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Clinical Chemistry, Vol 42, 146-154, Copyright © 1996 by American Association for Clinical Chemistry
JC Nelson and RB Wilcox
Loma Linda University School of Medicine, CA 92354, USA.
Excessive bias and imprecision are major analytical problems associated with some assays for free and total thyroxine (T4). Bias in free T4 methods is largely proportional to variations in serum T4 binding. In direct methods, this is attributable to requirements for substantial quantities of protein-bound T4 to replace analytical losses of free T4. In some total T4 methods, bias is inversely proportional to the amount of serum T4 binding and is attributable to the incomplete release of serum protein-bound T4. In others, bias is fixed and attributable to inaccurate calibration. Manufacturers should report the bias in their methods. Calibrations should be standardized. Imprecision varies widely among methods, but is generally less for total T4 methods than for free T4 methods. A consensus on quantitative analytical performance goals for free and total T4 methods would be helpful. Here, performance goals are proposed, based in part on the best achievements of current methods.
The following articles in journals at HighWire Press have cited this article:
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  J. E.M. Midgley and N. D. Christofides Point: Legitimate and Illegitimate Tests of Free-Analyte Assay Function Clin. Chem., March 1, 2009; 55(3): 439 - 441. [Full Text] [PDF]
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R. B. Wilcox and J. C. Nelson Counterpoint: Legitimate and Illegitimate Tests of Free-Analyte Assay Function: We Need to Identify the Factors That Influence Free-Analyte Assay Results Clin. Chem., March 1, 2009; 55(3): 442 - 444. [Full Text] [PDF]
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L. M. Thienpont A Major Step Forward in the Routine Measurement of Serum Free Thyroid Hormones Clin. Chem., April 1, 2008; 54(4): 625 - 626. [Full Text] [PDF]
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K. Van Uytfanghe, D. Stockl, H A. Ross, and L. M. Thienpont Use of Frozen Sera for FT4 Standardization: Investigation by Equilibrium Dialysis Combined with Isotope Dilution-Mass Spectrometry and Immunoassay Clin. Chem., September 1, 2006; 52(9): 1817 - 1821. [Abstract] [Full Text] [PDF]
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S. S. Holm, L. Andreasen, S. H. Hansen, J. Faber, and P. Staun-Olsen Influence of Adsorption and Deproteination on Potential Free Thyroxine Reference Methods Clin. Chem., January 1, 2002; 48(1): 108 - 114. [Abstract] [Full Text] [PDF]
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J. E.M. Midgley Direct and Indirect Free Thyroxine Assay Methods: Theory and Practice Clin. Chem., August 1, 2001; 47(8): 1353 - 1363. [Abstract] [Full Text] [PDF]
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R. Sapin, J.-L. Schlienger, F. Gasser, E. Noel, B. Lioure, F. Grunenberger, B. Goichot, and D. Grucker Intermethod Discordant Free Thyroxine Measurements in Bone Marrow-transplanted Patients Clin. Chem., March 1, 2000; 46(3): 418 - 422. [Full Text] [PDF]
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N. D. Christofides, E. Wilkinson, M. Stoddart, D. C. Ray, and G. J. Beckett Assessment of Serum Thyroxine Binding Capacity-dependent Biases in Free Thyroxine Assays Clin. Chem., April 1, 1999; 45(4): 520 - 525. [Abstract] [Full Text] [PDF]
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S. Saw, S. Sethi, and T.-C. Aw Technical Evaluation of Thyroid Assays on the Vitros ECi Clin. Chem., April 1, 1999; 45(4): 578 - 580. [Full Text] [PDF]
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N. Despres and A. M. Grant Antibody interference in thyroid assays: a potential for clinical misinformation Clin. Chem., March 1, 1998; 44(3): 440 - 454. [Abstract] [Full Text] [PDF]
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A. G. W. Norden, R. A. Jackson, L. E. Norden, A. J. Griffin, M. A. Barnes, and J. A. Little Misleading results from immunoassays of serum free thyroxine in the presence of rheumatoid factor Clin. Chem., June 1, 1997; 43(6): 957 - 962. [Abstract] [Full Text] [PDF]
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