The levels of plasma and erythrocyte ChE activities are well documented, but limited information is available on SChE levels in literature. The reference range of EChE varies with the method of assay, age and sex. The acceptable reference assay values of PChE are based on the Ellman colorimetric method 7 . Bellino et al found a ratio of 2.18 using acetylthiocholine iodide and butyrylthiocholine iodide as substrates for acetylcholinesterase and pseudocholinesterase. Theratio in the present study is 5.97 which is significantly different from the reported values.
Possible explanations are differences in the methods employed, or interlaboratory errors.
This difference may be explained by the small sample size used in Ryhanen studies. Using propylthiocholine as substrate. Among the body fluids, saliva is the most easily available specimen to physicians. The activity of SChE is not greatly affected by salivary flow rate but shows diurnal variation. It has been reported, that the true of type SChE is derived from salivary glandularcells while the pseudo- type of the whole saliva from microorganisms in the oral cavity.