CHAPTER 4 HEMATOLOGY 4.1 PREVIOUS FINDINGS Hematological determinations employed in the initial post-exposure period included total leukocyte, neutrophile, lymphocyte, and platelet counts and hematocrit determinations. Wheu- ever possible, an entire exposure group was studied in a single day. In order to estimate the severity of the hematological response, findings were comparable to a phase of a control group similar, where possible, with respect to race, age, sex, background, and habits. Depression of the total white, neutrophile, lymphccyte, and platelet counts was marked in the Rongelap group and less severe in the Allinginae group. The total white count was consist- ently lowest during the sixth and seventh post- exposure weeks, followed by an upward trend with levels remaining below that of the cortrol population at the end of the observation period. The drop in lymphocytes was early and profound, with little or no evidence uf recovery during the period of observation. Fluctuations in the total white count were due to changes in the neutrophile count. Neutrophile counts in 10 per cent of the Rongelap group fell to below 1000 cells/mm? at the time of maximum depression. Platelet counts showed iess fluctuation than did the total white and neutrophile counts and reached lowest values on the 30th post-irradiation day. At this time, counts in 20 per cent of the Rongelap group were belcw 90,000/mm’, A eecondary fall in platelets, with greatest depression on the 55th day, was observed, and recovery tc control levels was not complete at 6 months. 4.2 METHODS Determinations made on peripheral blood included total white, neutrophile, lymphocyte, and platelet counts, as well as hematocrit determinations. Techniques employed were identical with those used during the initial observation period.’ Two determinations were made on each individual approximately one week apart (date of all counts taken as the 185th post-irradiation day). In addition to peripheral blood, bone marrow from the anterior or posterior iliac crest was obtained on 21 « ‘posed and 20 control individuals. Approximately 1 ml was aspirated, and cover slip preparatious were made from the small particles of marrow thus obtained. Differential counts were taken on these preparations. Part of the marrow was allowed to clot ona glass slide and was then fixed in formalin-sublimate solution for later examination of histologi- cal structure and degree of cellularity. 4.3 PRESENT FINDINGS Peripheral blood count data for the exposed and control populations are given in Tabies 4.1 to 4.3, Figs. 4.1 to 4.4, and in Appendices A and B. To obtain valid comoarisons within 25