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1 Professor of Clinical Biochemistry, Emeritus, University of Surrey, Guildford GU2 7XH, United Kingdom.
Address for correspondence: Oriel House, Derby Road, Haslemere GU27 1BP, United Kingdom. Fax 44-1428-652-893; e-mail vincentmarks{at}bigfoot.com.
Background: Analytical interference in immunoassays can produce serious errors, but it is generally considered rare with modern analytical systems.
Method: Blood was collected from 10 donors with illnesses known to be associated with rheumatoid factor. Immunoassays for 74 analytes were performed in 66 clinical laboratories. Each sample was measured in duplicate, and again in duplicate after the addition of a proprietary heterophil blocking reagent, with the laboratory’s routinely used reagents and equipment. Reagents were typically supplied by the manufacturers of the closed analytical systems. Both competitive and sandwich immunoassays were investigated.
Results: Overall 
8.7% of the 3445 results were considered to be "false positive", many of them seriously so. Twenty-one percent of the erroneously high results (1.8% of all results) were potentially misleading and were corrected by blocking reagent, although 49% of such seriously high results (4.2% of all results) were not. A further 39% of the false-positive results (2.6% of all results) would not necessarily have appeared likely to produce adverse clinical consequences but were substantially lowered by the addition of the blocking reagent.
Conclusions: Random errors can occur with all types of immunoassays tested and can be difficult to identify even when repeated in another laboratory. Clinicians need to be aware of these limitations.
The following articles in journals at HighWire Press have cited this article:
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  P. Carraro and M. Plebani Errors in a Stat Laboratory: Types and Frequencies 10 Years Later Clin. Chem., July 1, 2007; 53(7): 1338 - 1342. [Abstract] [Full Text] [PDF]
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 V. Marks Hypoglycaemia: insulin and conflicts with the law The British Journal of Diabetes & Vascular Disease, November 1, 2006; 6(6): 281 - 285. [Abstract] [PDF]
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 T. W. Wallace, S. M. Abdullah, M. H. Drazner, S. R. Das, A. Khera, D. K. McGuire, F. Wians, M. S. Sabatine, D. A. Morrow, and J. A. de Lemos Prevalence and Determinants of Troponin T Elevation in the General Population Circulation, April 25, 2006; 113(16): 1958 - 1965. [Abstract] [Full Text] [PDF]
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J. D. Newman, P. B. Bergman, J. C.G. Doery, and N. D.H. Balazs Factitious increase in thyrotropin in a neonate caused by a maternally transmitted interfering substance. Clin. Chem., March 1, 2006; 52(3): 541 - 542. [Full Text] [PDF]
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L. J. Kricka and J. Y. Park Additive-Aggravated Assays: An Authoritative Answer Clin. Chem., October 1, 2005; 51(10): 1767 - 1767. [Full Text] [PDF]
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M. L. Cawood, H. P. Field, C. G. Ford, S. Gillingwater, A. Kicman, D. Cowan, and J. H. Barth Testosterone Measurement by Isotope-Dilution Liquid Chromatography-Tandem Mass Spectrometry: Validation of a Method for Routine Clinical Practice Clin. Chem., August 1, 2005; 51(8): 1472 - 1479. [Abstract] [Full Text] [PDF]
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M. Y. Liu, A. M. Xydakis, R. C. Hoogeveen, P. H. Jones, E. O. Smith, K. W. Nelson, and C. M. Ballantyne Multiplexed Analysis of Biomarkers Related to Obesity and the Metabolic Syndrome in Human Plasma, Using the Luminex-100 System Clin. Chem., July 1, 2005; 51(7): 1102 - 1109. [Abstract] [Full Text] [PDF]
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W. W.L. Choi, S. Srivatsa, and J. C. Ritchie Aberrant Thyroid Testing Results in a Clinically Euthyroid Patient Who Had Received a Tumor Vaccine Clin. Chem., March 1, 2005; 51(3): 673 - 675. [Full Text] [PDF]
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A. A.A. Ismail A Radical Approach Is Needed to Eliminate Interference from Endogenous Antibodies in Immunoassays Clin. Chem., January 1, 2005; 51(1): 25 - 26. [Full Text] [PDF]
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R. Sapin, A. Agin, and F. Gasser Misleading High Thyrotropin Results Obtained with a Two-Site Immunometric Assay Involving a Chimeric Antibody Clin. Chem., May 1, 2004; 50(5): 946 - 948. [Full Text] [PDF]
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P. A. Torjesen, L. Sandnes, and P. Boudou Serum Testosterone in Women as Measured by an Automated Immunoassay and a RIA * Dr. Boudou responds for the authors of the article cited above: Clin. Chem., March 1, 2004; 50(3): 678 - 679. [Full Text] [PDF]
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J. Kristiansen The Guide to Expression of Uncertainty in Measurement Approach for Estimating Uncertainty: An Appraisal Clin. Chem., November 1, 2003; 49(11): 1822 - 1829. [Abstract] [Full Text]
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L. L. Leape Striving for Perfection Clin. Chem., November 1, 2002; 48(11): 1871 - 1872. [Full Text] [PDF]
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