining the functional sensitivity of TSH assays specifies analyses of serum samples with two reagent lots over a 6- to 8-week period. METHODS: We determined the functional sensitivities of the Access 2, ADVIA Centaur, ARCHITECT i2000, E170, IMMULITE 2000, and Vitros ECi automated methods, using seven serum pools and two reagent lots for each method. RESULTS: The observed functional sensitivities were as follows: Access 2, <0.020 mIU/L; ADVIA Centaur, 0.039 mIU/L; ARCHITECT i2000, <0.005 mIU/L; Elecsys E170, 0.011 mIU/L; IMMULITE 2000, 0.014 mIU/L; Vitros ECi, 0.004 mIU/L. However, there were large differences between some method means for the seven serum pools. For the pool with the lowest TSH concentration, mean results were as follows: Access 2, 0.0203 mIU/L; ADVIA Centaur, 0.0085 mIU/L; ARCHITECT i2000, 0.0049 mIU/L; E170, 0.0098 mIU/L; IMMULITE 2000, 0.0077 mIU/L; Vitros ECi, 0.0014 mIU/L. Method-comparison studies using samples with TSH concentrations >0.2 mIU/L also showed method differences. The ARCHITECT i2000 method was the most precise at low TSH concentrations. CONCLUSIONS: TSH methods do not provide comparable results for serum pools with TSH concentrations <0.2 mIU/L or for patient results across the analytic measurement range. Further investigation into the cause of these differences and additional harmonization efforts are required.

Autoanalysis↗
PubMed2004

Solid phase extraction procedure for urinary organic acid analysis by gas chromatography mass spectrometry.

We have developed a solid phase extraction procedure for the detection of organic acids by GC-MS using a strong anion exchange column (Sep-Pak Vac RC, Accell Plus QMA cartridge). Extraction efficiencies of 25 organic acids were established by analyzing standards in water based solutions. High extraction efficiencies (90 to 100%) were found for many of the compounds studied. We estimated the limit of detection for 48 organic acids and glycine conjugates. They were below 5 nmole with the exception of malonic and oxalic acids and mevalonic acid lactone. This method provides the advantage of higher recoveries for a wide range of compounds of interest and therefore can be a potential alternative to liquid-liquid extraction for organic acid screening. It is especially sensitive for the detection of some polar compounds, such as 3-OH-glutaric and N-acetylaspartic acids.

Acids↗
PubMed2004

Performance characteristics of the IMMUNLITE 2000 erythropoietin assay.

BACKGROUND: Erythropoietin (EPO) is a glycoprotein hormone produced by specialized cells in the kidney that acts as the primary regulator of erythropoiesis. Serum EPO measurements are useful for diagnostic evaluations of anemia and polycythemia. METHODS: The IMMULITE 2000 is an automated random access immunoassay analyzer for the central laboratory. The limit of detection (LOD), linearity, imprecision, comparison to another commercially available assay, and reference interval of a new EPO assay for this analyzer were assessed. RESULTS: The LOD was 0.2 U/l. The assay was linear within an allowable systematic error of 10% over the range tested (2-178 U/l). The total imprecision of the new assay was <7% for concentrations from 15.8 to 68.4 U/l. Comparison with the Advantage EPO assay method showed comparable results. Deming regression analysis gave a slope of 1.13+/-0.02, an intercept of -1.09+/-0.97, and a S(y/x) of 7.1 (r=0.99) over the range tested (2-200 U/l). CONCLUSIONS: The IMMULITE 2000 EPO assay shows acceptable performance and is suitable for routine clinical use.

Autoanalysis↗
PubMed2004

Performance characteristics of a recombinant enzymatic cycling assay for quantification of total homocysteine in serum or plasma.

BACKGROUND: Homocysteine is an amino acid that has been linked to an increased risk of coronary artery disease and stroke. A recombinant enzymatic cycling assay for homocysteine was evaluated using a Roche Modular Analytics P800 chemistry analyzer. METHODS: Bound homocysteine is released by disulfide reduction and combined with serine to form L-cystathionine that is degraded by cystathionine beta-lyase into homocysteine, pyruvate, and ammonia. Pyruvate is converted to lactate and the amount of NAD+ produced is directly proportional to the concentration of homocysteine. The limit of detection (LOD), linearity, imprecision, method comparison, reference interval and susceptibility to common interferences were assessed. RESULTS: The limit of detection was 0.31 micromol/l. The method was linear from 1 to 100 micromol/l with a maximum deviation from the target concentration of <10%. The total imprecision was <5.4% for homocysteine concentrations between 11.4 and 39.4 micromol/l. Method comparison was performed using an immunoassay on the ADVIA Centaur as the comparison method. Deming regression analysis gave a slope of 1.00, intercept of -0.75 and r=0.992. The mean bias relative to the ADVIA Centaur method was -0.9 micromol/l with limits of agreement of -5.0 and +3.5 micromol/l. The reference interval was 4.7 to 12.7 micromol/l. CONCLUSIONS: This enzymatic assay for homocysteine provides acceptable performance on the Modular Analytics P800 analyzer.

Automation↗
PubMed2004

Effects of beta thalassemia minor on results of six glycated hemoglobin methods.

BACKGROUND: Beta-thalassemia minor (BTM) is a common benign condition that can be present in patients with diabetes mellitus. There are conflicting reports about the effect of BTM on glycated hemoglobin (gHb) measurements. We evaluated 6 gHb methods using samples from non-diabetic subjects with BTM. METHODS: Samples submitted for hemoglobin phenotype analysis were evaluated. A total of 57 samples (30 controls and 27 with BTM) from non-diabetic subjects were selected. GHb analysis was performed by Tosoh A1c 2.2+, Primus CLC 330, Bayer DCA 2000, Beckman Coulter, Synchron CX7 and LX20, and Roche Tina-quant II assays. RESULTS: The A1c 2.2+, CLC 330, DCA 2000 and Tina-quant II assays showed no statistically significant difference between the control and BTM groups. In contrast, BTM results were significantly higher than controls on the Synchron CX7 analyzer and borderline significant on the Synchron LX20 (p=0.051). Further investigation demonstrated an increase in Synchron %HbA(1c) results with decreasing hemoglobin concentrations. CONCLUSIONS: In this study using samples from subjects with normal or near-normal gHb, BTM does not affect gHb measurements per se. However, the Synchron methods yielded higher results for samples with lower hemoglobin concentrations, like those that can be seen in BTM. The Synchron method was improved at the end of 2003, which minimized this problem.

Adult↗
PubMed2004

Cortisol and cortisone analysis in serum and plasma by atmospheric pressure photoionization tandem mass spectrometry.

OBJECTIVES: Cortisol metabolism is controlled by 11beta-hydroxysteroid dehydrogenase (11beta-HSD) isoenzymes, which interconvert cortisol and cortisone. Accurate measurement of the cortisol and cortisone concentrations and their ratio provide useful information about 11beta-HSD activity. METHODS: Cortisol and cortisone were extracted with methyl-tert-butyl ether from 100 microl of serum or plasma. The extract was evaporated, reconstituted with mobile phase, and analyzed by tandem mass spectrometry using a photoionization interface. The transitions monitored were: m/z 363 to 121 and 363 to 97 for cortisol, 361 to 163 and 361 to 105 for cortisone. RESULTS: Within-run and between-run coefficients of variation were less than 6% and 12%; 14% and 22%; 11% and 21% for cortisol, cortisone, and their ratio, respectively. The limit of detection was 1 microg/l for cortisol and 5 microg/l for cortisone. Normal ranges for cortisol and cortisone concentration and for their ratio in plasma (n = 120) determined as the central 95% were 33-246 microg/l for cortisol, 8-27 microg/l for cortisone, and 0.081-0.301 for the cortisone/cortisol ratio. CONCLUSIONS: We developed a simple sensitive method for cortisol and cortisone analysis in plasma and serum that uses a small sample volume. The method is very specific, fast, does not have any known interference, and is useful for diagnosis of variety of disease and pathologic conditions.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed2004

Performance characteristics of five automated serum cortisol immunoassays.

BACKGROUND: Serum cortisol measurements are used to help diagnose conditions of cortisol deficiency and excess. Automated, nonisotopic immunoassays are used in most clinical laboratories. METHODS: Linearity, imprecision, and method comparison studies for serum cortisol assays were performed with the Access, Advia Centaur, AxSYM, Elecsys 2010, and IMMULITE 2000 analyzers. RESULTS: All methods demonstrated acceptable linearity with the AxSYM method showing the least deviation from target values. The Elecsys 2010 method was the most precise for all three levels of quality control material. Method comparison studies demonstrated good concordance among methods except for two patient samples that gave results on the Elecsys 2010 that were significantly higher than the other methods. Differences in assay calibration were observed. CONCLUSIONS: Overall, all methods performed well. Additional calibration standardization efforts are required to truly harmonize the results from each assay. The Elecsys 2010 method is less specific than other automated methods based on two discordant patient results.

Autoanalysis↗