Reference the following manuscript.  Here we compare the classical approach of using washed, red blood cell membranes + plasma, and a direct measurement of ChE in the blood following the removal of hemoglobin (as hemoglobin interferes with the assay due to spectral overlap).  The manuscript is McGarry et al. 2013 - Evaluation of HemogloBind Treatment for preparation of samples for cholinesterase analysis.  I hope this helps.  Ellman et al (1961) is the original paper describing the method and that will help you as well.

Thank you all for your answers.

Dear Raphael, I used this one below described, if you need other information, contact to me

Cholinesterase (CHE) MTP assay

Reagents

R1: dissolve in 800 ml dH2O, 91.5 mM pyrophosphate, 2.44 mM K-hexacyanoferrate (III) and adjust pH to 7.7 with 1 M citric acid and fill up to 1 liter with dH2O; R2: dissolve in 800 ml dH2O, 10 mM HEPPS, 45.7 mM Butyrylthiocholine iodide, and adjust pH to 4.0 with o-phosphoric acid, add between 0.25% DMSO, ad fill up to 1 liter with dH2O. Store both reagents in amber glass bottle at 2 – 8 °C, protected from light, avoiding also contamination.

Procedure

Mix in two MTP wells 250 µl R1 and in one of two dispense 5 µl serum/plasma (sample), and another dispense 5 µl of 0.9% NaCl (blank) and pre-incubate for 60 sec. at 37 °C. Dispense 50 µl of R2 (at 37 °C) in both wells, and measure Abs to 405 nm, exactly 90, 120, 150 and 180 sec after addition of R2. Calculate the ΔAbs/min., subtract from this the Abs blank valute, and multiply for 21935 that is conversion factor

by mistake

conversion factor instead of 21935 is 65804

I apologize