Important Note

Human Anti-Mouse Antibodies (HAMA) may be present in samples from patients who have received immunotherapy utilizing monoclonal antibodies. Additionally, other heterophile antibodies such as human anti-goat antibodies may be present in patient samples. Manufacturers formulate assays to minimize the effects of these antibodies; however careful evaluation of patient results must be done when patients are known to have such antibodies.

Non-thyrometabolic disorders may cause abnormal Free T3 levels. Anticonvulsant drug therapy (particularly phenytoin) may result in decreased Free T3 levels due to an increased hepatic metabolism, and secondary to displacement of hormone from binding sites. Anti-inflammatory drugs such as salicylate and phenylbutazone also compete for hormone binding sites, but their effect on Free T3 levels has not been clearly defined. Patients on Heparin therapy may have elevated Free T3 levels due to release of non-esterified fatty acids, which can alter the relationship between free and bound hormones. Determination of thyroid status in-patients with non-thyroidal illness (NTI) should be interpreted with caution.

Access Free T3: potential of falsely elevated results when biotin concentrations are > 10 ng/mL.