[Modification of the FT4-level and the nonspecific peripheral thyroid parameter by heparin]

Heparin produces changes in FT4-levels both in vivo and in vitro as determined by commercial kits. Methods utilising the principle of equilibrium dialysis show significant increases whereas methods using T4-tracer analogue techniques reveal marked decreases in FT4-values. Possible clinical side-effects of heparin administration such as heparin-induced hyperthyroidism and tachyarrhythmias are discussed. The present results confirm the FT4-decreasing effect of in vivo and in vitro administration of heparin with FT4-RIAs based on the tracer analogue technique; however, the unspecific peripheral thyroid parameter of systolic time-intervals did not reveal any tendency towards hyperthyroidism. Also the discrepant results dependent on the method used, indicate that, following heparin administration FT4-levels do not reflect that hormone concentration is relevant to the metabolism of the whole body.