What is the blood test for pseudocholinesterase deficiency?

Blood Testing for Pseudocholinesterase Deficiency

The blood test for pseudocholinesterase deficiency consists of two components: measurement of serum pseudocholinesterase (butyrylcholinesterase) enzyme activity level and the dibucaine inhibition test to determine the genetic variant. 1

Primary Diagnostic Tests

Serum Pseudocholinesterase Activity Level

• Quantitative enzyme activity measurement is performed on a blood sample to determine the absolute level of pseudocholinesterase enzyme 1
• Normal reference range is typically 2673-6592 IU/L 1
• Deficient individuals show markedly reduced activity (e.g., 552-789 IU/L in documented cases) 1
• This test identifies whether enzyme deficiency exists but does not determine the genetic cause 2

Dibucaine Inhibition Test (Dibucaine Number)

• This is the critical second test that distinguishes genetic variants from acquired deficiency 1, 2
• Measures the percentage inhibition of enzyme activity by dibucaine 1
• Normal dibucaine number: 81.6-88.3% 1
• Abnormal results (e.g., 61.1%) indicate a pharmacogenetic basis for the deficiency 1
• This test identifies specific genetic variants that cause altered enzyme structure 2

Additional Confirmatory Tests

Fluoride Inhibition Test

• Provides complementary information about enzyme variants 2, 3
• The fluoride number should be within normal range in certain variant types 3
• Used alongside dibucaine testing for complete phenotype characterization 2

Immunoreactive Protein Measurement

• Measures the amount of enzyme protein present versus its activity 3
• In silent type II variants, immunoreactive substance may be normal or elevated despite low activity 3
• Helps distinguish between absent enzyme production versus production of dysfunctional enzyme 3

Clinical Context and Timing

When to order these tests:

• Following unexpectedly prolonged paralysis after succinylcholine or mivacurium administration (typically >30 minutes for procedures lasting <20 minutes) 4, 1
• The initial enzyme level should be drawn during or shortly after the prolonged paralysis event 1
• A repeat test 6 months later with dibucaine inhibition confirms hereditary deficiency and rules out transient acquired causes 1

Important Caveats

Ratio Analysis for Heterozygotes

• The ratio of cholinesterase activity to serum albumin concentration is more sensitive than enzyme activity alone for detecting heterozygous carriers 3
• This is particularly useful in family screening after an index case is identified 3

Limitations of Traditional Testing

• Standard enzyme activity, dibucaine, and fluoride tests are inadequate for identifying all variants 2
• Some cases of prolonged succinylcholine response remain unexplained by these traditional methods 2
• Molecular genetic testing can identify previously unrecognized variants when traditional tests are inconclusive 2

Acquired vs. Genetic Deficiency

• Multiple acquired conditions can reduce enzyme activity (liver disease, malnutrition, pregnancy, certain medications) 5
• The dibucaine inhibition test is essential to distinguish pharmacogenetic deficiency from acquired causes 1
• Normal dibucaine and fluoride numbers with low enzyme activity suggest acquired deficiency rather than genetic variants 3