Unit Converter
Cholinesterase
(Pseudocholinesterase / Butyrylcholinesterase – Liver Function & Organophosphate Exposure Marker)
Synonyms
- Cholinesterase
- Pseudocholinesterase (PChE)
- Butyrylcholinesterase (BChE)
- Plasma cholinesterase
- Serum cholinesterase
- Non-specific cholinesterase
(Note: Acetylcholinesterase = RBC cholinesterase; different enzyme.)
Units of Measurement
- nkat/L
- µkat/L
- nmol/(s·L)
- µmol/(s·L)
- U/L
- IU/L
- µmol/(min·L)
- µmol/(h·L)
- µmol/(h·mL)
Description
Cholinesterase (pseudocholinesterase) is a liver-synthesized enzyme that hydrolyzes choline-based esters. It is distinct from acetylcholinesterase, which is present in nerve tissue and RBCs.
Major clinical roles:
- Evaluation of organophosphate & carbamate poisoning
- Assessment of liver synthetic function
- Genetic cholinesterase deficiency (succinylcholine sensitivity)
- Monitoring exposure in agricultural workers
Cholinesterase is depressed in poisoning because organophosphate compounds irreversibly inhibit the enzyme.
Physiological Role
- Detoxification of ester-based drugs (succinylcholine, mivacurium)
- Hydrolysis of choline esters in plasma
- Protects cholinergic synapses from overstimulation
- Indicator of liver synthetic capacity (decreases when liver fails)
Clinical Significance
Low Cholinesterase Levels (Most Important)
1. Organophosphate / Carbamate Poisoning
- Marked reduction in enzyme activity
- Used for diagnosis & monitoring
- Correlates with severity
- Enzyme activity recovers slowly (2–4 weeks)
2. Liver Disease
Low in:
- Cirrhosis
- Hepatitis
- Liver failure
- Malnutrition
- Alcoholic liver disease
3. Genetic Variants (Pseudocholinesterase Deficiency)
- Leads to prolonged apnea after succinylcholine during anesthesia
- Dibucaine inhibition test helps identify variants
- Causes:
- Atypical enzyme
- Silent enzyme
- Fluoride-resistant enzyme
- Atypical enzyme
4. Pregnancy
Levels fall by 20–40% during third trimester.
5. Drugs
Decreased by:
- Oral contraceptives
- Estrogen therapy
- MAO inhibitors
- Anticholinesterases
- Cytotoxic drugs
High Cholinesterase Levels
Seen in:
- Obesity
- Diabetes
- Nephrotic syndrome
- Hyperthyroidism
- Chronic alcoholism
High levels are less clinically significant.
Reference Intervals
(Tietz 8E + IFCC + Mayo + ARUP)
Values vary by method; typical adult ranges:
Men
- 5,000 – 12,000 U/L
Women
- 4,000 – 11,000 U/L
Pregnancy
- Reduced (up to 40% lower)
(Direct katals depend on assay conditions; see conversion section.)
Summary Table
| Unit | Meaning |
| nkat/L | nanokatal per liter |
| µkat/L | microkatal per liter |
| nmol/(s·L) | nanomole per second per liter |
| µmol/(s·L) | micromole per second per liter |
| U/L | unit per liter (µmol/min/L) |
| IU/L | identical to U/L |
| µmol/(min·L) | micromole per minute per liter |
| µmol/(h·L) | micromole per hour per liter |
| µmol/(h·mL) | micromole per hour per milliliter |
Diagnostic Uses
1. Organophosphate Poisoning
- Diagnostic
- Severity grading
- Serial monitoring
- RBC acetylcholinesterase may also be measured
2. Pre-anesthesia Screening
Identify pseudocholinesterase deficiency to avoid prolonged paralysis with succinylcholine.
3. Liver Function Assessment
Cholinesterase is a negative acute phase reactant & a marker of:
- Synthetic liver function
- Nutritional status
Low levels in:
- Cirrhosis
- Fulminant hepatitis
- Severe malnutrition
4. Occupational Monitoring
Chronic exposure in:
- Farmers
- Pesticide workers
- Industrial settings
5. Genetic Testing Adjunct
Dibucaine inhibition number:
- Low → atypical enzyme
- Normal → typical enzyme
Analytical Notes
- Serum is the preferred sample
- Hemolysis minimally affects results
- Assay methods:
- Colorimetric
- Rate reaction analysis
- IFCC standardized enzymatic protocols
- Colorimetric
- Serial values more important than one reading
- Avoid anticholinesterase drugs for accurate testing
Clinical Pearls
- Markedly low cholinesterase strongly suggests organophosphate poisoning.
- Pseudocholinesterase deficiency must be identified before anesthesia to prevent prolonged paralysis.
- Cholinesterase is a better liver function marker than albumin in rapid-onset liver failure.
- Normal cholinesterase does not rule out organophosphate poisoning; always check RBC acetylcholinesterase.
Interesting Fact
Cholinesterase was historically used to detect exposure to nerve agents (sarin, VX) because these agents irreversibly inhibit the enzyme — the same mechanism as organophosphate pesticides.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Enzymes.
- IFCC Enzyme Activity Standards.
- Mayo Clinic Laboratories - Cholinesterase.
- ARUP Consult - Toxicology & Pesticide Exposure.
- CDC Organophosphate Poisoning Clinical Guidelines.