Hench-Aldrich Salivary Index

[The Hench-Aldrich salivary index is a method that, by determining the content of urea and] its breakdown products in saliva, judges the degree of residual nitrogen retention in the body. The determination is performed as follows: saliva is titrated with a 5% solution of mercuric chloride, which precipitates urea and its hydrolysis products. The completion of the precipitation reaction is indicated by the appearance of a brown coloration of a drop of the titrated liquid, taken onto the lid of a crucible and mixed with an indicator (a 7% solution of anhydrous or a 20% solution of crystalline soda). The number of cubic centimeters of mercuric chloride solution spent on precipitation and converted to 100 cubic centimeters of saliva represents the salivary index, or the indicator of the patient under examination. In a healthy person, the normal Hench-Aldrich salivary index is 25-35, i.e., 1.25-1.75 cubic centimeters of mercuric chloride solution per 5 cubic centimeters of saliva, or 2.5-3.5 cubic centimeters per 10 cubic centimeters. With large retentions of residual nitrogen, the Hench-Aldrich salivary index reaches 240-260. While usually increasing in parallel with the increase of urea in the body, the salivary index does not, however, provide complete numerical correspondence with it, since saliva, in addition to urea, contains insignificant amounts of amino acids, creatinine, uric acid, and mucin, and in some cases, insignificant amounts of protein, which affects the Hench-Aldrich salivary index. Furthermore, when saliva stands, a portion of the urea is destroyed by hydrolysis caused by bacteria and, converting into ammonia, volatilizes. The character of the saliva (its viscosity) has only an insignificant influence on the Hench-Aldrich salivary index. While not an absolutely precise indicator of the urea content in the blood, and fluctuating within small limits due to a whole range of external and internal conditions for the body, the salivary index usually provides a clear answer, indicating a normal or elevated content of urea in the body. An increase or decrease in the numerical value of the salivary index provides an idea of the fluctuations of urea, respectively residual nitrogen, in the body, indicating even relatively small retentions. The simplicity of the examination, which requires neither special preparation nor complex instrumentation, the ease of obtaining the test material, as well as the necessity for every practicing physician to have in hand a method for determining the functional capacity of the kidneys in relation to the excretion of nitrogen, allow the Hench-Aldrich salivary index method to be considered quite suitable for practical purposes that do not claim scientific precision.