What this test measures
There are two cholinesterases — acetylcholinesterase (red cell / nerve junction) and pseudocholinesterase (butyrylcholinesterase, BuChE, made in the liver and present in serum). The serum test measures pseudocholinesterase. It is inhibited by organophosphate and carbamate insecticides, which are very common causes of poisoning in rural India.
The enzyme is also responsible for breaking down some short-acting muscle relaxants used in anaesthesia (suxamethonium / succinylcholine, mivacurium). Genetic deficiency causes prolonged paralysis after these drugs.
Why it matters
In India, organophosphate poisoning — accidental, occupational and self-harm — is a major cause of emergency admissions and remains a significant cause of mortality. Serum cholinesterase falls within hours of exposure and stays low for weeks; it confirms the diagnosis, guides atropine and pralidoxime therapy, and tracks recovery.
The test is also used pre-anaesthesia to screen for pseudocholinesterase deficiency (suxamethonium apnoea — prolonged paralysis after succinylcholine) in patients with a personal or family history of unexplained prolonged paralysis, and to detect chronic exposure in agricultural workers handling pesticides.
How to prepare
No fasting required. Mention any recent pesticide exposure (occupational, accidental, intentional), recent anaesthesia with suxamethonium / mivacurium, family history of suxamethonium apnoea, and all medications. For acute organophosphate poisoning, do not delay treatment for the result — clinical diagnosis comes first.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Pseudocholinesterase (U/L)[1][2] | 5320 – 12,920 (method-dependent — confirm with lab) | Low pseudocholinesterase — organophosphate / carbamate poisoning (the major use), inherited deficiency (suxamethonium sensitivity), chronic liver disease (the enzyme is made in the liver), severe malnutrition / hypoalbuminaemia, late pregnancy, oral contraceptives, severe burns. Acute poisoning — values fall by 50–100% and recover over weeks (red cell acetylcholinesterase takes 3–4 months). | High pseudocholinesterase — usually no clinical significance. Can be seen in obesity, type IV hyperlipoproteinaemia, and (rarely) some genetic variants. |
Cholinesterase in clinical practice
| Scenario | Expected pattern | Action |
|---|---|---|
| Acute organophosphate poisoning | Pseudocholinesterase very low (often <30% of baseline) | Atropine + pralidoxime; supportive care |
| Carbamate poisoning | Mild–moderate fall; recovers faster (reversible inhibition) | Atropine; pralidoxime NOT used |
| Pre-anaesthesia screen | Low values predict prolonged paralysis with suxamethonium | Use alternative muscle relaxant |
| Chronic liver disease | Persistently low; tracks liver synthetic function | Treat underlying liver disease |
| Suspected chronic pesticide exposure (farmers) | Persistently low across exposed workers | Occupational health intervention |
Frequently asked questions
Why does this test matter in pesticide poisoning?
Organophosphate and carbamate pesticides bind cholinesterase, allowing acetylcholine to accumulate and cause the cholinergic toxidrome (salivation, urination, lacrimation, sweating, bradycardia, muscle fasciculation, seizures). Serum cholinesterase falls quickly and confirms the diagnosis. Treatment with atropine and pralidoxime must not wait for the result in a clinically obvious case.
Do I need to fast?
No fasting required.
What is suxamethonium apnoea?
A genetic deficiency of pseudocholinesterase. Affected patients break down suxamethonium very slowly, resulting in prolonged paralysis (1–6 hours instead of 5–10 minutes) after a routine dose. Pre-operative testing in family members of affected patients can prevent surprises.
How long does cholinesterase stay low after organophosphate exposure?
Serum (pseudo) cholinesterase recovers in 4–6 weeks. Red cell acetylcholinesterase takes 3–4 months to fully recover — it is the more accurate marker of true synaptic enzyme activity but is less widely measured.
Is the test useful in farmers with chronic pesticide exposure?
Yes — serial measurements in agricultural workers can detect chronic low-level toxicity before symptoms develop and trigger workplace safety changes.
Can liver disease affect cholinesterase?
Yes — the liver synthesises the enzyme. Severe chronic liver disease and cirrhosis cause persistently low values, which reflect liver synthetic function.
Are there drugs that lower cholinesterase?
Yes — oestrogens (oral contraceptives, pregnancy), some chemotherapy, and exposure to organophosphates / carbamates. Mention all medications when interpreting an unexpectedly low value.
Related Other / Biochemistry tests
Tests commonly ordered alongside CHOLINESTERASE, or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Cholinesterase Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Pseudocholinesterase Deficiency · accessed 2026-05-30T00:00:00.000Z
- WHO — Organophosphate Poisoning Management · accessed 2026-05-30T00:00:00.000Z
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