Aside from the questions and subsequent debate regarding desirability of
seeking the advice from the Guys posons unit, I was amused by the
following section of Avril Owen's message:
>Guy's were phoned for a second time on day 3, and the was told to 'ask the
>lab to dilute the sample so that an accurate result for fT4 could be
>obtained'.
It is perhaps understandable that a consultant paediatrician does not know
that diluting a sample neither significantly alters the FT4 concentration,
nor enables a more accurate FT4 result to be obtained. But my recent
experience as an advisor to a committee set up by the NCCLS set up to "
address existing problems in nomenclature and in measurement of free
(non-protein bound) hormones in blood.." (see
http://www.nccls.org/projects.htm ) indicates that misunderstanding of this
issue may be more common than one would hope. The first draft of a
document produced by this committee suggests that 'most free hormone
immunoassays (sic) do not recommend dilution of samples to bring them
within the dynamic range of the assay', the authors of this section
implying that some kit manufacturers (?) do, and that it is legitimate to
do so. I'm sure that this suggestion will not be permitted to remain in the
final document, but that it has voiced at all indicates that
misconceptions regarding free hormone measurement continue to be widespread.
Roger Ekins
University College London
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