What is Cholinesterase (Pseudocholinesterase)?

Also Known As: CHS, AChE, RBC Cholinesterase, Red Cell Cholinesterase, BChE, Plasma Cholinesterase, Pseudocholinesterase, PCHE

Formal Name: Erythrocyte Acetylcholinesterase, Butyrylcholinesterase

Cholinesterases are enzymes that are involved in helping the nervous system to function properly. There are two separate cholinesterase enzymes in the body: (1) acetylcholinesterase, found in red blood cells as well as in the lungs, spleen, nerve endings, and the gray matter of the brain, and (2) pseudocholinesterase (butyrylcholinesterase), found in the serum as well as the liver, muscle, pancreas, heart, and white matter of the brain. Cholinesterase tests measure the activity of these enzymes.

Acetylcholinesterase is involved in the transmission of nerve impulses by breaking down acetylcholine, a chemical that helps to transmit signals across nerve endings. A decrease in the activity of the enzyme acetylcholinesterase results in excess acetylcholine at nerve endings. This can lead to overstimulation of nerves within body tissues and organs. Pseudochlinesterase is involved in the processing and metabolizing of drugs.

The two most common reasons for testing activity levels in the blood are:

• Organophosphate pesticide exposure. Insecticides containing organophosphates can inhibit cholinesterase and pseudocholinesterase activity. Symptoms can be severe with acute exposure to these pesticides or can gradually appear with chronic exposure. Absorption can occur by inhalation, ingestion, or contact with the skin. Testing red blood cell acetylcholinesterase and serum pseudocholinesterase may be done to detect acute poisoning or to monitor those with occupational exposure to these chemicals, such as farmworkers or those who work with industrial chemicals.
• Inherited pseudocholinesterase deficiency. Some individuals have an inherited deficiency due to a genetic variant of the enzyme pseudocholinesterase. This enzyme is used by the body to inactivate (metabolize) succinylcholine, a muscle relaxant that is commonly used during surgery. People who have low levels or defective pseudocholinesterase may experience prolonged effects of the drug, with protracted muscle paralysis and apnea following anesthesia. In addition, those who are homozygous for genetic variants may be at greater risk of adverse effects than those who are heterozygous. Pseudocholinesterase testing can be performed prior to surgery on those with a family history of prolonged apnea after the use of succinylcholine to determine if they are at risk of complications related to this drug.

How is it used?

Cholinesterase testing has two main uses:

• It can be used to detect and diagnose organophosphate pesticide exposure and/or poisoning. It may also be used to monitor those who may be at increased risk of exposure to organophosphate compounds, such as those who work in agricultural and chemical industries and to monitor those who are being treated for exposure. Typically, tests for red blood cell acetylcholinesterase (AChE) and serum pseudocholinesterase (PChE) are used for this purpose.
• It can be used several days prior to a surgical procedure to determine if someone with a history of or family history of post-operative paralysis following the use of succinylcholine, a common muscle relaxant used for anesthesia, is at risk of having this reaction. In these cases, the test for pseudocholinesterase is usually used. A second test referred to as a dibucaine inhibition test may be done to help determine the extent to which the activity of the enzyme is decreased.