Abnormalities in thyroid hormone metabolism are common in critically ill patients. However, it is not known if these patients are truly hypothyroid at tissue level. Erythrocyte zinc has been shown to be a tissue marker of thyroid hormone status. In this study we have measured the erythrocyte zinc in critically ill patients.
In this observational study we measured the zinc content of young erythrocytes in blood samples from 33 healthy subjects, 26 hypothyroid patients, four hyperthyroid patients, and 44 patients in the intensive care unit – 22 of these were admitted after a major surgical procedure (surgical group) and the other 22 patients had a variety of conditions (non-surgical group). Erythrocytes were separated according to age by centrifugation. Plasma thyroid hormone concentrations were abnormal in 70% of the critically ill group. Erythrocyte zinc was significantly lower in hyperthyroid patients and higher in hypothyroid patients. In the non-surgical patients, erythrocyte zinc of young cells (median 256 μmol/L of cells) was significantly higher than (p<0.01) the corresponding cells in the healthy controls (202 μmol/L of cells), whereas in the surgical group it was not different (197 μmol/L of cells). We conclude that in non-surgical critically ill patients, erythrocyte zinc content is higher, suggesting that these patients may be hypothyroid at tissue level.