The paper presents the exposure assessment method and quality control procedure used in an international, multi-centre case-control study within a joint Nordic and Italian cohort. This study was conducted to evaluate whether occupational exposure to carcinogens influenced the predictivity of high frequency of chromosomal aberrations (CA) in peripheral lymphocytes for increased cancer risk. Occupational hygienists assessed exposures in each participating country: Denmark, Finland, Italy, Norway and Sweden. The exposure status to a carcinogen or a clastogen was coded in the cohort according to the original CA studies at the time of CA testing, but not for the whole work life. An independent occupational hygienist coordinated harmonization of the assessment criteria and the quality control procedure. The reliability of the exposure assessments was calculated as deviation from the majority of the assessors, as Cohen's kappa and as overall proportion of the agreements. The reassessment of the exposures changed the exposure statuses significantly, when compared with the original cohort. Harmonization of the exposure criteria increased the conformity of the assessments. The prevalence of exposure was higher among the original assessors (the assessor from the same country as the subject) than the average prevalence assessed by the other four in the quality control round. The original assessors classified more job situations as exposed than the others. Several reasons for this are plausible: real country-specific differences, differences in information available to the home assessor and the others and misunderstandings or difficulties in translation of information. To ensure the consistency of exposure assessments in international retrospective case-control studies it is important to have a well-planned study protocol. Due to country-specific environments a hygienist from each participating country is necessary. A quality control study is recommended, to be performed as described, combined with round-table meetings to minimize information bias between the assessors.
Keywords: Carcinogens; Case-Control Studies; Chromosome Aberrations; Chromosome Disorders; Epidemiologic Methods; Female; Humans; International Cooperation; Leukocytes, Mononuclear; Male; Occupational Exposure; Quality Control; Reproducibility of Results; Retrospective Studies; Risk Assessment; Risk Factors