III.

A.

HEMATOLOGIC OBSERVATIONS*

Background

Since alterations in leukocyte and platelet counts are among the most

sensitive and reliable responses to radiation injury, careful hematologic
Monitoring of exposed populations was instituted immediately following the accident and has continued subsequently at frequent intervals.
All persons were
not always available for study during each field trip.
Accordingly, surveys
were often made on a semiannual or quarterly basis by the medical team or the
resident physician at Kwajalein with the objective of performing hematologic

evaluations of most exposed individuals at least annually.

This allowed

values for each person (as well as mean values for each exposure group) to be
followed serially in comparison with values for unexposed populations and with
each other over the course of time.
The prompt and significant depressions in leukocyte and platelet counts
observed in the combined Rongelap and Ailingnae groups immediately after the
accident, and the subsequent return to stable plateaus closely approximating
control mean values, are shown in Figure 1.
The severity of initial depresSions in cell counts varied among the three exposed groups, correlating reasonably well with that expected from the best estimates of their degrees of radiation exposure.
In the Rongelap grounv, these effects were moderately severe,
and it was thought that an additional increment of 50 to 100 rem probably

would have resulted in the sequelae of pancytopenia (infection and hemorrhage)
with the statistical possibility of death (2).
The early fluctuations in neutrophil and total leukocyte counts (Figure
la) apparently followed a burst of leukocytosis during the first few days and

might have reflected individual responses to other injuries, such as beta
burns, or to transient respiratory infections that occurred during the first
month. The response of peripheral lymphocytes (Figure lb) to the radiation injury was rapid and marked, whereas the platelets fell gradually to reach a
Nadir in about one month (Figure lc).
Recovery required approximately one
year for neutrophils and at least two years for lymphocytes and platelets.

It is notable that the mean peripheral blood counts recorded in

Figure 1, especially over the past 6 to 8 years, have shown less annual fluctuations for the combined Rongelap~Ailingnae groups than for the comparison

populations. This may reflect the more variable composition of the latter
occasioned by gradual attrition of the age- and sex-matched controls available
for followup studies and their replacement with individuals from other population groups, primarily unexposed Rongelap residents.

B.

Methods

Hematologic measurements for the first few years following the accident

were performed on capillary blood from the finger or occasionally from the

*This section was written by Drs. D.E. Paglia (UCLA) and E.P. Cronkite (BNL),
with the technical assistance of Mr. W.

Scott

-16-

(BNL).

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