Cholinesterase

Sample for Cholinesterase

1. It is done on the serum of patients.
2. Enzyme activity in the serum is stable for several weeks.
   1. Another reference says
      1. stable for 6 hours at room temperature.
      2. One week at 4 °C.
      3. 6 months at -70 °C
3. The serum is stable at room temperature and also on refrigeration.

Precautions for Cholinesterase

1. Avoid hemolysis.
2. Avoid repeated freezing and thawing.
3. Pregnancy decreases test value.
4. Drugs that may cause a decrease in the test values are atropine, caffeine, codeine, morphine, oral contraceptives, theophylline, quinidine, estrogen, and vitamin K.

Indications for Cholinesterase

1. Advised when you are exposed to chemicals called organophosphates, which are used in pesticides. This test can help determine your risk of poisoning.
2. This test is done to rule out poisoning (Organophosphorus).
   1. For insecticide poisoning.
      1. e.g., parathion, sarin, and tetraethyl pyrophosphate.
3. To diagnose liver disease.
4. Before you receive anesthesia with succinylcholine, which may be given before certain procedures or treatments, including electroconvulsive therapy (ECT).
   1. Particularly in the case of pseudocholinesterase deficiency before the anesthesia.
5. Monitoring patients with liver disease, particularly those undergoing liver transplantation.
6. Identifying patients who are homozygous or heterozygous for an atypical gene with low pseudocholinesterase levels.

Definition of cholinesterase

1. Cholinesterase hydrolyzes acetylcholine and other choline esters; as a result, it regulates nerve impulse transmission at the nerve synapses and neuromuscular junctions.
2. Acetylcholine is the transmitter substance that is released at motor neuron end-plate-end-plate by an electrical impulse traveling down the nerve toward a muscle.
3. The function of the neurotransmitter is to propagate an electrical impulse from one neuron to another neuron.
4. Acetylcholinesterase exists in RBCs and at nerve endings.
5. Two enzymes can hydrolyze acetylcholine.

Pathophysiology of Cholinesterase 

1. Acetylcholine diffuses from the nerve endings to the muscles and causes electrical depolarization of muscle cells followed by muscle contraction.
   1. Acetylcholine is rapidly broken down to acetate and choline by the enzyme acetylcholinesterase at the post-synaptic site to finish the process.
   2. Failure to inactivate acetylcholine results in muscular paralysis.
2. Cholinesterase is primarily not found in the serum, while pseudocholinesterase is found in the serum.
3. Serum cholinesterase is a test that looks at blood levels of enzymes like Acetylcholinesterase and pseudocholinesterase.
4. Cholinesterase is an enzyme of the hydrolase group.
   1. It can catalyze the breakdown of an acyl group from various esters of choline and acetylcholine.
5. Cholinesterase is of two types:
   1. Acetylcholinesterase.
      1. This is also known as true cholinesterase.
   2. Pseudocholinesterase in the serum is derived from the liver.
   3. It is the first noticeable neurotransmitter and is formed in presynaptic cholinergic neurons from acetyl-CoA derived from lipid metabolism.
   4. Pseudocholinesterase.

Enzymes inhibitors are:

1. The alkaloids prostigmine and physostigmine inhibit both enzymes.
2. Both enzymes are inhibited irreversibly by some organic phosphorus compounds, such as diisopropyl fluorophosphate.
3. Both enzymes are also inhibited by many compounds like morphine, tertiary amines, quinine, phenothiazines, pyrophosphate, citrate, bile salt, borate, and fluoride.

Cholinesterase enzyme distribution and functions:

1. The cholinesterase enzyme breaks down acetylcholine.
2. Acetylcholinesterase is found in nerve tissue, red blood cells, and the lung and spleen.
3. It is present in the grey matter of the brain.
4. Pseudocholinesterase is found primarily in the liver.
5. It is also present in the pancreas, heart, white matter of the brain, and serum.
6. These enzymes help the nervous system to work correctly.
   1. Acetylcholinesterase and pseudocholinesterase are needed to send signals through nerves.
7. Acetylcholinesterase in RBCs is known as RBC cholinesterase.

Acetylcholine and cholinesterase functions

8. Pseudocholinesterase, known as butyrylcholinesterase or plasma cholinesterase, helps break down a chemical that nerves need to send signals.

Cholinesterase types and distribution

9. The difference between the two types of cholinesterase depends on their respective preferences for substrates.
   1. Acetylcholinesterase hydrolyzes acetylcholine more quickly.
   2. Pseudocholinesterase hydrolyzes butyrylcholine more quickly.
   3. The half-life of pseudocholinesterase is approximately 8–16 hours.
   4. Pseudocholinesterase levels may be reduced in patients with advanced liver disease.
10. The decrease must be greater than 75% before significant prolongation of neuromuscular blockade occurs with succinylcholine.

cholinesterase Deficiency

9. Elevation of plasma pseudocholinesterase was observed in 90.5% of cases of acute myocardial infarction.
10. Acetylcholinesterase can confirm several common types of birth defects, including abdominal wall and neural tube defects.

Signs and symptoms of deficiency of Cholinesterase:

1. A 40% drop in serum enzyme activity occurs before the first symptoms are noted.
   1. A drop of 80% is needed before the neuromuscular signs are noted.
   2. Near  0% enzyme activity needs emergency treatment of the patient with enzymes like pyridine-2-aldoxime.
2. Pseudocholinesterase deficiency is present in a patient, and if these patients are given anesthesia drugs, these will not break down and lead to prolonged action.
   1. As a result, the muscles are relaxed, and the patient has difficulty in breathing and movements.

Normal Cholinesterase

Source 1

1. Serum cholinesterase =  8 to 18 units/mL (8 to 18 units/L).
   1. RBC cholinesterase = 5 to 10 units/mL (30 to 40 units/g of the hemoglobin).
2. Typically, normal pseudocholinesterase values range between 8 and 18 units/mL.
   1. The values are low at birth and the first 6 months of life.
   2. Reference values have not been established for patients who are <18 years of age.

Source 2

• 4.9 to 11.9 U/mL
• values are low at birth and the first 6 months of life, increasing to 30 to 50% above adult values until 5 years,  then gradually decreasing to adult values by puberty.
• (Values vary according to the type of methodology used.)

The serum increased level of Cholinesterase is seen in:

1. Nephrosis.
2. Diabetes mellitus.
3. Hyperlipidemia.

The serum decreased level of Cholinesterase is seen in:

1. Poisoning with organophosphate insecticide.
2. Liver diseases like hepatitis.
3. Cirrhosis with ascites or jaundice.
4. Metastatic carcinoma.
5. Obstructive jaundice.
6. Congestive heart failure.
7. Before you receive anesthesia with succinylcholine, which may be given before certain procedures or treatments, including electroconvulsive therapy (ECT).
8. In conditions with low serum albumins like malnutrition, anemia, infections, Dermatomyositis, Acute MI, and liver diseases.

The Smaller decrease may be due to:

1. Pregnancy.
2. Use of birth control pills.

RBC increased level is seen in:

1. Reticulocytosis.
2. Sickle cell anemia.

RBC decreased level is seen in:

1. Poisoning is due to insecticides like organophosphorus.
2. Congenital cholinesterase deficiency.

• Critical value:
  • The persistently low level of liver disease indicates a poor prognosis.

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