Also Known As
RBC Cholinesterase
Red Cell Cholinesterase
Plasma Cholinesterase
Formal Name
Butyrylcholinesterase; Erythrocyte Acetylcholinesterase
This article was last reviewed on
This article waslast modified on 29 January 2019.
At a Glance
Why Get Tested?

To find out if you are likely to have temporary paralysis after being given a muscle relaxant called suxamethonium during surgery. This temporary paralysis is called suxamethonium apnoea

To screen for exposure to the effects of organic phosphorus insecticides.

When To Get Tested?

If you or a close relative have experienced suxamethonium apnoea after a surgical operation.

To indicate possible insecticide poisoning with recent or frequent use of organic phosphorus insecticides. Occupational exposure can occur in workers involved with agriculture or the organic chemical industry.

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

There are two similar cholinesterase enzymes in the body; butrylcholinesterase (pseudocholinesterase) found in the blood plasma, intestine and white matter of the brain, and acetylcholinesterase found in red blood cells, grey matter of the brain and nerve endings.

Acetylcholine is a chemical which is involved in the transmission of signals across nerve endings and which is broken down by the enzyme acetylcholinesterase. Any decrease in this enzyme can cause a build-up of acetylcholine at nerve endings that in turn can lead to overstimulation of nerves in the body tissues.

Serum butyrylcholinesterase is the enzyme usually measured by the laboratory. This is because the enzyme can be used as a marker for the ineffective metabolism of the muscle relaxant suxamethonium used in surgery as well as exposure to organic phosphorus insecticides.

The laboratory measures the total activity of cholinesterase in the patient’s blood. This is useful because if the activity is low it suggests an atypical enzyme variant is present and that the patient is at risk of prolonged effects from the muscle relaxants suxamethonium or mivacurium. Also, low total enzyme activity in people working with organophosphorus compounds on farms or in the chemical industry may indicate acute exposure.

Inhibitor studies are also carried out to determine the patient’s phenotype which can be used to find out whether the enzyme is ‘usual’ or ‘atypical’ , provide more information about any potential risk and assist in family studies. In order to identify the cholinesterase phenotype the enzyme is incubated with a range of inhibitors which include dibucaine, fluoride and frequently Ro 02-0683, chloride and sometimes scoline. The percentage of the enzyme activity remaining is referred to as a ‘number’ and is used to assess the phenotype. In this way the laboratory can discover whether the patient has a usual (normal) or an atypical enzyme. The enzyme phenotype can be further classified into a number of possible variants with varying degrees of possible sensitivity to suxamethonium or mivacurium.

Genetic studies can also be indicated if an ‘atypical’ variant is difficult for the laboratory to identify or if a silent S gene is suspected. These tests are not as widely available as phenotype studies at present.

How is the sample collected for testing?

A blood sample taken from a vein in your arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

Accordion Title
Common Questions
  • How is it used?
    • Cholinesterase activity and phenotype studies in a patient can be used to predict the degree of potential post-operative paralysis following the use of the short reacting muscle relaxant suxamethonium or mivacurium.
    • Cholinesterase can be used as a monitor of exposure to organic phosphorus compounds in the agricultural and chemical industries.
  • When is it requested?
    • Pre-operative screening for cholinesterase activity and phenotype is advised if the patient or a close family member has experienced prolonged paralysis after an operation that required ventilation support up to several hours after surgery
    • People using organic phosphorus compounds such as Parathion, Sarin or tetraethyl pyrophosphate in the farming or chemical industries may be routinely monitored to assess any adverse exposure once baseline levels are established. Cholinesterase activity can also be used to assess any acute exposure to these compounds which can cause neuromuscular damage. Toxicity can follow a rapid absorption of the compound in the lungs, skin or gastrointestinal tract. The symptoms of toxicity are varied, ranging from vomiting to paralysis or coma, and depend on the compound, quantity and the site of exposure.
  • What does the test result mean?
    • The degree of sensitivity to suxamethonium varies according to the patient’s phenotype. The risk of paralysis in individuals with a usual (UU) phenotype is extremely rare whereas UA or UF phenotypes may carry a small risk of an increased recovery time of about half an hour if suxamethonium is used during pregnancy, say during a caesarean section. Individuals with atypical phenotypes can experience prolonged paralysis of 2 or more hours with the silent phenotype over three hours. The other fluoride phenotypes FF, FS and AF tend to experience an intermediate sensitivity to suxamethonium.
    • Following exposure to organic phosphorus compounds, serum cholinesterase can fall to about 40% before any symptoms occur and an 80% drop before the symptoms become severe.
  • Is there anything else I should know?

    Total cholinesterase activity can also be lowered in a number of other conditions. These include pregnancy, renal disease, shock, malnutrition and some cancers.

    As cholinesterase is synthesised by the liver the activity can also be lower in some liver diseases such as acute and chronic hepatitis, advanced cirrhosis and liver metastases. However, normal levels can be found in mild hepatitis and cirrhosis as well as obstructive jaundice.

    There may be a risk of a very mild prolonged reaction to suxamethonium in these conditions of minutes as opposed to hours, as long as these patients have lower activities of the usual enzyme rather than the atypical enzyme variant

  • Should everyone be tested for cholinesterase?

    No. It should be tested if the individual or close family member has experienced post operative paralysis requiring ventilation or if someone is in potential contact with organic phosphorus chemicals regularly in the workplace.

  • What happens if I have an atypical phenotype?

    The report from the laboratory will be sent to the requesting doctor and placed in your medical notes. You should also be given a medical warning card that can be shown to any surgical team in the future to enable the anaesthetist to give a safe muscle relaxant for you.

  • What is a cholinesterase genotype?

    These are the genes for cholinesterase inherited by someone from their parents. This can be established in the laboratory using DNA techniques.

  • What is a cholinesterase phenotype?

    This can be determined by defining the properties of the enzyme protein structure. The phenotype is derived by measuring the response of the cholinesterase enzyme to a range of enzyme inhibitors.