Urine Carbamate Determination Compared with Plasma Pseudocholinesterase for Diagnosis of Insecticides Poisoning

Abstract

Introduction: Diagnosis of carbamate poisoning is frequently missed especially when patients present after the recovery of pseudocholinesterase inhibition. Confusion is due to the similarity of the clinical picture with that of food poisoning and other infectious syndromes. Patients and methods: Patients (n=40) admitted within 4 hours of carbamate intoxication were included in the study. They were graded according to Poison severity score PSS. Normal volunteers (n=10) were included and served as negative control group. Normal subjects and all patients were tested for plasma pseudocholinesterase (PsChE) within 4 hours and 18 hours from carbamates exposure. Urine carbamate concentration was determined on the 18 th hour and 2 days after exposure. Different PSS groups and normal volunteers were compared for their plasma PsChE and urine carbamate levels using student t test and correlation coefficient Method used for PsChE determination is the kinetic assay method. Urine carbamate concentrations were determined by spectrophotometry using modification of the method of Tamrakar. Carbamate determination method was tested for linearity, precision, recovery and limit of detection of the carbamates Results: PsChE was significantly lower in PSS II compared to PSS I. No significant difference in PsChE was noticed between both patient's groups and normal volunteers on the 18 th hour from carbamate exposure. Urine carbamate concentration was significantly higher in PSS II compared to PSS I on the 18 th hour and 2 days after exposure. No correlation was detected between the maximum urine carbamate concentration and plasma pseudocholinesterase. The method specificity increased after modification from 76.9 to 91%. Recovery ranged between 95 and 98%. Limit of detection is 0.1µg/ml and limit of quantification is 0.2µg/ml. The technique is highly reproducible with inter-day precision RSD less than 8%. Conclusion: A better evaluation and diagnosis of carbamate poisoning patients with delayed presentation can be achieved using urine carbamate determination rather than plasma pseudocholinesterase which is often normalized at the time of presentation