[A patient showing increased T3 and T4 levels due to ALP-interfering substances and heterophilic antibody].

A 73-year-old male, who underwent resection of soft palate cancer and was under treatment for esophageal ulcer at our medical department, complained of palpitation. On the suspicion of hyperthyroidism, enzyme immunoassay (EIA) was performed. T3 and T4 were increased, and FT4 and TSH were normal. However, T3 and T4 measured again by radioimmunoassay (RIA) were normal. Therefore, the patient serum was examined for interfering substances such as antibody against bovine intestinal alkaline phosphatase (ALP) and heterophilic antibody. Substances interfering with ALP and anti-rabbit IgG human antibody were detected. It is necessary to consider the possible presence of these substances when results of EIA are evaluated.