Aim: The biological diagnostic of Hashimoto thyroiditis (HT) is based on higher than normal levels of antithyroperoxydase antibodies (ATPO). Our goal was to establish the cut-off limit of normality (the upper limit) for ATPO in our thyroid normal patients. This limit and not that of the laboratory, should be used as diagnosis of Hashimoto thyroiditis.
Material and method: 1. ATPO was investigated in patients with normal level of thyroid hormones (euthyroidism) and normal ultrasound of thyroid (linear probe at 7.5 MHz). 2. ATPO was analyzed in several Bucharest laboratories, accredited for this investigation. The laboratory cut-off limit for normality was 34 Ul/ml. 3. Conventionally, the normality is considered as the average (mean) plus/minus standard deviation multiply by 2.
Results: A. Patients: 268; women, 227, men, 41, age, average, 45, 87, median, 44; average TSH, 1.8 mUI/ml, FT4, 15.6 nmol/l.
B. ATPO level was: average: 8.65 UI/ml, standard deviation: 7.22. Therefore, the upper limit should be 23.08 UI/ml.
Discussion: Based on 34 UI/ml cut-off limit, we registered 1510 patients with HT (higher ATPO), 129 patients with only high antithyroglobuline thyroiditis (ATG-T)(lower ATPO), and 108 patients with idiopathic myxedema (hypothyroidism, lower ATPO/ATG, and inflammatory ultrasound signs). Considering ATPO cut-off 23 UI/ml, 15 (11.9%) ATG-T and 6 (4.6%) myxedema were in fact HT patients.
Conclusions: 1. Using the date from our patients, the cut-off limit for ATPO should be 23 UI/ml and not 34 UI/ml. 2. Based on 23 UI/ml cut-off limit, the number of patients with Hashimoto thyroiditis increased by 9l.5%.