Cholinesterase, Serum

Laboratory assay overview

This test is used to evaluate preoperative patients for succinylcholine (suxamethonium) anesthetic sensitivity, genetic or secondary to insecticide exposure, in appropriate circumstances, and to prevent or evaluate prolonged anesthetic effect, prolonged apnea, after surgery. Very small amounts (0.04−0.06 mg/kg) of succinylcholine are needed to obtain 90% of neuromuscular blockade in patients with low levels of plasma cholinesterase activity.1 Monitor organophosphorous or carbamate insecticide poisoning, in which level is decreased; establish patient's baseline value before exposure. Indications include such pesticide exposure, especially with miosis, blurred vision, muscle weakness, twitching, and fasciculation, bradycardia, nausea, diarrhea, vomiting, salivation, sweating, pulmonary edema, arrhythmias, and convulsions. The value of assessing risk status in persons exposed to organophosphate insecticides on the basis of plasma or serum cholinesterase levels alone has been called into question.2 Are normal levels indicative of no exposure or of a genetic variant with or without exposure? There are interpretive problems with low or high values.2 Family studies may be done when an individual with a genetically abnormal type is documented by serum pseudocholinesterase deficiency and, ideally, confirmed by phenotyping.

Laboratory assay overview

Approximately 1 in every 2500 individuals has inherited defective or deficiency of the enzyme (pseudocholinesterase) that metabolizes succinylcholine (an anesthetic agent). With "normal" dosage, these individuals have prolonged apnea. Such individuals are responsive at much smaller concentrations of this anesthetic agent than the general population. Low concentrations of pseudocholinesterase are observed in individuals exposed to organophosphorous insecticides and patients with hepatic dysfunction.

Laboratory assay overview

This test may be used to detect exposure to or poisoning from organophosphate-based pesticides; to assess baseline levels before exposure to organophosphates; or to monitor cholinesterase levels in individuals who work with pesticides. This test is also used in the diagnosis of inherited pseudocholinesterase deficiency, for individuals with a family history who will be receiving the muscle relaxant succinylcholine during surgery. The Cholinesterase, Serum assay is often used as part of the diagnostic evaluation for individuals who present with symptoms of pesticide poisoning. Symptoms of organophosphate poisoning can range from mild to severe and may include sweating, salivation, miosis, hypotension, urinary incontinence, mental confusion, gastrointestinal spasms, anxiety, insomnia, tremors, convulsions, respiratory depression, and circulatory collapse, among others [1]. This test is also used in the diagnosis of inherited pseudocholinesterase deficiency, an enzyme deficiency characterized by impaired metabolism of succinylcholine, a muscle relaxant for surgical anesthesia. Individuals with this disorder who receive succinylcholine are at risk for prolonged postsurgical apnea and paralysis lasting 2 or more hours [2]. Thus, testing may be helpful to evaluate individuals who present with these symptoms postsurgically, as well as those with a family history of pseudocholinesterase deficiency who are scheduled for surgery. References 1. Lessenger JE, Reese BE. J Am Board Fam Pract. 1999;12:307-314. 2. Soliday FK, et al. AANA J. 2010;78:313-320.