|Normal values in saliva|
|In comparison to what is the rule in blood chemistry there are no normal values available for the saliva components. The concentrations of electrolytes, proteins and neutral molecules are relative and depend largely on the behavior of their solvent i.e. water.|
After its formation in the acinus region the primary saliva passes the striated duct and the main ductuli of the salivary gland (the secretory unit). The striated duct has an active lining where sodium reabsorption takes place in exchange for potassium. Some water uptake from the saliva may also be expected. While the primary saliva has electrolyte concentrations near to blood values, low sodium concentrations are apparent after its passage of the striated. Depending on the flow rate the sodium concentration varies from 75 mmol/l after stimulation to 1 mmol/l in rest. The overall outcome is reflected in a decreasing osmolality from 100 mmol/kg to 40 mmol/kg in rest. These changes are highly demanding for the distal ductal epithelial lining. Normally it should be impermeable to small solutes and even to water. Slightly damaging as in inflammation will immediately result in an osmotic gradient with fluid transport to the interstitium.
There are two main standards. The first one is the concentration of solutes, as expressed in mmol/l. Here even large fluctuations may be normal since they are related to the flow rate. The concentration is important in the evaluation of electrolytes and neutral molecules like urea and glucose. The second one is represented in the total production given in volume pro minute or mmol/min. It gives an indication of the vital capacity of the gland and is useful in determining the production of acinar proteins. This may be used to evaluate the tissue destruction in Sjögren's syndrome and after radiation. So the concentration of sodium should be evaluated against the background of a graph compiled from a large group of "normal" patients. In our group the relation to the secretion rate is a straight line between 0,1 and 2,5 ml/min. The sodium concentration is given by f(x) = 30x . Otherwise the normal value of sodium is found by multiplying the measured flow rate in ml/min. with 30. It is important to realize that this is the result of a mean percentage of activated secretory units. Over stimulation tends to activate a larger number of secretory units resulting in leveling the sodium increase. Each of the saliva constituents should be plotted against its own graph to find appropriate normal values. See also the manual.
The attached database provides a group of "normal" patients, i.e. compiled from individuals without any clinical complaint or known disease.