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Biomedical subjects

William L Roberts

Publications and source records attributed to William L Roberts.

At least 55 records · Page 3Linked to original sources
PubMed2004

Comparison of two homogeneous HDL cholesterol methods in a large population study.

OBJECTIVES: High-density lipoprotein cholesterol (HDL-C) is an independent risk factor for coronary heart disease. Data are lacking on the performance of homogeneous methods using a large number of samples. DESIGN AND METHODS: We compared the performance of two HDL-C direct assays, the Dimension RxL (the Dade method) and the COBAS INTEGRA (the Roche method), for population screening. Performance was assessed using 4214 sera obtained from the International Collaborative Study on Atherosclerosis and Stroke In Asia (InterASIA) participants. RESULTS: The method comparison results demonstrated that both methods were highly correlated (r = 0.972). Deming regression analysis showed a slope of 1.009 +/- 0.007, an intercept of 0.048 +/- 0.009 and a S(y/x) of 0.08. The means were 1.29 +/- 0.33 and 1.23 +/- 0.33 mmol/l for the Roche and Dade methods, respectively, and the range of observed values were 0.30-3.05 and 0.19-2.86 mmol/l, respectively. The 95% confidence interval for the mean of the method differences was -0.10 to 0.22 mmol/l. Percentages of low (> or = 1.55 mmol/l), normal (1.03-1.54 mmol/l), and high risk (< 1.03 mmol/l) results were 15.5, 55.4, 29.0 for the Dade and 19.3, 59.3, 21.4 for the Roche method. The percentage of concordantly classified subjects at each cut point was 77.1%, 84.4%, and 95.5%. The percentage of overall consistency subjects was 85.4%. Thirteen percent of subjects were discordantly classified into the higher-risk group while the 1.6% of subjects were discordantly classified into the lower-risk group. CONCLUSIONS: Both homogeneous HDL-C methods were correlated and agree well with one another. The percentage of concordantly classified subjects was high. Thus, either method is suitable for large population studies.

Blood Chemical Analysis↗
PubMed2004

Performance characteristics of eight estradiol immunoassays.

Measurement of estradiol is useful in assisted reproduction, evaluation of infertility, menopause, and male feminization. The analytic performance of 8 estradiol immunoassays was evaluated. The imprecision and accuracy of the Access, ADVIA Centaur, ARCHITECT i2000, AutoDELFIA, Elecsys 2010, IMMULITE 2000, and Vitros ECi estradiol assays (see text for proprietary information) were evaluated by using an isotope dilution-gas chromatography-mass spectrometry (ID-GC-MS) reference method. The coefficient of variation (CV) ranged from 6.9% on the Elecsys 2010 to 42.6% on the ADVIA Centaur at an estradiol concentration of 18 pg/mL (66 pmol/L), with the ARCHITECT i2000 assay in development and the Vitros ECi having a CV below 10% at this estradiol concentration. Agreement between the automated assays and ID-GC-MS was variable, with slopes ranging from 0.87 to 1.20. The Access, ARCHITECT i2000 in development, and the IMMULITE 2000 were the most accurate, with slopes of 0.99, 0.98, and 1.03, respectively. These findings indicate that the ARCHITECT i2000 estradiol assay in development had the best precision and accuracy of the assays evaluated for measurement of serum estradiol concentrations.

Estradiol↗
PubMed2004

Gadolinium magnetic resonance contrast agents produce analytic interference in multiple serum assays.

Gadolinium magnetic resonance contrast agents are known to interfere with some clinical chemistry tests, particularly colorimetric assays for serum calcium. We studied the effects of 4 agents, gadodiamide, gadoversetamide, gadopentetate dimeglumine, and gadoteridol, for interference with multiple serum assays. Gadodiamide and gadoversetamide produced clinically significant negative interference with colorimetric assays for serum angiotensin-converting enzyme, calcium, and zinc. These agents produced clinically significant positive interference in magnesium and total iron binding capacity assays and both positive and negative interference in iron assays. Gadopentetate dimeglumine produced a negative interference with iron assays, and gadopentetate dimeglumine and gadoteridol produced negative interference with a colorimetric zinc assay. Caution should be exercised when using colorimetric assays for angiotensin-converting enzyme, calcium, iron, magnesium, total iron binding capacity, and zinc in serum samples from patients who have recently received magnetic resonance contrast agents. In general, gadodiamide and gadoversetamide are more likely to produce a clinically significant interference than gadopentetate dimeglumine and gadoteridol. Likewise, certain analytic methods are more prone to interference, while others not affected.

Blood Chemical Analysis↗
PubMed2004

Association of obesity with inflammation in chronic kidney disease: a cross-sectional study.

OBJECTIVE: As adipose tissue releases inflammatory cytokines, obesity is associated with elevated C-reactive protein (CRP) levels in the general population. We examined the cross-sectional association of body mass index (BMI) with CRP in patients with chronic kidney disease (CKD). DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: Ninety-four CKD patients with varying levels of renal function seen at the University of Utah outpatient renal clinic were studied. METHODS: Data on demographics (age, gender, race), comorbidity (diabetes mellitus, hypertension, myocardial infarction/angina, cerebrovascular disease, peripheral vascular disease, and smoking) and anthropometry (height and weight) were obtained by patient interview and chart reviews. High-sensitivity CRP was measured by the N-latex assay on a BN II nephelometer. MAIN OUTCOME MEASURE: Risk factors of high CRP. RESULTS: In a multivariable logistic regression model, when compared with patients with a BMI < 25, the odds of CRP > 3.0 mg/L were 2.5-fold (95% CI, 1.02 to 5.99) higher in patients with BMI > or = 30. In a stepwise multiple linear regression model, BMI (regression coefficient [beta] = 0.06; 95% CI, 0.03 to 0.1; P < .01), serum creatinine (beta = 0.16; 95% CI, 0.04 to 0.3; P = .01) and age (beta = 0.01; 95% CI, -0.001 to 0.03; P = .05) were significantly associated with log transformed CRP. CONCLUSION: These data suggest that as in the general population, in CKD patients, obesity, a traditional risk factor for atherosclerosis, is associated with inflammation, a novel risk factor for atherosclerosis.

Adult↗
PubMed2003

Performance characteristics of the Dimension RxL iron and total iron-binding capacity methods.

BACKGROUND: Measurements of serum iron and total iron-binding capacity (TIBC) can be used to aid the diagnosis of iron deficiency and iron overload states. A variety of different methods for these measurements are commercially available. METHODS: Linearity, imprecision and hemoglobin interference of homogeneous iron and TIBC methods on a Dimension RxL analyzer were assessed. Method comparison studies were performed with a Vitros 950 analyzer. RESULTS: The Dimension RxL iron method was linear from 40 to 1000 microg/dl. The coefficient of variation of the iron and TIBC methods were <4% and <2%, respectively, at iron concentrations of 68 and 228 microg/dl and TIBC concentrations of 206 and 384 microg/dl. Comparison of the Vitros 950 and Dimension RxL iron methods gave a slope of 0.97, an intercept of 6.0 and r=0.99. Corresponding results for the TIBC methods were 1.02, -6.6 and r=0.97, respectively. Simulation of acute iron overload in vitro did not produce the same effect on TIBC measurements as in vivo overload. Iron recovery by the Dimension RxL method was reduced 40-60% by the addition of deferoxamine at a concentration of 200 micromol/l. CONCLUSIONS: The Dimension RxL assay provides acceptable measurements of iron and TIBC in routine patient samples. Iron measurements are unreliable in the presence of deferoxamine.

Anemia, Iron-Deficiency↗
PubMed2003

Analysis of transient-grating signals for reacting-flow applications.

Single-shot transient-grating measurements for thermometry in pressurized reacting flows are examined in the context of rapid digital signal processing. Simple approaches are discussed for temperature determination and rejection of unwanted signals in real-time measurement applications. Examples of temperature data in pressurized postflame gases are presented in the form of probability-density functions (PDFs). Three contributions to the PDF half-widths are discussed. Analysis of phase-matching requirements indicates that beam steering as a result of density fluctuations affects the signal amplitude but not the grating period. Therefore, such stochastic beam deviations have little effect on the derived temperatures. Mode noise on the cw probe beam as well as linear light scattering are found to be insignificant in the frequency range of the observed transient-grating acoustic signature. Use of a single-mode laser for the pump beams is shown to enhance the signal intensity.

Journal Article↗
PubMed2003

Residents from five training programs report improvements in knowledge, attitudes and skills after a rotation with a hospice program.

BACKGROUND: The faculty of the Center for Palliative Studies teach residents from 5 different primary care residency training programs who rotate at San Diego Hospice: 3 in Internal Medicine, 2 in Family Medicine. Residents participate in the care of patients in the inpatient care setting and make joint home visits with physicians and other team members. A series of 4 lectures on end-of-life care is given on Tuesday mornings: management of pain, other symptoms, interdisciplinary roles of chaplains, social workers, nurses, and grief/bereavement are discussed. In addition, there is a Tuesday noon conference that follows a journal club format. Because of scheduling, residents from some programs are not able to attend all lectures and conferences. METHODS: A 27-item self-assessment evaluation tool was developed for administration to residents before and after their experience. A total of 65 evaluations for residents rotating in academic year 1997-98 and 1998-1999 were collated and analyzed. RESULTS: When evaluated as a whole, residents noted significant improvements in their ability to assess and treat symptoms, to tell patient/family about the dying process and to care for dying patients at home (range in improvement from 26% to 67%, p < 0.05 using paired t-test). About half of the residents perceived that the content was not available elsewhere in their training. CONCLUSION: We conclude that a single hospice rotation can effectively contribute to resident education in multiple programs.

Attitude of Health Personnel↗
PubMed2003

Performance characteristics of four immunonephelometric assays for the quantitative determination of IgA and IgM in cerebrospinal fluid.

Measurement of IgA and IgM in cerebrospinal fluid (CSF) can be useful in the diagnosis of multiple sclerosis and other central nervous system disorders. The Dade Behring (Deerfield, IL) N Latex IgA and N Latex IgM tests on the BN II System and Beckman Coulter (Brea, CA) low-concentration IgA and IgM tests on the IMMAGE Immunochemistry System were evaluated for linearity, imprecision, method comparison, and reference interval verification. Both IgA methods were linear from 1.4 to at least 50 mg/L. Both IgM methods were linear from 0.14 to more than 6 mg/L. The total imprecision of the BN II IgA and IgM methods and the IMMAGE IgA method was less than 10%. The imprecision of the IMMAGE IgM method was 10.2% at 0.49 mg/L and less than 5% at higher IgM concentrations. Method comparison studies indicated that IgA and IgM methods on both instruments showed good comparability. Reference interval studies demonstrated that both methods had similar reference intervals that agreed with published values of less than 6 mg/L for IgA and less than 1.3 mg/L for IgM. Methods for quantifying IgA and IgM in CSF on the BN II and IMMAGE nephelometers perform well and give comparable results.

Humans↗
PubMed2003

Comparison of five automated serum and whole blood folate assays.

Serum and whole blood folate measurements are used to establish folate deficiency. Most methods used in clinical laboratories are automated, nonistopic methods that use folate-binding protein. Linearity, imprecision, and method comparison studies, including serum and whole blood hemolysates, were performed with the Access, Advia Centaur, ARCHITECT i2000, Elecsys 2010, and IMMULITE 2000 methods. The QuantaPhase II radioassay served as the comparison method. (Proprietary information is given in the text.) The Access and IMMULITE 2000 methods had higher systematic errors in linearity studies than the other 3 methods. The imprecision of all methods was acceptable (coefficient of variation, < 10%) even at low folate concentrations with the exception of the Elecsys 2010 (coefficient of variation, 16%). Method comparison studies using serum samples revealed calibration differences between the Access and Elecsys 2010 methods and the comparison method. Method comparison studies using whole blood samples showed poorer agreement between each of the automated methods and the comparison method than was seen with serum samples. The ARCHITECT i2000 folate assay demonstrated the best analytic performance. The poor agreement seen with whole blood hemolysates likely is due to calibration differences and differences in hemolysate preparation conditions.

Blood Chemical Analysis↗
PubMed2002

Performance characteristics of an automated high-sensitivity C-reactive protein assay on the Dimension RXL analyzer.

BACKGROUND: C-reactive protein (CRP) is a nonspecific marker of inflammation that can be used as a marker for atherosclerotic risk. This application requires increased precision at low CRP concentrations compared to traditional assays. METHODS: The Dimension RXL is an automated chemistry analyzer for central laboratory use. The limit of detection, limit of quantification, linearity and imprecision of a high-sensitivity CRP assay developed for it were assessed. Method comparison studies were performed using samples both inside and outside the reference interval. The presence of a prozone effect was also evaluated. RESULTS: The limit of detection was 0.7 mg/l. The method was linear from 2 to 60 mg/l and from 1 to 60 mg/l using systematic error limits of 10% and 20%, respectively. The total imprecision was <10% for CRP concentrations above 1.5 mg/l. No prozone effect was seen at a CRP concentration of 450 mg/l, the highest concentration tested. Using samples from 212 apparently healthy adults, the Dimension RXL method demonstrated good concordance with the BN II high-sensitivity CRP method for samples in the highest quartile. It also compared well using samples with elevated CRP concentrations. CONCLUSIONS: The Dimension RXL high-sensitivity CRP method may be adequate for atherosclerotic risk prediction in clinical practice if accurate and precise measurement is only required for the highest quartile. However, the total error of this method for CRP concentrations <3 mg/l appears too large for accurate assignment to lower risk groups.

Adult↗
PubMed2002

Performance characteristics of four immunoassays for antiepileptic drugs on the IMMULITE 2000 automated analyzer.

Carbamazepine, phenobarbital, phenytoin, and valproic acid are commonly used antiepileptic drugs that show complicated pharmacokinetic behavior Nonisotopic immunoassays are used routinely to monitor these drugs, and assay specificity is important to obtain accurate results. By using samples from subjects receiving each of these antiepileptic medications, competitive immunoassays for them were evaluated on an IMMULITE 2000 automated chemiluminescent analyzer (Diagnostic Products, Los Angeles, CA). Phenytoin assays were evaluated using an additional set of samples from patients with abnormal renal function. All 4 methods were linear, had imprecision of less than 10%, and compared well with other commercial immunoassays. A positive bias was observed for phenytoin measured in samples from uremic patients compared with a high-performance liquid chromatography reference method. The molar cross-reactivity of carbamazepine-10,11-epoxide was 12% in the carbamazepine assay. Phenytoin metabolites and fosphenytoin had substantial cross-reactivity in the phenytoin assay. All antiepileptic drug assays performed well and are suitable for use in monitoring patients receiving antiepileptic drug therapy. One possible exception is the phenytoin assay with samples from patients with renal insufficiency.

Anticonvulsants↗
PubMed2002

False-positive AxSYM cardiac troponin I results in a 53-year-old woman.

A number of classes of endogenous antibodies, including heterophile, rheumatoid factor, and autoantibodies, can interfere with immunoassay measurements of many different analytes. Heterophile and rheumatoid factor antibody interferences have been described previously for the AxSYM cardiac troponin I assay. Several commercial products have been developed to neutralize heterophile antibody interferences. We describe a patient with multiple apparently falsely elevated cardiac troponin I results that were unique to the AxSYM analyzer. These cardiac troponin I results diluted linearly. When treated with 2 different heterophile-blocking reagents, the magnitudes of the falsely elevated results increased 17- and 26-fold, and these results also demonstrated dilution linearity. This interfering substance could be removed by passage through an immobilized protein A column and by polyethylene glycol precipitation. It does not appear to be a classic heterophile antibody, nor is it a paraprotein. Laboratorians must remain constantly vigilant for immunoassay interferences that lead to clinically significant inaccurate results and must recognize that accepted methods for detecting and neutralizing the interference may be ineffective.

False Positive Reactions↗
PubMed2002

Analysis of catecholamines in urine by positive-ion electrospray tandem mass spectrometry.

BACKGROUND: Determination of urinary catecholamines (CATs) is considered important for clinical diagnosis of pheochromocytoma, paraganglioma, and neuroblastoma. The major disadvantages of existing tests include relatively long instrumental analysis time and potential interference from drugs and drug metabolites that are structurally similar to CATs. METHODS: CATs were extracted from a 300-microL aliquot of urine by a two-step liquid-liquid extraction method specific for compounds containing a catechol group. Chromatographic separation did not require the use of ion-pairing reagents, which typically hinder MS detection but are frequently used in HPLC analysis of CATs. Instrumental analysis was performed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in the multiple-reaction monitoring mode. Stable-isotope-labeled CATs were used as internal standards. RESULTS: Epinephrine (E), norepinephrine (NE), and dopamine (D) were measured within 3.5 min instrumental run time. Quantification limits were 2.5 microg/L for E and D and 10 microg/L for NE. The total imprecision (CV) was < or =9.6%; extraction recoveries were 71% +/- 12%. CONCLUSIONS: HPLC with ESI-MS/MS in combination with sample preparation specific to catechol group-containing compounds allows rapid testing for disorders associated with increased CAT concentrations. The method is free of interferences from drugs and drug metabolites, which commonly interfere with HPLC methods.

Catecholamines↗
PubMed2002

Rapid analysis of metanephrine and normetanephrine in urine by gas chromatography-mass spectrometry.

BACKGROUND: Widely used HPLC methods for quantification of metanephrine and normetanephrine in urine often have long analysis times and are frequently plagued by drug interferences. We describe a gas chromatography-mass spectrometry method designed to overcome these limitations. METHODS: Metanephrine and normetanephrine conjugates were converted to unconjugated metanephrine and normetanephrine by acid hydrolysis. To avoid the rapid decomposition of the deuterated internal standards (metanephrine-d(3) and normetanephrine-d(3)) under hydrolysis conditions, the internal standards were added after hydrolysis. Solid-phase extraction was used to isolate the hydrolyzed metanephrines from urine. Samples were concentrated by evaporation, then derivatized simultaneously with N-methyl-N-(trimethylsilyl)trifluoroacetamide and N-methyl-bis-heptafluoro-butryamide at room temperature. RESULTS: The assay was linear from 25 to 7000 microg/L. The intraassay CVs were < 5 % and the interassay CVs < 12%. Comparison with a routine HPLC method (n = 192) by Deming regression yielded a slope of 1.00 +/- 0.02 microg/L, an intercept of -5.8 +/- 7.8 micro/L, and S(y/x) = 50.6 microg/L for metanephrine and a slope of 0.94 +/- 0.03, intercept of 19 +/- 11 microg/L, and S(y/x) = 60 microg/L for normetanephrine. The correlation coefficients (r) were calculated after log transformation of the data and gave r = 0.97 for metanephrine and r = 0.97 for normetanephrine. Interference from common medications or drug metabolites was seen in <1% of samples. The time between sequential injections was < 7 min. CONCLUSIONS: This new gas chromatography-mass spectrometry assay for total fractionated metanephrines is rapid, compares well with a standard HPLC assay, and avoids most drug interferences that commonly affect HPLC assays for urine metanephrines.

Biomarkers, Tumor↗