Analytical and clinical validation of parathyroid hormone (PTH) measurement in fine-needle aspiration biopsy (FNAB) washings

• Localization of parathyroid prior to surgery is desired in recurrent primary hyperparathyroidism.
• Measurement of PTH in FNAB washings is useful for parathyroid tissue identification.
• Assay- and collection-specific PTH FNAB cut-offs were established.

BackgroundParathyroid hormone (PTH) quantitation in fine needle aspirate biopsy (FNAB) saline washings complements current modalities for parathyroid tissue localization.ObjectivesTo establish the performance characteristics of the Roche Elecsys intact PTH immunoassay in FNAB needle washings and its diagnostic performance for the identification of parathyroid tissue.Design and methodsAccuracy, precision, reportable range, and analytical specificity and sensitivity for the intact PTH immunoassay in FNAB needle washings were established. For clinical validation, 93 specimens from 79 patients were evaluated. Diagnostic cut-offs were established via receiver operator characteristic (ROC) curve analysis. Performance of PTH in FNAB needle washings was compared to cytology.ResultsMeasurement of the PTH in FNAB needle washings demonstrated a matrix interference that was overcome by supplementation of the samples with a protein based matrix prior to analysis. ROC area under the curve (AUC) was 0.96 for PTH in FNAB needle washings. A PTH concentration ≥ 100 pg/mL showed 100% specificity and 82% sensitivity for identifying parathyroid tissue. On histology-confirmed parathyroid specimens, 21/38 (55%) were correctly identified by cytology; whereas 31/38 (82%) were identified by PTH.ConclusionsMeasurement of PTH in FNAB washings complements cytology for identification of parathyroid tissue. Analytical validation to exclude interference in the PTH immunoassay and proper localization of the parathyroid tissue by ultrasound is necessary to ensure the robustness of the method.