At present we measure TSH alone as an initial test for thyroid dysfunction
in patients not on treatment. If this is below the reference interval we
cascade onto fT4 and then onto fT3 if this is >18pmol/L. We also do fT3 on
lower levels of fT4 if the clinical information suggests hyperthyroidism is
to be excluded. In short, much more emphasis is placed on the fT3 (which
rises earlier and proportionately higher in hyperthyroidism) than fT4.
I know this may sound heretical to some (mainly because of analytical
considerations), but is there any point in measuring the fT4 in this
situation? Should we not just cascade from low TSH directly to fT3 (which
costs the same as fT4) and be done with it?
I would be interested to here peoples comments or from anyone with
experience of such a cascade system.
Dr. Eric S. Kilpatrick
Consultant in Chemical Pathology
Department of Clinical Biochemistry
Hull Royal Infirmary
Anlaby Road
Hull HU3 2JZ
Tel 01482-674312
Fax 01482-674310
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