Pseudocholinesterase Deficiency Workup

Updated: Nov 14, 2017
  • Author: Daniel R Alexander, MD; Chief Editor: Karl S Roth, MD  more...
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Workup

Laboratory Studies

Diagnosis of pseudocholinesterase deficiency is made 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 will produce a colored product that is assayed using spectrophotometry. The resulting amount of spectrophotometric absorption is proportionate to the pseudocholinesterase enzyme activity that is present in the patient's plasma sample. [9, 13]

Because succinylcholine metabolites can interfere with this assay, plasma samples should be collected after muscle paralysis has completely resolved. The 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 percent 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 proportional to the 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 in routine clinical use.