A RADIOMETRIC METHOD FOR ESTIMATING BLOOD CHOLINESTERASE IN THE FIELD.

A radiometric method has been developed which provides for the simple and rapid measurement of human blood cholinesterase under field conditions. The method involves minimal dilution of samples and the use of very low substrate concentrations, and is therefore more sensitive to cholinesterase inhibition by reversible anticholinesterases such as carbamates than the conventional manometric or DeltapH methods. A 20-mul sample of haemolysed whole blood is mixed with (14)C-labelled acetylcholine on a cavity microscope slide. After half a minute or three minutes the mixture is acidified and dried. Under these conditions radioactive acetate liberated enzymically is completely volatile while the radioactive unhydrolysed substrate is not. The loss of radioactivity on acidification and drying is therefore a direct measure of the acetylcholinesterase activity. The levels of radioactivity employed are far below those likely to present any significant health hazard or to require special laboratory conditions. Although the method requires a labelled substrate, a single preparation is sufficient for several hundred thousand enzyme assays. The method has been tested under simulated field conditions.