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A 67-year-old woman with a systemic inflammatory syndrome and sicca.

Case Description

A 67-year-old woman presented with dry eyes, dry mouth, intermittent polyarticular nonerosive arthropathy, bronchial and bronchiolar involvement with bronchiectasis, peripheral sensory neuropathy, cryoglobulinemic vasculitis (IgM [kappa] paraprotein), pronounced hypergammaglobulinemia ([gamma]- globulin fraction, 28.6 g/L; reference interval, 8.0-13.5 g/L), and rheumatoid factor positivity (rheumatoid arthritis latex test, 728 IU/mL; reference interval, [less than or equal to] 40 IU/mL). Both parotid glands were enlarged, especially on the left side (Fig. 1). Puncture of a parotid cyst revealed benign material suggestive of a sialocoele (salivary cyst). The results of antinuclear antibody testing were negative (indirect immunofluorescence, screening dilution 1:40).



1. What is the most likely diagnosis?

2. Which result is inconsistent with the clinical picture?

3. What could be done to investigate the inconsistent results?


The clinical scenario strongly suggested primary Sjogren syndrome with multiorgan involvement. The negative result in the antinuclear antibody testing argued against Sjogren syndrome, however. Because the negative result did not match with the clinical presentation, further serial dilutions were performed, and a positive fluorescence signal was obtained with diluted serum samples. A fine speckled pattern was observed at serum dilutions of 1:80, 1:160, and 1:320, which pointed to the prozone (hook) effect as the cause of the false-negative result. The prozone effect is the phenomenon of a false-negative (low) result in the presence of a high concentration of the analyte (1). The mechanism of the prozone effect relates to the optimal ratio of antigen to antibody. Further identification of the antibodies revealed anti-SSA antibodies, a finding consistent with the diagnosis of Sjogren syndrome. Only a few cases of the prozone phenomenon for anti-nuclear antibody detection have been described. McGuiness et al. reported the prozone phenomenon for the antinuclear antibody assay in a case of druginduced lupus (2).

Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.

Authors' Disclosures of Potential Conflicts of Interest: No authors declared any potential conflicts of interest.

Role of Sponsor: The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, or preparation or approval of manuscript.

Acknowledgments: We are grateful to Godelieve Godefridis and Jacqueline L'heureux for expert technical assistance.


(1). Remaley AT, Hortin GL. Protein analysis for diagnostic applications. In: Detrick B, Hamilton RG, Folds JD, eds. Manual of molecular and clinical laboratory immunology. 7th ed. Washington (DC): ASM Press; 2006. p 7-21.

(2). McGuiness M, Frye RA, Deng JS. Atenelol-induced lupus erythematosus. J Am Acad Dermatol 1997;37:298-9.

Xavier Bossuyt, [1] * Godelieve Marien, [1] and Steven Vanderschueren [2]

[1] Laboratory Medicine, Immunology, University Hospitals Leuven, Leuven, Belgium;

[2] General Internal Medicine, University Hospitals Leuven, Leuven, Belgium.

* Address correspondence to this author at: Xavier Bossuyt, Laboratory Medicine, Immunology, University Hospitals Leuven, Herestraat 49, B-3000 Leuven, Belgium. Fax 32-13-347042; e-mail

DOI: 10.1373/clinchem.2010.150789
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Title Annotation:the Clinical Chemist: What is Your Guess
Author:Bossuyt, Xavier; Marien, Godelieve; Vanderschueren, Steven
Publication:Clinical Chemistry
Date:Sep 1, 2010
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