['Some extra-thyroid actions of thyroid stimulating hormone (TSH), such as an in vitro action on bone, have been described. Our aim was to evaluate in vivo the acute effect of a recombinant human TSH (rhTSH)-induced TSH surge on Osteoprotegerin (OPG) and receptor activator of the nuclear factor-kappaBeta (RANK-L) levels in patients under levo-thyroxine (L-T4) therapy.', '24 patients with differentiated thyroid carcinoma (DTC) were studied. Standard rhTSH testing was performed. OPG, RANK-L, TSH, thyroid hormones, thyroglobulin and several parameters of bone metabolism were evaluated.', 'Baseline OPG and RANK-L levels were in the range of our reference population. An inverse correlation between OPG and spinal Z-score (p=0.029) and between RANK-L and age (p=0.018) or urinary calcium/creatinine ratio (p=0.011) was detected. After rhTSH administration, a significant (p<0.001) increase in TSH was found. No significant increase in OPG or RANK-L levels after rhTSH was observed. No correlation was detected between TSH peak value after rhTSH and maximal percentage change in OPG or RANK-L. A slight increase in urinary cross-links after rhTSH was found.'] Does recombinant human thyroid stimulating hormone acutely change serum osteoprotegerin and soluble receptor activator of nuclear factor-kappaBeta ligand in patients under evaluation for differentiated thyroid carcinoma?