A prospective study on effect of periodic health examination for prevention of chronic diseases

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Two cohorts of a community population and a working poplation have been organized to evaluate effectiveness of periodic health examination for primary and secondary prevention of chronic diseases. The member of the community cohort was selected from those who attended periodic health examinations offered by the Health Care Program for Senior Person in 1989 and/or 1990 and submitted written agreement to become a member of the cohort. Workers of municipalities in a prefecture composed the worker's cohort. A total of 22, 478 workers who belong one of 118 municipalities are offered periodic health examination under a same program. Analysis is done to clarify 1)effectiveness of each test of the examination for early detection of disease and 2)effectiveness of the examination from aspect of health education and program management. For the first analysis, a survey of incidence for average of 117 days after an examination of the community cohort revealed 47% of the member visited medical facilities at least once during the period. Only 15% of them were detected by the examination. Based on the results, a mathematical model was created to estimate detectable proportion of a subclinical disease when a screening test is applied to a given population. Introduced variables for the model are interval of the examination, length of subclinical stage, specificity and sensitivity of the test. Positive predictive values of the tests are estimated for the occupational cohort. The range of estimated values distributed rather widely from 20% to 96'/. . A detailed survey on diabetes mellitus revealed 379 positive cases on fasting blood sugar test among 6920 workers who have no history of diabetes. Amonly this positive group only 126 visited physicians during one year after the examination. A postexamination questionnaire survey of the community cohort proved a substantial improvement in life style if it is compared to the preexamination.