Table 2.

Summary of serum 3,5-T2 concentrations in humans observed under physiological (a) and pathophysiological (b) conditions.

a) Physiological conditions:

• Serum 3,5-T2 and 3T1AM concentrations as analyzed by specific mAb-based CLIA do not mirror the dynamics of T3 (or T4) after substitution with T4, T3, or T3-sulfate in healthy individuals or hypothyroid patients • Inter-individual differences in 3,5-T2 and 3T1AM serum concentrations • Remarkably stable individual 3,5-T2 and 3T1AM serum concentrations • Discrepancy between 3,5-T2 serum concentrations determined by CLIA and LC-MS/MS • No clear correlation to TSH, T4, and T3 concentrations • No evidence from these studies supporting the postulated metabolic pathway in humans: T4 → T3 → 3,5-T2 → 3T1AM • Serum 3,5-T2 concentrations are correlated to trigonelline, hippurate, and 3-aminoisobutyrate concentration in urine of healthy individuals (“coffee signature”).

b) Elevated serum concentrations of 3,5-T2 in patients:

• Sepsis • Non-survivors of ICU • Postoperative atrial fibrillation (POAF) • Impaired renal function • Oral T4 supplementation.