Spurious intraoperative PTH results observed with 2^nd, but not with 3^rd generation PTH assays

We report here an interference that has been observed with 2^nd generation PTH assays (PTH2), but not with 3^rd generation PTH ones (PTH3), during PTH monitoring occurring in a surgical intervention for the resection of a parathyroid adenoma. The patient was cured and calcium levels returned to normal the next day, but PTH did not decrease with PTH2 whereas it decreased by 50% with PTH3 assays during the intervention. The reason is probably a PTH fragment released by the parathyroid gland during surgery. This fragment possesses the C-terminal part of the peptide but lacks the first amino-acids and may thus be considered as a member of the non-(1-84) PTH fragments family. It has also a longer half-life than 1-84 PTH. To avoid reporting spurious results to the surgeons, we thus recommend using PTH3 assays for monitoring of intra-operative PTH.