Improved colorimetric method for cholinesterase activity.

A modified colorimetric method for the estimation of cholinesterase activity has been worked out using two different substrates, acetylthiocholine iodide for total cholinesterase and a specific substrate, butyrylthiocholine iodide for pseudocholinesterase in the same sample. This is a modification of the method described by Voss and Sachsse (1970) wherein acetylthiocholine iodide was used for both total and pseudo cholinesterase activities. The pseudocholinesterase obtained with acetylthiocholine iodide was significantly higher (P < 0.0001) than that with butyrylthiocholine iodide either in whole blood or serum samples. Acetylthiocholine iodide while reacting with pseudocholinesterase in serum or plasma samples might also be interacting with the small quantities of acetylcholinesterase present. It is therefore suggested that butyrylthiocholine iodide and acetylthiocholine iodide may be used to determine pseudocholinesterase and total cholinesterase activities respectively. The use of two substrates with a few more alterations in the experimental conditions increased the validity of this simple and rapid colorimetric method.