Serum Angiotensin-Converting Enzyme in Severe Nonthyroidal Illnesses Associated with Low Serum Thyroxine Concentration

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Abstract
We evaluated serum angiotensin-converting enzyme levels as an index of thyroid hormone action in severe systemic illness. Angiotensin-converting enzyme was elevated in hyperthyroid patients (37.3 ± 3.2 U/mL, p < 0.01) and depressed in hypothyroid patients (17.9 ± 1.4 U/mL, p < 0.05). Compared with normal controls (22.6 ± 1.6 U/mL), patients in an intensive care unit with free thyroxine index greater than 5.0 had normal angiotensin-converting enzyme levels (19.1 ± 2.5 U/mL), but patients with a free thyroxine index less than 5.0 had angiotensin-converting enzyme levels significantly lower than the normal and hypothyroid groups ( 10.7 ± 1.0 U/mL, p < 0.05). A group of patients in an intensive care unit with alcoholic liver disease (known to elevate angiotensin-converting enzyme) and a low free thyroxine index had depressed angiotensin-converting enzyme levels (16.9 ∓ 1.5 U/mL, p < 0.01). A strong correlation was seen in the combined groups of all patients studied between levels of angiotensin-converting enzyme and a free thyroxine index (r = 0.70, p < 0.01) and free T3 index (r = 0.72, p < 0.01).