>Craig,
>
>You may be dealing with a case of antbody interfererence, possibly anti-T4,
>anti-T3 antibodies that are more prevalent in autoimmune thyroid disease,
>although results are usually falsely elvated Suggest getting TFT assays
>checked by another sytem. I also would measure the SHBG level as it is a
>sensitive peripheral marker of thyroid hormone activity and levels are
>usually 2-3 times raised in hyperthyroidism.(we would be happy to measure
>this for you),
>
>Regards,
>
>Roy Fisher,
>Royal Cornwall 01872 252546
>-----Original Message-----
>From: Craig Webster <[log in to unmask]>
>To: Acb-Clin-Chem-Gen <[log in to unmask]>
>Date: 18 November 1998 10:44
>Subject: ? Thyrotoxicosis
>
>
>>We have a patient with some signs of thyrotoxicosis
>>
>>Lid retraction
>>Weight loss
>>
>>However his thyroid function results are as follows (typical example)
>>
>>Total T4 70
>>Free T4 19.5
>>TSH < 0.03
This correspondence illustrates the problems of reporting/discussing assay
results without stating the methodology used. All total T4 and T3 - and
more particularly FT4 and FT3 - assay results are method dependent, even
more particularly if T4/T3 autoantibodies are present.
Moreover, it is highly questionable whether - if antibodies are indeed
present - any thyroid tests are diagnostically relevant, since the rates of
T4/T3 release from such antibodies are likely to be entirely different from
those governing the hormones'release from TBG, albumin and TBPA. In these
circumstances, the free hormone hypothesis may be invalid, and neither
total hormone concentrations nor free hormone concentrations measured under
equilibrium conditions in vitro will be indicative of thyroid hormone
availability to peripheral tissues
Roger Ekins
UCL
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