Unlocking the diagnostic potential of parathormone washout: a path to accurate parathyroid tumor localization

Accurate tumor localization is necessary for the application of minimally invasive surgery, which is preferred in the treatment of primary hyperparathyroidism. Parathormone-washout (PTH-WO) is parathyroid fine-needle aspiration followed by PTH measurement in the needle washout fluid. This study aimed to determine appropriate cutoff values for the PTH-WO method.

A total of 402 PTH-WO assays from 339 patients were included in the study. The diagnostic accuracy of the test was assessed by accepting as a positive result a PTH-WO result higher than the serum PTH level [PTH-WO/serum PTH(PTH ratio)>1]. In addition, a cutoff value for the test was established by evaluating the PTH washout results obtained in comparison with postoperative histopathology. Undiluted test results were not included to obtain a clear numerical value in this evaluation. The results of parathyroid scintigraphy and fine needle aspiration biopsy (FNAB) were compared with postoperative histopathology.

While 309 (76.86%) of the PTH-WO procedures were considered positive, 93 (23.13%) were considered negative if the PTH ratio was > 1. When these results were compared with the postoperative histopathology, the test's sensitivity was 92.51%, and the specificity was 100.00%. In the analysis of the remaining 292 PTH-WO samples after excluding the undiluted ones, the sensitivity and specificity of the method were 92.3% and 94.1%, respectively, with a PTH ratio > 0.99. With a cutoff value of 99.5 ng/l for PTH-WO value, 93.1% sensitivity and 94.3% specificity were obtained. The sensitivities of parathyroid scintigraphy and FNAB were 53.4% and 15.3%, respectively.

The PTH-WO method is safe and cheap, with high sensitivity and specificity in localizing parathyroid tumor. In cases where radiological methods cannot achieve localization with specified cutoff values, it has high diagnostic accuracy.