[A longitudinal study of specific gravities of whole blood in dyestuff plant workers]

Specific gravities of whole blood (GB) have been used widely as a screening test of anemia in industrial surveillance systems in Japan. The recent spread of electronic computers enables us to make effective use of a large quantity of information and GB could be used to screen examinees more accurately if the various factors which can bring about fluctuations in GB or the data obtained through past health examinations are taken into consideration. Time trends of GB can be explained by the combination of the physiological effect of aging, environmental factors such as diet or working conditions, and the birth cohort effect. The present study was aimed to identify the factors which bring about fluctuations in GB through longitudinal as well as cross-sectional observations. The study subjects consisted of 1,105 male workers engaged in dyestuff production work or clerical work at a dyestuff plant located in Tokyo during the period from 1953 to 1976. Though a negative association was found between GB and the age of workers through cross-sectional observations, it was found through longitudinal observations that the individual GB had a tendency to rise during the period in each birth cohort. These facts suggest that some environmental factors acted so as to raise the individual GB during this period in opposition to the physiological effect of aging to lower it. In order to evaluate the associations of educational history, working conditions, age and physique of workers with GB, information on these factors obtained through health examinations in 1960, 1965, 1970 and 1975 was analyzed separately by the multi-dimensional contingency table method. As a result, it was demonstrated that GB was directly related to all of these factors in 1960 and 1965, to age and physique in 1970 and only to age in 1975. These results suggest that environmental factors associated with educational history or working conditions played a greater part in the earlier periods when the average GB was not as high as in the later periods. In summary, the efficiency of GB as a screening test will be considerably improved if the judgment criteria utilize information about these environmental factors as well as the physiological effect of aging based on the information obtained from this study.