Influence of thyrotropin and thyroid volume on basal serum calcitonin

Thyroid volume was found to be a determinant of serum calcitonin levels in animal models and in thyroid-healthy subjects, as recently reported. This study aims to evaluate if this finding is confirmed in patients undergoing ultrasonography-guided fine-needle aspiration cytology of suspicious thyroid nodules. A dataset of 561 patients including basal serum FT4, FT3, TSH, calcitonin, thyroid volume, anti-thyroperoxidase antibodies (TPOAb), and cytology report, was retrospectively analysed. The median thyroid volume was 20.5 ml (14.5-26.8) in males and 12.0 ml (9.3-17.0) in females (p<0.001). The overall median serum calcitonin value was 2.00 pg/ml (2.00-3.10). A Spearman's correlation was performed between serum calcitonin levels and thyroid volume, showing a weak direct relationship (rs=0.173, p<0.001). This relationship is confirmed both in the smokers group (rs=0.337, p=0.003) and in non-smokers group (rs=0.115, p=0.012), and both in the TPOAb-positive patients (rs=0.419, p<0.001) and negative ones (rs=0.107, p=0.025). There is no correlation between serum TSH and calcitonin levels. In patients grouped according to morphologic diagnosis, calcitonin levels are slightly higher in the high-volume groups: the interquartile range was 2.00-2.00 pg/ml in the atrophy, 2.00-2.82 pg/ml in the normal volume, and 2.00-3.85 pg/ml in the goiter group (p=0.02). When males and females are computed separately, the statistical significance is lost. In conclusion, thyroid volume can mildly influence calcitonin levels. Gender acts as a "surrogate marker" of thyroid volume and the application of a gender-specific cut-off can probably overcome this issue in clinical practice.