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Biomedical subjects

Richard F Roberts

Publications and source records attributed to Richard F Roberts.

6 recordsLinked to original sources
PubMed2006

Performance characteristics of seven automated thyroxine and T-uptake methods.

BACKGROUND: Estimates of the free thyroxine concentration can be made using measurements of thyroxine (T4) and the thyroid hormone binding ratio (THBR, usually reported as T-uptake) according to the formula free thyroxine index (FTI)=T4xTHBR. We evaluated the performance characteristics of 7 pairs of automated T4 and T-uptake methods. METHODS: We evaluated the Architect i2000, AxSYM, ADVIA Centaur, UniCel DxI 800, Immulite 2000, Modular E170 and Vitros ECi methods for T4 and T-uptake. Imprecision was assessed by duplicate determinations on 3 levels of quality control material per run, 2 runs per day, on 5 separate days. Method comparison studies were performed with 205 patient samples and 68 samples from subjects in the second or third trimester of pregnancy. Results for both imprecision and method comparison were converted to the THBR as outlined by each method's manufacturer. RESULTS: Overall CVs for T4 and THBR methods were 3.2-8.9% and 1.2-6.7%, respectively. T4 methods generally agreed well. The THBR methods did not agree nearly as well. Comparison of FTI results with free T4 by equilibrium dialysis showed good correlation but different slopes. CONCLUSIONS: All methods show adequate precision but the THBR and FTI results are not well standardized.

Thyroxine↗
PubMed2005

Comparison of differing C-reactive protein assay methods and their impact on cardiovascular risk assessment.

A medium-sensitivity assay for C-reactive protein (CRP) was compared with a high-sensitivity, enhanced immunoturbidimetric assay in 803 angiographically studied patients. Different absolute CRP values were found by the assays, but there was a high correlation by quartile rank and similar predictive values for death and myocardial infarction. This suggests that the conclusions of previous studies performed using the medium-sensitivity assay are still valid but that cross-study comparisons should use percentile rank.

Blood Chemical Analysis↗
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

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↗