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Sialometry and sialochemistry: a non-invasive approach for diagnosing Sjögren's syndrome

W W I Kalk¹, A Vissink¹, B Stegenga¹, H Bootsma², A V Nieuw Amerongen³, C G M Kallenberg⁴

¹ Department of Oral and Maxillofacial Surgery, University Hospital Groningen, PO Box 30.001, 9700 RB Groningen, The Netherlands
² Department of Internal Medicine, Division of Rheumatology, University Hospital Groningen
³ Department of Oral Biology, Section of Oral Biochemistry, Faculty of Dentistry Amsterdam, The Netherlands
⁴ Department of Internal Medicine, Division of Clinical Immunology, University Hospital Groningen

Correspondence to:
Correspondence to:
Dr W W I Kalk, Department of Oral and Maxillofacial Surgery, University Hospital Groningen, PO Box 30.001, 9700 RB Groningen, The Netherlands;
w.w.i.kalk{at}kchir.azg.nl

Background: Analysis of salivary variables has frequently been proposed as a diagnostic tool for Sjögren's syndrome (SS). Because univocal salivary reference values are lacking, it is currently rather difficult to use sialometry and sialochemistry for diagnosing SS unless major changes have occurred in salivary secretion and composition.

Objective: To define reference values of several salivary variables, which offer a possible new and non-invasive means of diagnosing SS.

Methods: Cut off points were selected from receiver operating characteristic curves of gland-specific sialometrical and sialochemical variables, which have proved to be potentially relevant for diagnosing SS in a previous study—that is, sodium, chloride, and phosphate concentration in stimulated parotid and submandibular/sublingual (SM/SL) saliva, unstimulated and stimulated SM/SL flow rates, and lag phase of parotid secretion, respectively. By combining the most discriminating variables, two different diagnostic approaches for SS were applied in a group of 100 patients and subsequently evaluated in a second group of 20 patients. The first approach was to combine variables by applying their cut off points into sets of criteria for a positive diagnosis of SS. The second approach was to construct a logistic regression model that predicts the true state of a patient (SS or non-SS). From both approaches, the tests with highest likelihood ratio combined with the smallest number of rejected cases were selected for clinical use.

Results: The most accurate test combined the stimulated SM/SL flow rate and parotid sodium and chloride concentration as salivary variables for diagnosing SS; it had a sensitivity of 0.85 and a specificity of 0.96. The selected tests proved equally accurate in the second group of patients.

Conclusions: Because the proposed non-invasive diagnostic tools can be easily applied, do not need a laboratory other than for routine blood testing, and are very accurate, gland-specific sialometry and sialochemistry may eventually replace other, more invasive, diagnostic techniques for diagnosing SS.

Keywords: sialochemistry; sialometry; Sjögren's syndrome; diagnosis

Abbreviations: ROC, receiver operating characteristic; SM/SL, submandibular/sublingual; SS, Sjögren's syndrome

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