Re: Blood bioassay

[stabin@esper.com (Mike Stabin)]

Ron Kathren wrote:

>Re the question posed by Ed Kaplan at Brookhaven re using blood for routine
>Pu bioassay.
>
>Clearly, if the basis for the biokinetic models is correct, the blood is
>representative of what is in the systemic pool -- ie the systemic
>deposition.  Obviously, blood levels would be affected by chelation, but
>assuming no chelation, blood shouyld be a very good indicator of systemic
>deposition if the time after intake is known.  While not fully relevant to
>the question asked, the most extensively studied human case was the Hanford
>Am case, who was heavily chelated and showed a power function decrease in
>blood levels of Am.  However, I would likely vote against a routine blood
>sample for Pu assessment since the proicedure is invasive and, because of
>the low levels of Pu in blood, I suspect a relatively large sample would be
>required.  If it could be done with a finger stick, the picture changes.
>But in any case, data are needed to support the use of blood sampling, and a
>carefully constructed experimental protocol would have to be worked out.
>

In general, I would not consider blood to be of much use in this regard, for
the reasons that Ron mentions - the biokinetic model.  For
radiopharmaceuticals, one generally observes a very fast clearance from
blood, with later exchange back from some of the organs of uptake on the way
to excretion.  Even in a good recycling-based model, predicting the time
behavior of this process is tenuous on a subject-specific basis.  Given that
the ICRP models are also non-recycling, I would consider the predicted
activity in the "transfer compartment" to be of little use in making
concrete predictions based on sample measurements, not to mention detection
limit problems, as Ron alluded to.

Mike Stabin
Oak Ridge