The third patient is a 58-year-old female with a single kidney and nephrotic syndrome. She complained of feeling weak, dry skin, alopecia, and severe fatigue, clinically consistent with hypothyroidism. Her 24-hour urinary protein was approximately 1 g/day. Her low serum thyroxine-binding globulin (TBG, 5.6 microg/mL, reference range 13 - 39 microg/mL), the main thyroid hormone binding protein, suggests that she is losing TBG and thyroid hormones in her urine. Free and total thyroid hormones were all low as measured by mass spectrometry (Table 1), indicating that she was biochemically hypothyroid, despite her normal TSH concentration at 1.33 microIU/mL. She will shortly begin thyroid hormone therapy.
Our studies on the effect of ACTH administration on serum TSH concentration were conducted in the morning between 8AM and 9AM. Sixty minutes post ACTH simulation, TSH showed a mean decrease of 17% compared to baseline with minimum and maximum decreases of 6.9% and 42.9% (Figure 1). This effect is presumably caused by the increased steroid concentrations as a result of the ACTH stimulation. This further supports our contention that TSH measurement is interfered with by many compounds which could affect the diagnosis of hypothyroidism.