Pseudocholinesterase Phenotype interpretation is based on the enzyme activity and the dibucaine number (which measures enzyme inhibition by dibucaine). Patients with abnormal phenotypes cannot break down succinylcholine or mivacurium at the normal rate, resulting in prolonged paralysis with these drugs. Pseudocholinesterase genotyping can confirm the phenotype and may add additional information.
There are several phenotypes, each of which is associated with a different risk for prolonged paralysis following the administration of succinylcholine or mivacurium. Decreased enzyme activity in conjunction with dibucaine number less than 30 suggests high risk for prolonged paralysis. Normal to decreased enzyme activity in conjunction with a dibucaine number 30-79 suggests variable risk. Decreased enzyme activity in conjunction with dibucaine number greater than 80 suggests variable risk, but these results may also be caused by organophosphates, liver disease, pregnancy, or residual circulating succinylcholine. Specimens should be collected at least 48 hours after the administration of succinylcholine or mivacurium.
Patients with acute or chronic liver
disease, organophosphate poisoning, chronic renal disease, in late stages of
pregnancy, or on estrogen therapy may have markedly decreased PChE
activities.
PSEUDOCHOLINESTERASE PHENOTYPES
U: Homozygote Usual (normal), frequency = 96%: No increased risk for prolonged paralysis.
UA: Heterozygote Usual/Atypical, frequency = 3%: Low risk for prolonged paralysis. Risk of prolonged paralysis is higher with a large dose and short surgery.
A: Homozygote Atypical, frequency 1 in 3,000: Very high risk (100%) for prolonged paralysis.
US: Heterozygote Usual/Silent, frequency = 0.7%: Low risk for prolonged paralysis. Risk of prolonged paralysis is higher with a large dose and short surgery.
S: Homozygote Silent, frequency 1 in 40,000: Very high risk (100%) for prolonged paralysis. This patient could be phenotype "U" with concomitant organophosphate poisoning.
AS: Heterozygote Atypical/Silent, frequency 1 in 8,000: Very high risk (100%) for prolonged paralysis.
FS: Heterozygotes Fluoride Sensitive/Silent, frequency rare: High risk for prolonged paralysis. Risk is higher with large dose and short surgery.
AF: Heterozygote, Atypical/Fluoride Sensitive, frequency rare: High risk for prolonged paralysis. Risk is higher with large dose and short surgery.
UF: Heterozygotes Usual/Fluoride Sensitive, frequency rare: Low risk for prolonged paralysis. Risk of prolonged paralysis is higher with a large dose and short surgery.
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427