A descriptive cross-sectional study using a community-based convenience sample of 100 healthy non-farmer volunteers (male:female = 1:1) was done at Anuradhapura during the month of September 2017. Anuradhapura is a district of North Central Province, Sri Lanka, where the majority belong to the rural sector (94.1%) [
9] and agriculture (55%) is its main employment [
10]. In 2014, the Sri Lankan government implemented a ban on three AChEIIs (chlorpyrifos, carbofuran, carbaryl) in Anuradhapura, as a response to increased toxicity [
11]. Further, two other AChEIIs (dimethoate, fenthion) were banned from the country during the same year.
Inclusion criteria of the study were Buddhists aged ≥ 18 years and ≤ 65 years, estimated glomerular filtration rate (eGFR) ≥ 60 ml/min/1.73m
2 according to CKD-EPI equation and permanent residence of Anuradhapura for ≥ 5 years. Exclusion criteria were any acute illness, history of acute organophosphate/carbamate poisoning, history of farming, history of use of acetylcholinesterase inhibitor medications, history of renal failure, malignancy, immunosuppression, haemoglobinopathies or anaemia, every day smokers [
12], heavy alcohol users [
13] and pregnancy.
The study was carried out to obtain demographic data, anthropometric measurements, blood pressure measurement and blood samples for eGFR and RBC-AChE activity. Study description, obtaining written informed consent, data collection and relevant physical examination were done by the first author. All necessary measures were taken to preserve participant’s privacy and confidentiality. Duplicate measurements of RBC-AChE activity in whole blood per haemoglobin concentrate was performed at the Department of Biochemistry, Faculty of Medicine and Allied Sciences, Rajarata University of Sri Lanka, according to the modified Ellman procedure [
14,
15]. Sigma-Aldrich reagents, USA [
16] were used as recommended, and the quality control was done using the AChE-check-control (high/low) from Securetec Detektions-Systeme AG, Germany [
17]. Spectrophotometric reading was done using Spectro 2000, Labomed, Inc., USA [
18]. Wavelengths of 546 and 436 nm were used for the measurement of haemoglobin content and RBC-AChE activity respectively. The measurement of RBC-AChE activity was done at a pH of 7.4 and at a temperature of 37 °C. The concentration in solution of Ellman’s reagent, ethopropazine hydrochloride and acetylthiocholine iodide were 10, 6 and 28.4 mM respectively [
14,
15]. Data was entered to a Microsoft Excel sheet (Additional file
1). Measures of central tendency and variation of RBC-AChE activity were described. Two-sample
T test was performed to determine significant difference in the means of RBC-AChE activity between males and females (
p < 0.05). Pearson’s correlation was sort for RBC-AChE activity against age, years residing at Anuradhapura, waist circumference, weight, height, body mass index (BMI), mean arterial pressure (MAP) and eGFR. Regression analysis was done to determine the strength of the relationship between RBC-AChE activity and its above-mentioned possible determinants.