25.1Introduction

Sjögren’s syndrome (SS) is a systemic autoimmune disease that presents with sicca symptomatology of the main mucosa surfaces. The spectrum of the disease extends from sicca syndrome to systemic involvement (extraglandular manifestations) and may be complicated by the development of lymphoma. Patients with SS may present with a broad spectrum of autoantibodies and laboratory abnormalities. Most of the laboratory abnormalities have been described more frequently in patients with positive immunological markers. Some may be the first manifestation of primary SS, while others have no clinical significance. The most frequent cytopenias are normocytic anemia, leukopenia, and thrombocytopenia, which are all found more frequently in patients with positive immunological markers. Cytopenias are usually asymptomatic, but may be clinically overt in some cases. Erythrocyte sedimentation rates (ESRs) correlate closely with the percentage of circulating gammaglobulins (hypergammaglobulinemia) – frequently elevated in primary SS – but serum C-reactive protein concentrations are usually normal. Laboratory studies are a simple, useful, and noninvasive tool that can help identify subsets of patients with a high risk of developing of systemic manifestations and lymphoma.

25.2Serum Proteins

25.2.1Acute Phase Reactants

The erythrocyte sedimentation rate (ESR) is a common, nonspecific hematological test that indirectly measures systemic inflammation. In primary SS, nearly 25% of patients have an ESR >50 mm/h [1]. Patients with elevated ESRs have a high prevalence of extraglandular involvement [1] and other laboratory abnormalities such as anemia [1], anti-Ro/SS-A and –La/SS-B autoantibodies [1, 2], and rheumatoid factor (RF) [1]. A close relationship has also been found between ESR values and the percentage of serum gammaglobulins. ESR measurement is a useful hematologic marker in primary SS that seems to be related to B-cell polyclonal hyperactivity and the amount of circulating autoantibodies.

In contrast to the ESR, the C-reactive protein (CRP) has relatively little clinical significance in primary SS. Although 22% of patients with primary SS have mini- mal-to-moderate increases in CRP [3] levels, these patients do not differ clinically from those with normal CRP levels. In addition, no significant differences in CRP levels have been found in primary SS patients grouped according to the immunological profile (e.g., positivity or negativity for anti-Ro/SS-A and anti-La/SS-B autoantibodies) [2]. Higher CRP levels have been found in patients with associated SS [4]. Testing CRP levels in patients with primary SS may be most useful in the differential diagnosis between infection and systemic involvement.