Laboratory Studies
Pseudocholinesterase deficiency is diagnosed by plasma assays of pseudocholinesterase enzyme activity. A sample of the patient's plasma is incubated with the substrate butyrylthiocholine, along with the indicator chemical 5,5'-dithiobis-(2-nitrobenzoic acid), which produces a colored product that is assayed by spectrophotometry. The resulting amount of spectrophotometric absorption is proportionate to the pseudocholinesterase enzyme activity that is present in the patient's plasma sample. [12, 18]
Because succinylcholine metabolites can interfere with this assay, plasma samples should be collected after muscle paralysis has completely resolved. Dibucaine and fluoride numbers can be determined by repeating this assay in the presence of standard aliquots of either dibucaine (0.03 mmol/L) or fluoride (4 mmol/L) in the reaction mixture to determine the percentage inhibition of enzyme activity caused by these agents.
A simplified screening test of pseudocholinesterase enzyme activity can be performed using the Acholest Test Paper (see Table 2, below). When a drop of the patient's plasma is applied to the substrate-impregnated test paper, a colorimetric reaction occurs. The time it takes the exposed Acholest Test Paper to turn from green to yellow is inversely proportionate to pseudocholinesterase enzyme activity in the plasma sample.
Table 2. Reaction Times for Acholest Test Paper (Open Table in a new window)
Reaction Time |
Pseudocholinesterase Enzyme Activity |
< 5 min |
Above normal |
5-20 min |
Normal |
20-30 min |
Borderline low |
>30 min |
Below normal |
The complete DNA sequence and amino acid structure of both the normal pseudocholinesterase protein and most of its abnormal variants have now been identified. However, molecular genetic techniques such as polymerase chain reaction (PCR) amplification with allele-specific oligonucleotide probes for identifying abnormal pseudocholinesterase genotypes are currently available only in a limited number of research laboratories and are not yet available for routine clinical use.
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Noninvasive ventilation. A bilevel positive airway pressure (BIPAP) prototype is shown here. Expiratory positive airway pressure is the expiratory pressure setting that determines the amount of positive end-expiratory pressure that is applied. The inspiratory positive airway pressure setting is the pressure support. The device can be used in spontaneous mode or timed mode (with a mandatory backup respiratory frequency).
Tables
Ea |
Atypical dibucaine-resistant variant |
Point mutation |
Ef |
Fluoride-resistant variant |
Point mutation |
Es |
Silent variant |
Frameshift mutation |
*These alleles may occur either in the homozygous form or in any heterozygous combination with each other, with the normal Eu allele, or with a number of additional rare variant abnormal alleles. |
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Reaction Time |
Pseudocholinesterase Enzyme Activity |
< 5 min |
Above normal |
5-20 min |
Normal |
20-30 min |
Borderline low |
>30 min |
Below normal |
