[Accuracy in thyroid hormonology: evaluation of free T4 by five immunometric methods using cold markers]

During a comparative multicentric evaluation, five commercially available non-isotopic methods for FT4 measurement were tested. As with the radioactive methods the problem with accuracy is again evident. This is true both for setting reference values and standards as well as for the specificity of the methods. The authors demonstrated highly significant correlations as described in recent papers: many of the values may, however, be up to double value in one center compared to another despite the correlation of 0.90.