Overview
Cholinesterase refers to a group of enzymes that hydrolyze esters of choline into acetic acid and choline. These enzymes play a vital role in nervous system function by regulating the neurotransmitter acetylcholine. Common synonyms include acetylcholinesterase, red blood cell (RBC or erythrocyte) cholinesterase, pseudocholinesterase, plasma cholinesterase, and butyrylcholinesterase.
Two major types are clinically significant: acetylcholinesterase, primarily found in red blood cells, and butyrylcholinesterase, found in plasma. The primary function of acetylcholinesterase is to terminate neuronal transmission at synapses, preventing excessive stimulation of receptors. When this enzyme activity is inhibited, acetylcholine accumulates, leading to altered nerve signaling.
Acetylcholine itself is an important neurotransmitter involved in memory, learning, attention, arousal, and involuntary muscle movement. Reduced levels of acetylcholine are associated with conditions such as Alzheimer’s disease and myasthenia gravis.
Serum cholinesterase testing is used in several clinical situations, including the diagnosis of liver disease, evaluation before administering anesthesia with succinylcholine, confirmation of organophosphate or carbamate poisoning, monitoring treatment with atropine in poisoning cases, and supporting the diagnosis of Alzheimer’s disease and myasthenia gravis.
Symptoms
These abnormalities do not produce direct symptoms; rather, symptoms arise from the underlying conditions associated with altered enzyme levels. In cases of poisoning, reduced cholinesterase activity reflects excessive acetylcholine accumulation, which can result in neuromuscular and autonomic disturbances. In chronic or neurological conditions such as Alzheimer’s disease or myasthenia gravis, symptoms are linked to impaired acetylcholine function, affecting memory, learning, muscle strength, and neuromuscular transmission.
Causes
Decreased cholinesterase levels can occur due to various medical conditions and physiological states. Major causes include hereditary deficiency of pseudocholinesterase, chronic infections, chronic malnutrition, heart attack, liver damage, metastasis, obstructive jaundice, and poisoning from organophosphates, which are chemicals commonly found in some pesticides.
Inflammation associated with certain diseases can also reduce enzyme levels.
Smaller decreases in this activity may be seen during pregnancy or with the use of birth control pills. Additionally, serum cholinesterase levels may be reduced in patients taking estrogens or oral contraceptives.
Risk Factors
Risk factors for altered levels include exposure to organophosphorous or carbamate pesticides, underlying liver disease, chronic illnesses, malnutrition, and genetic enzyme deficiencies. Individuals undergoing anesthesia with succinylcholine are at risk if pseudocholinesterase deficiency is present, as this can prolong drug effects. Chronic exposure to toxic chemicals increases the risk of significant enzyme suppression. Physiological states such as pregnancy and hormonal medication use also influence enzyme levels.
Laboratory interpretation may be affected by red blood cell destruction or reduced red cell synthesis, such as in anemia, which is why both plasma and whole blood samples are required for accurate assessment.
Prevention
Prevention focuses on reducing exposure to known risk factors and ensuring proper clinical evaluation. Avoiding or minimizing exposure to organophosphate pesticides and other toxic chemicals is essential. Prior assessment levels before administering certain anesthetic agents help prevent complications. Proper nutritional status and management of chronic diseases contribute to maintaining normal enzyme levels.
Accurate testing and monitoring are supported by appropriate sample collection, including collecting blood in EDTA tubes, separating plasma promptly, and submitting both plasma and whole blood samples to account for variations related to red blood cells and hemoglobin levels. Awareness of test limitations, such as interference from fluoride and the effects of hormonal medications, is also important for correct interpretation.
