Cholinesterase is an enzyme present in plasma and synthesized by
the liver. Its true physiological function is unknown, so its function may
be to hydrolyze choline in plasma. Cholinesterase activity is usually
measured for liver function, is a sensitive test of exposure to
pesticides organophosphorus and identification of patients with the
atypical form of enzyme whose presents high sensitivity to succinylcholine.
The dibucaine percent inhibition is determined in addition to total
activity cholinesterase to detect the presence of an abnormal genetic
variant of cholinesterase1,5,6.
Clinical diagnosis should not be made on a single test result; it should
integrate clinical and other laboratory data.
PREPARATION
Working reagent (WR):
Dissolve ( ) one tablet of R 2 Substrate in one vial of R 1.
Cap vial and mix gently to dissolve contents.
Inhibition (WR-I):
Add 300 L of R 3 Inhibitor to working reagent (WR).
Stability: 2 hours at 2-8ºC.
STORAGE AND STABILITY
All the components of the kit are stable until the expiration date on the
label when stored tightly closed at 2-8ºC, protected from light and
contaminations prevented during their use.
Do not use the tablets if appears broken.
Do not use reagents over the expiration date.
Signs of reagent deterioration:
- Presence of particles and turbidity.
- Blank absorbance (A) at 405 nm 0.70.
ADDITIONAL EQUIPMENT
- Spectrophotometer or colorimeter measuring at 405 nm.
- Thermostatic bath at 25ºC, 30ºC o 37ºC ( 0.1ºC)
- Matched cuvettes 1.0 cm light path.
- General laboratory equipment (Note 1).
SAMPLES
Serum or heparinized plasma1
: Stability 7 days at 2-8ºC.
QUALITY CONTROL
Control sera are recommended to monitor the performance of assay procedures:
SPINTROL H Normal and Pathologic (Ref. 1002120 and 1002210).
If control values are found outside the defined range, check the instrument,
reagents and technique for problems.
Each laboratory should establish its own Quality Control scheme and corrective
actions if controls do not meet the acceptable tolerances.
REFERENCE VALUES1,2
Percent inhibition of cholinesterase activity by dibucaine:
Normal 70-90% Heterozygotes 30-70% Homozygotes 0-20%
These values are for orientation purpose; each laboratory should establish its
own reference range.
PERFORMANCE CHARACTERISTICS
Measuring range: Up to linearity limit of 0.250 A/30 s.
If the results obtained were greater than linearity limit, dilute the sample 1/2 with
NaCl 9 g/L and multiply the result by 2.
Accuracy: Results obtained using SPINREACT reagents (y) did not show
systematic differences when compared with other commercial reagents (x).
The results of the performance characteristics depend on the analyzer used.
INTERFERENCES
Moderate hemolytic will not interfere in the results1,2. A list of drugs and other
interfering substances with cholinesterase determination has been reported by
Young et. al3,4.
NOTES
1. Use glass containers only. Inhibitors may be extracted from some plastics.
2. SPINREACT has instruction sheets for several automatic analyzers.
Instructions for many of them are available on request.
