Elevated serum diiodotyrosine (DIT) in severe infections and sepsis: DIT, a possible new marker of leukocyte activity.

Ether link cleavage (ELC) of T4 yielding diiodotyrosine (DIT) has recently been shown in vitro to be the major pathway of T4 metabolism in phagocytosing leukocytes. To evaluate this pathway in vivo and the possible clinical relevance of DIT measurements in diseases with increased leukocyte activity, radioimmunological studies on serum levels of DIT and other thyroid parameters were performed in 125 critically ill patients classified into 3 groups with bacterial infections according to the severity of infection and 1 group without infections. While the pattern of iodothyronine and TSH levels typical for severe nonthyroidal disorders, i.e. decreased total T3 and elevated rT3, normal or decreased total T4 and TSH, and normal free T4, was found in all four groups of intensive care patients studied, elevated serum DIT was observed only in those patients whose clinical course was complicated by severe bacterial infections. Serial measurements revealed a close temporal connection between the infection phase and increased DIT levels. Median values and 16th to 84th percentile ranges (in parentheses) of serum DIT (normal range, 0.02-0.55 nmol/L) were as follows: sepsis, 1.38 (0.32-5.14); severe nonsystemic infections such as peritonitis and abscesses, 3.84 (0.24-17.2); moderate infections such as pneumonia and tracheobronchitis, 0.44 (0.18-1.16); and critical illness without infections, 0.14 (0.08-0.30) nmol/L. These elevations of circulating DIT could neither be correlated with changes in renal function nor attributed to drug effects. The results of the present study do not allow any definitive conclusions to be made about the mechanisms underlying the phenomenon of increased serum DIT levels in infections. Apart from this open question, DIT appears to be a relatively specific serum parameter for the presence and course of severe bacterial inflammations. Its measurement could provide useful clinical information, particularly for monitoring the time course of deep-seated infections.