Endocrine Abstracts

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 7.5–10 MHz). 2. ATPO was analyzed in several Bucharest laboratories, accredited for this investigation. The laboratory cut-off limit for normality was 34 ui/ml. 3. Conventionally, the normality is considered as the average (mean) plus/minus standard deviation multiply by 2.

Results: A. Patients: 404; women - 328 (77%), men – 76 (23%); age: average - 44.6, median - 42; average TSH: 1.84 mui/ml, FT4, 15 nmol/l. B. ATPO level was: average: 8.65 ui/ml, standard deviation: 6.88. Therefore, the upper limit should be 21.89 ui/ml.

Discussion: Based on 34 ui/ml cut-off limit, we registered 1750 patients with HT (higher ATPO), 205 patients with only high antithyroglobuline thyroiditis (ATG-T) (low ATPO), 126 patients with idiopathic myxedema (hypothyroidism, lower ATPO/ATG, and inflammatory ultrasound signs) and 1875 patients control, with other thyroid diseases (mostly thyroid nodules). Considering ATPO cut-off as 21.89 ui/ml, 29 patients with ATG-T (14.15%) and 12 patients with idiopathic myxedema (9.52%) should be considered, in fact, HT patients. Moreover, 135 control patients (7.19%) with ultrasound inflammatory signs should be considered HT patients, too.

Conclusions: 1. Using the data from our patients, the cut-off limit for ATPO should be 21.89 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 10.3%. 3. Every research group should establish its specific cut off for ATPO level.