Thyroid Research Thyroid Research Archive Hyperthyroidism

Serum thyroid hormone values and counts of blood eosinophils and monocytes distinguish between Graves' disease and thyroiditis

(November 2002)

The background of the study. Silent (painless) thyroiditis and Graves' disease are common causes of thyrotoxicosis, and distinguishing between them is important because treatment differs. In this study the efficacy of measurements of the ratio of free triiodothyronine (T3) to free thyroxine (T4) in serum and the ratio of eosinophil cells to monocyte cells in blood to differentiate between the two disorders was evaluated.

How the study was done. The study subjects were 111 patients with thyrotoxicosis, of whom 69 had Graves' disease, 21 had silent thyroiditis, and 21 had subacute (painful) thyroiditis. All the patients had high serum free T3 and free T4 concentrations. The diagnoses were based on standard criteria, including measurements of thyrotropin receptor antibodies and thyroid radioiodine uptake.

The results of the study. The mean serum free T3 and free T4 concentrations were higher in the patients with Graves' disease, as compared with the values in the patients with painless thyroiditis or subacute thyroiditis. The mean ratio of serum free T3 to free T4 was higher in the patients with Graves' disease (0.40±0.09) than in the patients with either painless thyroiditis (0.30±0.07, P<0.01) or subacute thyroiditis (0.34±0.06, P<0.01). Among the 28 patients with thyrotoxicosis who had a ratio of serum free T3 to free T4 of <0.3, 79 percent had silent or subacute thyroiditis.

In the patients with Graves' disease, 3.5 percent of white blood cells were eosinophils, as compared with 1.4 percent in the patients with silent thyroiditis (P<0.01) and 1.1 percent in the patients with subacute thyroiditis (P<0.01). The mean ratio of eosinophils to monocytes was 0.8 in the patients with Graves' disease, 0.3 in the patients with silent thyroiditis, and 0.2 in the patients with subacute thyroiditis (P<0.01).

The conclusions of the study. Measurements of the ratio of free T3 to free T4 in serum and the ratio of eosinophils to monocytes in blood help to distinguish between Graves' disease and silent thyroiditis or subacute thyroiditis as causes of thyrotoxicosis.

The original article. Izumi Y, Hidaka Y, Tada H, Takano T, Kashiwai T, Tatsumi K, Ichihara K, Amino N. Simple and practical parameters for differentiation between destruction-induced thyrotoxicosis and Graves' thyrotoxicosis. Clin Endocrinol 2002;57:51-8.