Validation of a method to replace frozen section during parathyroid exploration by using the rapid parathyroid hormone assay on parathyroid aspirates

Hypothesis: The parathyroid hormone (PTH) content of tissue aspirates is an accurate indicator of parathyroid tissue and can replace frozen section during parathyroid surgery. Design and Setting: Prospective data collection in a tertiary care hospital with a single surgeon. Patients: One hundred sixty-seven consecutive patients completing limited parathyroid explorations. Interventions: Parathyroid adenomas removed during limited parathyroid exploration were aspirated through a 22-gauge needle into 0.5-mL isotonic sodium chloride solution and the solution held on ice in a purple-top tube. Aspirates of in situ thyroid tissue were also taken for comparison. Samples were then assessed for PTH content at the same time the serial blood samples were routinely assessed to monitor the physiologic impact of the surgery. Main Outcome Measure: The PTH content of tissue aspirates was compared with histologic identification of removed putative parathyroid tissue. Results: Elevated tissue PTH content was associated with the identification of the tissue of origin as parathyroid in every case. Tissue aspirates from pathologically proven parathyroid tissue had a mean PTH level of at least 1691 pg/mL, with 160 of the aspirates having values exceeding the upper limit of the assay. This measure was significantly higher than values obtained from thyroid aspirates, which had a mean PTH level of 88 pg/mL (P <.01), reflective of blood levels at the time of aspiration. Using the 99% confidence interval of histologically confirmed parathyroid glands as the lower limit of a positive test result at 16 10 pg/mL, tissue aspirate PTH assay has a sensitivity of 97% and a specificity of 100%., Conclusions: Positive identification of removed tissue as parathyroid is a necessary adjunct to limited parathyroid exploration, where decreases in false-positive blood PTH levels can be a result of operative manipulation of the neck. Analysis of tissue PTH content during the same assay that is being used for assessing blood PTH concentration is an efficient and accurate method for identifying the tissue with certainty. This measure also prevents the occasional ambiguity in frozen sections of parathyroid tissue that apparently contain thyroidlike colloid material.