Is soluble CD25 antigen (interleukin-2 receptor) a useful parameter for differential diagnosis of thyrotoxicosis?

Soluble CD25 antigen was measured in 28 patients with Graves' disease and 20 patients with thyroid autonomy in order to address the question of whether this parameter could be used in the differential diagnosis of thyrotoxicosis. Soluble CD25 was significantly elevated in active Graves' disease (2430 +/- 442 U/ml, mean +/- SEM) compared to patients with thyroid autonomy (1295 +/- 225 U/ml, mean +/- SEM). However, compared to normal controls (mean 605 +/- 49 U/ml), both groups of patients had significantly elevated CD25 plasma levels. Investigations in thyroidectomized thyroid cancer patients on and off T4 suppressive therapy showed no influence of T4 on the CD25 level. Soluble CD25 concentrations did not differ in thyroid cancer patients compared to normal controls. We conclude that soluble CD25 may indicate a stimulation of the immune system with high sensitivity; however, due to the low specificity of elevated CD25 levels, its usefulness for differential diagnosis of thyrotoxicosis is limited.