Relationship between Thyrotropin and Thyroxine Changes during Recovery from Severe Hypothyroxinemia of Critical Illness*

Abstract

In a prospective study of critically ill hypothyroxinemic we assessed the relationship between serum TSH and T4 during the return of serum T4 to normal during recovery. In this longitudinal study of 60 patients with a variety of critical illnesses, including burns, septicemia, and acute renal failure, serum T4 fell to less than 2.7 micrograms/dl (35 nmol/liter) in 24 patients, of whom 14 survived with return of T4 to normal. A rise in total T4 of more than 1.9 microgram/dl (25 nmol/liter) within 96 h occurred 13 times in 10 patients, while 4 patients had slower increases in T4. All 13 episodes of rapid T4 rise [1.7 +/- 0.8 (+/- SD) to 5.6 +/- 2.1 micrograms/dl] were associated with a marked increase in serum TSH (1.1 +/- 0.8 to 7.0 +/- 5.2 mU/liter), and TSH was transiently above normal during 8 episodes of T4 recovery. In the 6 episodes with sampling less than 6 h apart, the TSH rise consistently preceded the T4 rise. In the 4 patients who received dopamine, TSH and T4 remained low until cessation of therapy. During the TSH rise, only minor changes, which could not account for the increase in total T4, occurred in T4-binding globulin (12.9 +/- 3.3 to 14.8 +/- 3.3 mg/liter), prealbumin (208 +/- 73 to 234 +/- 82 mg/liter), and albumin (28.3 +/- 2.9 to 31.9 +/- 2.9 g/liter). Mean free T4 increased (0.60 +/- 0.34 to 1.45 +/- 0.56 ng/dl), as did total T3 (16 +/- 14 to 76 +/- 44 ng/dl), during the phase of TSH rise, suggesting that the increase in TSH was not simply a consequence of diminished negative feedback due to increased plasma binding. The very close and consistent temporal relationship between TSH and T4 during the recovery phase suggests that TSH may have an essential role in the return of T4 to normal during recovery from critical nonthyroidal illness.

The role of cytokines and cortisol in the non-thyroidal illness syndrome following acute myocardial infarction

“…For this reason free T 4 was also estimated by a second method (ELISA) and the changes were similar. Impairment of thyroxine transportation into tissues or reduced serum clearance rate probably due to low cardiac output from the myocardial dysfunction could explain the 'higher T 4 state' in our group I patients (3 elevation of TSH in association with an increase of T 4 has been described in a number of patients with low T 4 recovering from critical illness due to a variety of causes, including AMI (18). It is noteworthy that TSH rose significantly in the group II of our patients with the better prognosis, indicating a more rapid recovery phase compared with group I.…”

The effects of iron deficiency anemia on the thyroid functions

“…20,21 Kokei et al found normal FT4 and higher TSH levels in animals with non-thyroidal diseases. 22 In our study, secondary and subclinical hypothyroidism was determined in a significant portion of our patients (52%).…”

Thyroid hormone alterations in trauma patients requiring massive transfusion: An observational study

“…The rise in TSH during recovery consistently preceded that of free T3 and free T4, suggesting that this rise is necessary in some patients to return thyroid hormone homoeostasis to normal during recovery. [16] These data also suggest that group C recovered earlier than group M, but both groups would have recovered by the second week of hospitalization. Compared with the changes after elective surgery, those in patients with shock or injury have a more rapid onset, greater intensity, and longer duration.…”

“…[16] Vitek et al [14] proposed a biphasic dysfunctional thyroid response in injured patients, with an initial brief rise in TSH and T3 levels followed by a subsequent reduction within 6-18 hours. In that study, the mean interval between injury and hospital admission was 96±38 min, whereas the corresponding intervals in groups M and C of our study were 47.2±21.8 and 51.5±13.9 min, respectively.…”