CONTEXT AND OBJECTIVE: The primary purpose of this study was to detect and 
quantify 3-iodothyronamine (T(1)AM), an endogenous biogenic amine related to 
thyroid hormone, in human blood.
DESIGN: T(1)AM, total T(3), and total T(4) were assayed in serum by a novel HPLC 
tandem mass spectrometry assay, which has already been validated in animal 
investigations, and the results were related to standard clinical and laboratory 
variables.
SETTING AND PATIENTS: The series included one healthy volunteer, 24 patients 
admitted to a cardiological ward, and 17 ambulatory patients suspected of 
thyroid disease, who underwent blood sampling at admission for routine 
diagnostic purposes. Seven patients were affected by type 2 diabetes, and six 
patients showed echocardiographic evidence of impaired left ventricular 
function.
INTERVENTIONS: No intervention or any patient selection was performed.
MAIN OUTCOME MEASURES: serum T(1)AM, total and free T(3) and T(4), routine 
chemistry, routine hematology, and echocardiographic parameters were measured.
RESULTS: T(1)AM was detected in all samples, and its concentration averaged 
0.219 ± 0.012 pmol/ml. The T(1)AM concentration was significantly correlated to 
total T(4) (r = 0.654, P < 0.001), total T(3) (r = 0.705, P < 0.001), glycated 
hemoglobin (r = 0.508, P = 0.013), brain natriuretic peptide (r = 0.543, P = 
0.016), and γ-glutamyl transpeptidase (r = 0.675, P < 0.001). In diabetic vs. 
nondiabetic patients T(1)AM concentration was significantly increased (0.232 ± 
0.014 vs. 0.203 ± 0.006 pmol/ml, P = 0.044), whereas no significant difference 
was observed in patients with cardiac dysfunction.
CONCLUSIONS: T(1)AM is an endogenous messenger that can be assayed in human 
blood. Our results are consistent with the hypothesis that circulating T(1)AM is 
produced from thyroid hormones and encourage further investigations on the 
potential role of T(1)AM in insulin resistance and heart failure.