Improved determination of acetylcholinesterase activity in human whole blood

Determination of erythrocyte acetylcholinesterase (AChE) activity is the ap propriate tool for the diagnosis of organophosphate exposure and intoxicati on. The original colorimetric Ellman procedure is disturbed by a high hemog lobin absorption at 412 nm. In our modified method the wavelength was chang ed to 436 nm. This reduced the indicator absorption to 80% and the hemoglob in absorption to 25%. The signal-to-noise ratio was further enhanced by red uction of pH and substrate concentration, thus making it possible to measur e 3% residual activity. AChE activity was determined in whole blood samples in the presence of the selective butyrylcholinesterase inhibitor ethopropa zine. Dilution of blood samples (1:100) stops secondary reactions in the pr esence of inhibitor (organophosphate) and reactivator (oxime). Normalizatio n of the AChE activity to the hemoglobin content, determined as cyanmethemo globin, prevented dilution errors. This modified approach provides a simple way for sensitive and precise determination of AChE activity in whole bloo d in the presence of organophosphates even with low-tech equipment. (C) 199 9 Elsevier Science B.V. All rights reserved.