Cholinesterase

5 mL blood in lithium heparin tube.

Spectrophotometry, with measurement of total activity, Dibucaine-resistant activity and fluoride-resistant activity.

Dibucaine and fluoride numbers correspond to the percentage inhibition of cholinesterase in the presence of the inhibitor.

Genotyping is available for the identification of some mutations.

See Molecular genetics.

Consult pathologist.

Prolonged apnoea following suxamethonium (Scoline) or mivacurium.

For organophosphate and carbamate poisoning, see Cholinesterase red cell, which is the preferred test.

Susceptibility to 'Scoline apnoea' is inherited as an autosomal recessive disorder; cholinesterase activity is usually, but not always, low.

Dibucaine and fluoride numbers improve the sensitivity and specificity of the test.

Family studies should be done so that other affected individuals can be cautioned against exposure to suxamethonium or mivacurium. Genotyping can clarify risk.

Low levels are also found in pregnancy and in patients with hepatocellular disease.

Organophosphate poisoning temporarily reduces the activity of this enzyme, making it useful for the detection of repeated acute poisoning.