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Letters |
1 Service de Biochimie, CHUQ-Hôtel-Dieu de Québec, 11 Côte du Palais, Quebec, G1R 1P5 Canada
2 Service de Biochimie, Hôtel-Dieu de Lévis, 143 rue Wolfe, Quebec, G6V 3Z1 Canada
aAddress correspondence to this author at: Service de Biochimie, CHUQ-Hôtel-Dieu de Québec, 11 Côte du Palais, Quebec, G1R 1P5 Canada. Fax 418-691-5709; e-mail pierre.douville{at}bcx.ulaval.ca.
To the Editor:
We report here the observation of a falsely decreased HDL-cholesterol (HDL-C) result obtained with the Roche HDL-C Plus assay (polyethylene glycol-modified enzymes, sulfated 
-cyclodextrin, and dextran sulfate; cat no. 1930648) in an asymptomatic 78-year-old woman (1). The total cholesterol of the patient was 3.2 mmol/L, the triglycerides were 1.3 mmol/L, and the HDL-C was suppressed (<0) on a Roche Modular analyzer. The same analysis was repeated on the Johnson & Johnson Vitros (with magnetic separation of particles; cat. no. 1042523) and the Beckman LX-20 (with a polyanion-polymer/detergent reagent; cat. no. 650207) analyzers. The HDL-C concentrations according to these methods were 1.2 and 1.0 mmol/L, respectively. On the Roche analyzer, the absorbance of the blank was higher than the final absorbance result, giving a negative value by subtraction. Lipoprotein electrophoresis revealed a normal band.
We therefore suspected the presence of a paraprotein that would precipitate with the first reagent, possibly related to dextran. Serum total proteins and albumin were 101 and 40 g/L, respectively. Serum protein electrophoresis revealed a monoclonal band in the 
region that was unknown to the treating physician. This monoclonal band was characterized by immunofixation as an IgM-
band that was estimated at 30 g /L.
We selected other sera from patients known to have a monoclonal band and assayed these sera for HDL-C with two different assays: the Roche HDL-C Plus assay and a precipitation method using heparin-manganese (Table 1
).
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The interference was identified by visual inspection of the absorbance graphs and confirmed with the precipitation method. We identified other cases of falsely decreased results in some samples, independent of the concentration or type of paraprotein involved (Table 1
). The exact incidence of this bias was not known, but it was possibly not uncommon because we found several cases in a small series of patients.
Such interference does not always lead to suppression of a HDL-C result because it could simply lower the result. This decrease would go unnoticed with the current Roche application. In our view, some modifications could be introduced to screen for this phenomenon. This interference by monoclonal bands with the HDL-C direct assay is not reported in the 1997 edition of Effects of Disease on Clinical Laboratory Tests by Friedman and Young (2) or in the manufacturer’s package insert, except for the following statement: "In rare cases, increased immunoglobulin concentrations can lead to falsely increased HDL-cholesterol results". There is no mention of falsely decreased results in patients with paraproteins. Because the prevalence of paraproteins in the population is significant, it is conceivable that some patients with benign paraproteins may have a falsely decreased HDL-C result that could alter their cardiovascular risk estimates and treatment by physicians.
References
The following articles in journals at HighWire Press have cited this article:
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  J. P. Bida, R. A. Kyle, T. M. Therneau, L. J. Melton III, M. F. Plevak, D. R. Larson, A. Dispenzieri, J. A. Katzmann, and S. V. Rajkumar Disease Associations With Monoclonal Gammopathy of Undetermined Significance: A Population-Based Study of 17,398 Patients Mayo Clin. Proc., August 1, 2009; 84(8): 685 - 693. [Abstract] [Full Text] [PDF]
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 B. I. Dalal and M. L. Brigden Factitious Biochemical Measurements Resulting From Hematologic Conditions Am J Clin Pathol, February 1, 2009; 131(2): 195 - 204. [Abstract] [Full Text] [PDF]
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 A. Smogorzewska, J. G. Flood, W. H. Long, and A. S. Dighe Paraprotein Interference in Automated Chemistry Analyzers Clin. Chem., September 1, 2004; 50(9): 1691 - 1693. [Full Text] [PDF]
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A. Baca, R. J. Haber, K. Sujishi, P. H. Frost, and V. L. Ng Artifactual Undetectable HDL-Cholesterol with the Beckman Synchron LX and Vitros 950 Assays Temporally Associated with a Paraprotein Clin. Chem., January 1, 2004; 50(1): 255 - 256. [Full Text] [PDF]
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