Prospective evaluation of the rate and impact of hemolysis on intraoperative parathyroid hormone (IOPTH) assay results.
Intraoperative parathyroid hormone (IOPTH) is commonly used during minimally invasive parathyroidectomy. Retrospective evidence suggested that hemolysis may artificially lower IOPTH results. Falsely decreased IOPTH measurements could result in either failed parathyroidectomy or unnecessary bilateral neck exploration. A total of 130 IOPTH specimens from 30 patients were assayed before and after induction of mechanical hemolysis using a vortex and inert sterile glass beads. Free hemoglobin (Hg) was measured as a surrogate for extent of hemolysis. Paired sample t test was used for comparison of matched prehemolysis and posthemolysis specimens. Of the samples, 16.9% were hemolyzed at the baseline (11 of 72 pre-excision, 11 of 55 postexcision). We successfully induced moderate hemolysis (ΔHg 0.1-1.0 mg/DL) in 66 samples that had minimal hemolysis at baseline. In these, mechanical hemolysis increased free Hg by an average of 0.37 mg/DL (533%; mean posthemolysis free Hg = 0.43; moderate hemolysis) and lowered PTH values by an average of 39% (median = 36%, SD = 11%; P = .002). The decrease in PTH was related to the extent of hemolysis induced (r = 0.51; P < .001), but was unrelated to the specimen's baseline (true) PTH (P = .24). In 12 of 30 patients, the experimentally hemolyzed pre-excision PTH value would have reduced the 50% threshold sufficiently to cause a false-negative result. In 6 of the 30 parathyroidectomies, a hemolyzed postexcision PTH value would have decreased PTH value sufficiently to cause a false-positive result. Hemolysis of IOPTH specimens occurs commonly and falsely reduces PTH results. In 18 of 30 patients, this effect was sufficient to have contributed to either a false-positive or false-negative IOPTH result.