Antithyroid Drug-Induced Agranulocytosis: Special Reference to Normal White Blood Cell Count Agranulocytosis

This retrospective study was aimed at revealing the incidence of normal white blood cell (WBC) count agranulocytosis in patients treated with antithyroid drugs (ATDs). From January 1975 to December 2001, 109 patients (0.35%) presented with ATD-induced agranulocytosis at our clinic. In 18 patients (16.5%), the WBC count exceeded 3.0 × 10⁹/L at the onset of agranulocytosis. Ten showed a downward trend in WBC count (3.0-3.9 × 10⁹/L) after the initiation of ATDs. Four had symptoms of infection. In the remaining 4 patients, routine WBC and granulocyte count monitoring detected an agranulocytosis. During the first 3 months of ATD treatment, 3347 patients (10.9%) had WBC count 3.0-3.9 × 10⁹/L even once with no symptom and normal granulocyte count and 26,672 patients had WBC count ≥ 4.0 × 10⁹/L with no symptom and normal granulocyte count. When agranulocytosis was found, twelve patients with normal WBC count agranulocytosis (0.36%) had WBC count 3.0-3.9 × 10⁹/L with no symptom, whereas only 2 patients with agranulocytosis (0.008%) had WBC count ≥ 4.0 × 10⁹/L with no symptom. In conclusion, clinicians should take normal WBC count agranulocytosis into consideration at least during the first 3 months of antithyroid drug therapy, especially when WBC count is 3.0-3.9 × 10⁹/L.