Comparing the power of quality-control rules to detect persistent systematic error.
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A simulation approach that allows direct estimation of the power of a quality-control rule to detect error that persists until detection is used to compare and evaluate the error detection capabilities of a group of quality-control rules. Two persistent error situations are considered: a constant shift and a linear trend in the quality-control mean. A recently proposed "moving slope" quality-control test for the detection of linear trends is shown to have poor error detection characteristics. A multimean quality-control rule is introduced to illustrate the strategy underlying multirule procedures, which is to increase power without sacrificing response rate. This strategy is shown to provide superior error detection capability when compared with other rules evaluated under both error situations. (+info)
Comparing the power of quality-control rules to detect persistent increases in random error.
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This paper continues an investigation into the merits of an alternative approach to the statistical evaluation of quality-control rules. In this report, computer simulation is used to evaluate and compare quality-control rules designed to detect increases in within-run or between-run imprecision. When out-of-control conditions are evaluated in terms of their impact on total analytical imprecision, the error detection ability of a rule depends on the relative magnitudes of the between-run and within-run error components under stable operating conditions. A recently proposed rule based on the F-test, designed to detect increases in between-run imprecision, is shown to have relatively poor performance characteristics. Additionally, several issues are examined that have been difficult to address with the traditional evaluation approach. (+info)
Medical devices; clinical chemistry and clinical toxicology devices; classification of newborn screening test systems for amino acids, free carnitine, and acylcarnitines using tandem mass spectrometry. Final rule.
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The Food and Drug Administration (FDA) is classifying newborn screening test systems for amino acids, free carnitine, and acylcarnitines using tandem mass spectrometry into class II (special controls). The special control that will apply to the device is the guidance document entitled "Class II Special Controls Guidance Document: Newborn Screening Test Systems for Amino Acids, Free Carnitine, and Acylcarnitines Using Tandem Mass Spectrometry." The agency is taking this action in response to a petition submitted under the Federal Food, Drug, and Cosmetic Act (the act) as amended by the Medical Device Amendments of 1976, the Safe Medical Devices Act of 1990, the Food and Drug Administration Modernization Act of 1997, and the Medical Device User Fee and Modernization Act of 2002. The agency is classifying the device into class II (special controls) in order to provide a reasonable assurance of safety and effectiveness of the device. Elsewhere in this issue of the Federal Register, FDA is publishing a notice of availability of a guidance document that is the special control for this device. (+info)
Clinical chemistry through Clinical Chemistry: a journal timeline.
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The establishment of the modern discipline of clinical chemistry was concurrent with the foundation of the journal Clinical Chemistry and that of the American Association for Clinical Chemistry in the late 1940s and early 1950s. To mark the 50th volume of this Journal, I chronicle and highlight scientific milestones, and those within the discipline, as documented in the pages of Clinical Chemistry. Amazing progress has been made in the field of laboratory diagnostics over these five decades, in many cases paralleling-as well as being bolstered by-the rapid pace in the development of computer technologies. Specific areas of laboratory medicine particularly well represented in Clinical Chemistry include lipids, endocrinology, protein markers, quality of laboratory measurements, molecular diagnostics, and general advances in methodology and instrumentation. (+info)
High reproducibility of serum anti-Mullerian hormone measurements suggests a multi-staged follicular secretion and strengthens its role in the assessment of ovarian follicular status.
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BACKGROUND: Our aim was to compare the intercycle reproducibility of serum anti-Mullerian hormone (AMH) measurements with that of other markers of ovarian follicular status. METHODS: Forty-seven normo-ovulatory, infertile women underwent serum AMH, inhibin B, estradiol and FSH measurements and early antral follicle (2-12 mm in diameter) counts by transvaginal ultrasound on cycle day 3 during three consecutive menstrual cycles. Reproducibility of measurements was estimated using intra-class correlation coefficient (ICC) calculation. We also assessed the number of replicate measurements theoretically needed to reach satisfactory reliability of results. RESULTS: Serum AMH showed significantly higher reproducibility (ICC, 0.89; 95% confidence interval, 0.83-0.94) than inhibin B (0.76; 0.66-0.86; P < 0.03), estradiol (0.22; 0.03-0.41; P < 0.0001) and FSH levels (0.55; 0.39-0.71; P < 0.01), and early antral follicle counts (0.73; 0.62-0.84; P < 0.001), and reached satisfactory reliability with a single measurement. CONCLUSIONS: The improved cycle-to-cycle consistency of AMH as compared with other markers of ovarian follicular status is in keeping with its peculiar production by follicles at several developmental stages and further supports its role as a cost-effective, reliable marker of ovarian fertility potential. (+info)
Are clinical laboratory proficiency tests as good as they can be?
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Present proficiency test services that use the peer group mean and statistically derived ranges of acceptability are not serving us optimally and are even counterproductive in some respects. We recommend that the target value be determined by a widely accepted reference method and that acceptable ranges be based on criteria related to clinical need. This approach was adopted several years ago in Germany and has already eliminated the use of several unsatisfactory analytical methods. Because the transition would probably take many years, we propose an interim solution to allow instrument manufacturers and laboratorians to adapt to these changes. The current peer group means and acceptable ranges should be supplemented by reference method values and acceptable ranges, based on clinical need, so that manufacturers and laboratorians can judge their performance against these new criteria and make the necessary adjustment in instrumentation and methodology. These processes should be paralleled by efforts to produce proficiency test materials that will not exhibit the matrix problems of present-day preparations. (+info)
Performance characteristics of four automated natriuretic peptide assays.
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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. (+info)
Analytical relationships among Biosite, Bayer, and Roche methods for BNP and NT-proBNP.
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This study determined whether, for patient monitoring, it is feasible to convert B-type natriuretic peptide (BNP) results obtained using Triage (BNP, Biosite, San Diego, CA), Centaur (BNP, Bayer Diagnostics, Tarrytown, NY), and Elecsys 2010 (N-terminal proBNP; Roche, Indianapolis, IN) assays. Concordance between assays and effects of renal impairment also were assessed. Samples were primarily from emergency center patients. Biosite testing was performed immediately; Bayer and Roche testing was performed later on plasma stored frozen (-30 degrees C). Logistic regression relationships were as follows: Bayer = 0.57 Biosite + 23.1, n = 121, R2 = 0.85; Roche = 6.09 Biosite -220.4 + 1,131.6 (if female), n = 131, R2 = 0.57; and Roche = 15.34 Bayer + 2,400.8, n = 150, R2 = 0.23. An increased serum creatinine level (>/=2 mg/dL [>/=177 micromol/L]) influenced the Roche results. We conclude the following from this preliminary study: (1) Results from one method cannot be converted reliably to another using regression relationships. (2) When using manufacturers'cutoff values, concordance between assays was acceptable. (3) Renal impairment affected Roche results. (+info)