SERUM CHOLINESTERASE - Acetylcholinesterase is and enzyme found in nerve tissue while pseudocholinesterase is an enzyme found primarily in the liver. Both of these enzymes normally breakdown the neurotransmitter acetylcholine. Medical tests are available which measure acetylcholinesterase and pseudocholinesterase levels in the body. This test may be performed as a screening tool prior to the administration of electroconvulsive therapy (ECT). It is also useful in identifying organophosphate toxicity or congenital enzyme deficiencies.