Clinical Information

Serum cholinesterase, often called pseudocholinesterase (PCHE), is distinguished from acetylcholinesterase, or "true cholinesterase," by both location and substrate.

Acetylcholinesterase is found in erythrocytes, lungs and spleen, nerve endings, and gray matter of the brain. It is responsible for the hydrolysis of acetylcholine released at the nerve endings to mediate transmission of the neural impulse across the synapse.

PCHE, the serum enzyme, is found in the liver, pancreas, heart, and white matter of the brain. Its biological role is unknown.

The organophosphorus-containing insecticides and herbicides are potent inhibitors of the true cholinesterase and cause depression of PCHE. Low values of PCHE are also found in patients with liver disease. In general, patients with advanced cirrhosis and carcinoma with metastases will show a 50% to 70% decrease. Essentially normal values are seen in chronic hepatitis, mild cirrhosis, and obstructive jaundice.

PCHE metabolizes the muscle relaxants succinylcholine and mivacurium, and therefore, alterations in PCHE will influence the physiologic effect of these drugs.

In normal individuals (approximately 94% of the population), certain drugs and other agents such as dibucaine and fluoride will almost completely inhibit the PCHE activity.

A small number of individuals (<1% of the population) have been shown to have genetic variants of the enzyme and, therefore, cannot metabolize the muscle relaxants succinylcholine and mivacurium and experience prolonged apnea. These individuals generally have low levels of PCHE, which is not inhibited by dibucaine or fluoride. These individuals are either homozygous or compound heterozygous for an atypical gene controlling PCHE.

Simple heterozygous individuals have also been identified who show intermediate enzyme values and inhibition.