Saliva analysis for monitoring dialysis and renal function.

Measurement of biological markers that demonstrate distinguishable and regular changes from preto postdialysis states can enable necessary monitoring of dialysis efficacy and the level of renal function in patients with end-stage renal disease. In a report in this issue of Clinical Chemistry, Blicharz et al. (1 ) suggest that the measurement of biomarkers in saliva may be an effective alternative method for monitoring the effectiveness of hemodialysis. In particular, Blicharz et al. highlight as markers of interest 2 small molecules present in saliva, nitrite and uric acid (UA). Monitoring of markers in saliva instead of serum is advantageous because saliva collection is a noninvasive, simple, and inexpensive approach with minimal infectious risk that can be performed by the patient with no need for involvement from medical personnel. Saliva can be tested at home, thus saving the need for a visit to the clinic or hospital. Markers for monitoring patients with end-stage renal disease must fulfill 3 requirements: (a) the markers should properly reflect serum concentrations of toxins to be dialyzed, (b) the correlation between the serum and saliva concentrations of the markers should be as high as possible, and (c) the concentrations of the markers in saliva should not be altered by intraoral conditions or by processes associated with marker transport from serum into saliva. Whole saliva is composed of components that originate in the major and minor salivary glands as well as from nonsalivary glandular sources, and the composition of saliva may vary under resting vs stimulated conditions (2 ). More than 90% of saliva is secreted by the major salivary glands, which include the parotid, submandibular, and sublingual glands, whereas only a small portion of saliva originates in minor salivary glands and intraoral sources such as oral mucosa or gingiva. Contribution to the saliva from gastrointestinal reflux is minute and of negligible importance under normal conditions. Various components of saliva are either passively diffused or actively transported directly from the serum into the saliva through the oral mucosa and/or gingiva. The composition of such components in saliva may or may not reflect their serum composition (3–5 ). The watery component and the electrolytes in saliva are derived from serum, but the various immunoglobulins, enzymes, and proteins may originate in the serum, the salivary glands, or other intraoral and extraoral sites. Analysis of saliva composition may be used as a diagnostic tool for the localization and assessment of various systemic diseases (such as end-stage renal disease). Such analysis must be based on a broad understanding of the specific concentrations and origins of the various immunological and biochemical components of saliva (6, 7 ). The composition of saliva is affected by 2 fundamental mechanisms: