REPEATABILITY AND VALIDITY OF A FIELD KIT FOR ESTIMATION OF CHOLINESTERASE IN WHOLE-BLOOD

Objectives-To evaluate a spectrophotometric field kit (Test-Mate-OF) f or repeatability and validity in comparison with reference laboratory methods and to model its anticipated sensitivity and specificity based on these findings. Methods-76 farm workers between the age of 20 and 55, of whom 30 were pesticide applicators exposed to a range of organo phosphates the preceding 10 days, had taken for plasma cholinesterase (PCE) and erythrocyte cholinesterase (ECE) measurement by field kit or laboratory methods. Paired blinded duplicate samples were taken from subgroups in the sample to assess repeatability of laboratory and fiel d kit methods. Field kits were also used to test venous blood in one s ubgroup. The variance obtained for the field kit tests was then applie d to two hypothetical scenarios that used published action guidelines to model the kit's sensitivity and specificity. Results-Repeatability for FCE was much poorer and for ECE slightly poorer than that of labor atory measures. A substantial upward bias for field kit ECE relative t o laboratory measurements was found. Sensitivity of the kit to a 40% d rop in FCE was 67%, whereas that for ECE was 89%. Specificity of the k it with no change in mean of the population was 100% for ECE and 91% f or PCE. Conclusion-Field kit ECE estimation seems to be sufficiently r epeatable for surveillance activities, whereas PCE does not. Repeatabi lity of both tests seems to be too low for use in epidemiological dose -response investigations. Further research is indicated to characteris e the upward bias in ECE estimation on the kit.