[Free thyroxine in routine diagnosis]

In our hospital the measurement of free thyroxine with the Amerlex FT4-RIA has become a well-established routine screening method. Compared with the determination of total thyroxine we were able to reduce the number of all supplementary thyroid-specific tests, particularly of TBG, by 30%. Even the frequency of triiodothyronine tests decreased whereas the TSH-levels increased slightly. This is probably an indication of a better diagnosis of incipient hypothyroidism. Especially FT4-values in patients undergoing heparin treatment should be interpreted with special care. By changing from total thyroxine to FT4 we have reduced the department's expenditure by about AS 250 000,- annually, without impairing the accuracy of our diagnostics. Compared with former test combinations, specificity and accuracy have improved.