Thyroid Hormone Metabolism in Hypermetabolic Patients with Haematological Disorders

Summary Turnover tracer studies of T 4 and T 3 using the single injection, noncompartmental approach were performed in 6 hypermetabolic patients with haematological disorders (HHD) (basal metabolic rate (BMR): median 141%, range 122-166%), in 10 controls with stable, nonthyroidal illness (NTIC), and in 14 healthy controls (HC). The main finding was an increase of approximately 30% of the production rate (PR) of both T 4 and T 3 in patients with HHD. Median PR of T 4 was 134 nmol/day × 70kg in HHD, compared to 78 nmol/day × 70 kg in NTIC (P < 0.05) and 98 nmol/day × 70 kg in HC (p < 0.1), whereas median PR of T 3 was 40.3 nmol/day × 70 kg in HHD, compared to 25.6 nmol/day × 70 kg in NTIC (P < 0.01) and 31.1 nmol/day × 70kg in HC(P < 0.1). An increase of similar magnitude was found for the apparent distribution volume and the pool size of both T 4 and T 3 . In contrast, the mean transit times of the hormones were similar in the 3 groups. Patients with HHD had normal levels of basal serum TSH as well as of the TSH response to TRH. Only PR of T 3 correlated to the BMR (R = 1.00, P < 0.02). The data are compatible with an increased consumption of thyroid hormones by malignant haematologic cells, and the increase of BMR seems to be dependent on the production of T 3 .