Tuesday, October 30, 2007
Clinical Biochemistry
Cholinesterase
Cholinesterase is an enzyme which catalyzes the hydrolysis of acetylcholine into choline and acetic acid, allowing a cholinergic neuron to return to its resting state after activation. It is crucial to the transmission of electrical impulses along the nerves and also indicates the liver capacity for synthesis.
There are 2 types of cholinesterase: plasma or pseudo-cholinesterase and acetylcholinesterase which are found in the blood (RBCs) and nerves.
Individuals exposed to organophosphorous compounds (e.g. insecticides) exhibit decreased levels of cholinesterase in RBCs and serum. Acetylcholine activity is a better marker for insecticide poisoning, because some individuals may have normal or near normal levels of total serum cholinesterase. However, others have recommended that the serum enzyme measurements reflect acute poisoning while RBC cholinesterase measurement is useful for long-term chronic exposure to insecticides.
Cholinesterase measurements are also used in the detection of patients with inherited abnormal variants of the enzyme. In the nerve endings, reduced cholinesterase activity results in accumulation of acetylcholine which triggers excessive stimulation.
Clinical manifestations for acute insecticide poisoning include excessive salivation, nausea, vomiting, diarrhea, abdominal cramping and asthmatic symptoms. For the cardiovascular system, bradycardia, arrthymias and pulmonary edema are some problems that may happen. Overstimulation of muscarinic sites in the CNS can cause confusion, ataxia and slurred speech. Death may occur.
Procedure for RBC cholinesterase
1. Patient’s blood in EDTA tube is poured into a glass test tube and filled to ¾ with 0.9% saline.
2. The suspension is mixed well by inverting several times and centrifuged at 3500rpm for 5 minutes.
3. Using the suction pump, the plasma and buffy coat (layer on top of RBCs) are removed.
4. 0.9% saline and spun cells are pipetted into a secondary tube to obtain a 1:1 dilution.
5. 0.5% saponin (lysing agent) and the suspension are pipetted into a new secondary tube.
6. The hemolysate is incubated in a refrigerator (2-8°C) for 10 minutes before analyzed on the Beckman Coulter LX20U analyzer.
7. The PCV (hematocrit) is measured using the suspension (obtained in Step 4). The blood is put into capillary tubes and centrifuged at 13000rpm for 5 minutes and the PCV is read off a calibrator rule.
As cholinesterase activity is expressed in activity units with respect to PCV, both enzyme activity and PCV for the hemolysate are determined. After getting the results, the formula [(Cholinesterase/PCV) X 100] is used to obtain the RBC cholinesterase level.
The reference interval for RBC cholinesterase is 15000-24000 U/L RBC.
Note: Serum cholinesterase is also measured in the laboratory, but on the Johnson & Johnson Vitros DT60 II. Information about this analyzer can be found more in 77th Medical Technologist Street blog post on the 5th week.
Cholinesterase is an enzyme which catalyzes the hydrolysis of acetylcholine into choline and acetic acid, allowing a cholinergic neuron to return to its resting state after activation. It is crucial to the transmission of electrical impulses along the nerves and also indicates the liver capacity for synthesis.
There are 2 types of cholinesterase: plasma or pseudo-cholinesterase and acetylcholinesterase which are found in the blood (RBCs) and nerves.
Individuals exposed to organophosphorous compounds (e.g. insecticides) exhibit decreased levels of cholinesterase in RBCs and serum. Acetylcholine activity is a better marker for insecticide poisoning, because some individuals may have normal or near normal levels of total serum cholinesterase. However, others have recommended that the serum enzyme measurements reflect acute poisoning while RBC cholinesterase measurement is useful for long-term chronic exposure to insecticides.
Cholinesterase measurements are also used in the detection of patients with inherited abnormal variants of the enzyme. In the nerve endings, reduced cholinesterase activity results in accumulation of acetylcholine which triggers excessive stimulation.
Clinical manifestations for acute insecticide poisoning include excessive salivation, nausea, vomiting, diarrhea, abdominal cramping and asthmatic symptoms. For the cardiovascular system, bradycardia, arrthymias and pulmonary edema are some problems that may happen. Overstimulation of muscarinic sites in the CNS can cause confusion, ataxia and slurred speech. Death may occur.
Procedure for RBC cholinesterase
1. Patient’s blood in EDTA tube is poured into a glass test tube and filled to ¾ with 0.9% saline.
2. The suspension is mixed well by inverting several times and centrifuged at 3500rpm for 5 minutes.
3. Using the suction pump, the plasma and buffy coat (layer on top of RBCs) are removed.
4. 0.9% saline and spun cells are pipetted into a secondary tube to obtain a 1:1 dilution.
5. 0.5% saponin (lysing agent) and the suspension are pipetted into a new secondary tube.
6. The hemolysate is incubated in a refrigerator (2-8°C) for 10 minutes before analyzed on the Beckman Coulter LX20U analyzer.
7. The PCV (hematocrit) is measured using the suspension (obtained in Step 4). The blood is put into capillary tubes and centrifuged at 13000rpm for 5 minutes and the PCV is read off a calibrator rule.
As cholinesterase activity is expressed in activity units with respect to PCV, both enzyme activity and PCV for the hemolysate are determined. After getting the results, the formula [(Cholinesterase/PCV) X 100] is used to obtain the RBC cholinesterase level.
The reference interval for RBC cholinesterase is 15000-24000 U/L RBC.
Note: Serum cholinesterase is also measured in the laboratory, but on the Johnson & Johnson Vitros DT60 II. Information about this analyzer can be found more in 77th Medical Technologist Street blog post on the 5th week.
Martin Ng
TG02
0503312A
# posted by Star team @ 8:18 PM 
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yo mart,
just wanna if the result exceeds the reference range, do you have to report to the doctor?
thanks
randall
tg02
just wanna if the result exceeds the reference range, do you have to report to the doctor?
thanks
randall
tg02
Hey randall,
Low amounts of cholinesterase will pose danger to the patient. However, if the results exceeds the reference range, we do not have to report to the doctor.
Martin
TG02
Low amounts of cholinesterase will pose danger to the patient. However, if the results exceeds the reference range, we do not have to report to the doctor.
Martin
TG02
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