[Tests of micronucleus count in lymphocytes: a validation study].

In spite of the development of new automated methods proposed for scoring of micronuclei, manual analysis of micronucleated cells by light microscopy is still largely employed. The purpose of this study was to define the minimal number of mononucleated and binucleated cells representative of the total number of cells of the side, to determine the division rate. The second aim was to define the minimal number of binucleated cells representative of the total number of the binucleated cells on the same slide, to determine the rate of binucleated micronucleated cells. Total mononucleated, binucleated and polynucleated cells were scored in each slide for determining the 'theoretical division rate'. Among total binucleated lymphocytes observed in each slide, micronucleated cells containing one, two or more micronuclei were scored to determine the 'theoretical micronuclei rate'. Then, 'experimental division rates' were calculated by dividing microscope slides into random areas of 500 lymphocytes, and recording mononucleated, binucleated cells. 'Experimental micronuclei rates' were determined by dividing microscope slides into random areas of 500 binucleated cells, and recording micronucleated cells containing one or more micronuclei. 'Experimental division rates' obtained by examining sets of 4000 cells were shown to be not representative of the corresponding 'theoretical rate' (statistical difference by the chi-squared test, p < 0.05)). 'Experimental micronuclei rates' obtained by examining sets of 500 binucleated cells were shown to be representative of the corresponding 'theoretical micronuclei rate' (no statistical difference by the chi-squared test, p > 0.05).