Thyroid hormone binding inhibition in critically ill patients--who is the inhibitor?

In 31 severely ill patients of our intensive care unit an increased thyroid hormone binding inhibition detected by quantitative measurement of the effect of ether extracts of patients' sera on thyroxine tracer binding to TBG was found. As free fatty acids in serum were diminished in these patients, their postulated role as binding inhibitors in the "low T4 syndrome" of critically ill patients must be questioned. It cannot be excluded that THBI assays demonstrating this inhibition measure artefacts caused by heparine-induced in vitro lipolysis.