Serum cholinesterase is a test that looks at blood levels of certain enzymes (acetylcholinesterase and pseudocholinesterase) that help the nervous system work properly.

Acetylcholinesterase (also known as RBC cholinesterase) and pseudocholinesterase (also known as butyrylcholinesterase or plasma cholinesterase) help break down a chemical that nerves need to send signals.

Acetylcholinesterase is found in nerve tissue and red blood cells. Pseudocholinesterase is found primarily in the liver.

How the Test is Performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to Prepare for the Test

No special preparation is necessary for this test.

How the Test Will Feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the Test is Performed

This test is done to determine if a person has been exposed to a group of chemicals known as organophosphates, which are used in pesticides. These chemicals turn off cholinesterases. The level of acetylcholinesterase and pseudocholinesterase in your blood can be used to determine your exposure and risk of toxicity.

This test may also be done, although infrequently, to diagnose liver disease. It may also be ordered before a person receives anesthesia with succinylcholine, which may be given before certain procedures or treatments, including electroconvulsive therapy (ECT).

Normal Results

Typically, normal pseudocholinesterase values range between 8 and 18 units per milliliter (U/mL).

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

Decreased pseudocholinesterase levels may be due to:

• Acute infection
• Chronic malnutrition
• Heart attack
• Liver damage
• Metastasis
• Obstructive jaundice
• Poisoning from organophosphates (chemicals found in some pesticides)

Smaller decreases may be due to:

• Pregnancy
• Use of birth control pills

Risks

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken

Alternative Names

Acetylcholinesterase; RBC (or erythrocyte) cholinesterase; Pseudocholinesterase; Plasma cholinesterase; Butyrylcholinesterase