Cholinesterase is a term, which encompasses two enzymes; Acetylcholinesterase and Pseudocholinesterase. Both of these catalyse the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid.
Pseudocholinesterase is formed in the liver, pancreas, heart and brain white matter, (not to be confused with acetylcholinesterase [true cholinesterase] which is found in the RBC’s and CSF). It is essential for the degradation of acetylcholine (the chemical responsible for transmitting the nerve impulse from nerve to muscle fibre), after impulse transmission has been mediated. This allows repolarization, ready for the next impulse.
The gene controlling the synthesis of the enzyme uses at least two alleles. Genetic defects can therefore produce many forms of the enzyme, which have slightly different properties, including characteristic inhibition by various substances (e.g. fluoride). An absence or mutation of the pseudocholinesterase enzyme leads to a condition known as partial or complete pseudocholinesterase deficiency. This is a silent condition that only manifests itself when people who have the deficiency receive succinylcholine or mivacurium during surgery. The muscle relaxant suxamethonium ion, when used in anaesthesia is rapidly degraded by cholinesterase and only allows the drug 2-5 minutes physiological activity. In those patients with a genetically affected enzyme with reduced activity, the effect is to extend the duration of drug action, resulting in apnoea.
The method described follows the disappearance of the substrate benzoylcholine at 240nm. The rate of change is used to calculate total enzyme activity. The activity is also measured after inhibition by fluoride, dibucaine and RO –02-0683 to give the fluoride, dibucaine, and RO numbers.
- A serum sample is required for analysis (SST or Plain container)
- Three patient identifiers from
- N.H.S. number
- Unit Number