The application of saliva, sweat and tear fluid for diagnostic purposes

Despite anatomical and biochemical similarities, salivary, sweat and lacrimal glandulas differ in their physiological functions. Salivary and tear fluid are required for the proper function of the epithelial layer from which they are secreted. The physiological function of sweat is the elimination of excess heat. The products of the three glandulas can be used to measure indicators either of glandula or of non-glandular diseases. In the latter case the indicator must be transported from the particular organ to the glandula where it is then secreted. In sweat, only one example has reached well accepted clinical importance. The measurement of electrolyte concentrations is the classical laboratory test for cystic fibrosis. The use of tears for diagnostic purposes has been proposed for drug monitoring, to verify the dry eye syndrome (Schirmer test), to detect lysosomal storage diseases (eg Morbus Gaucher) and hyperglycemia. The major domains for the application of saliva are hormone analyses (especially of steroids) and drug monitoring. Furthermore, the application of saliva has been proposed for the detection of several other analytes (eg secretory IgA, peptide hormones, HIV antibodies).