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

We report here an interference that has been observed with 2nd generation PTH assays (PTH2), but not with 3rd 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.