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Purpose <p>The reliability of parathyroid hormone (PTH) assays in fine-needle aspirate (FNA) samples remains less established than in serum, particularly regarding assay variability and differences by nodule composition. This study evaluated inter-assay variability of measuring parathyroid hormone in fine-needle aspirates (PTH-FNA) washout samples across solid and cystic nodules.</p> Methods <p>Patients with indeterminate neck nodules who underwent PTH-FNA testing were retrospectively analyzed. Nodules were classified as solid or cystic, and two commercial radioimmunoassay (RIA) kits (RIAKEY and Immunotech) were compared. Results were defined as positive or negative using each assay’s serum PTH threshold (RIAKEY: 57 pg/mL; Immunotech: 85.8 pg/mL). Spearman’s correlation (<i>ρ</i>) and diagnostic performance were assessed.</p> Results <p>Fifty-eight cases were reviewed; 24 solid nodules (12 parathyroid adenomas [PAs], 12 non-parathyroid nodules [nPNs]), and 11 parathyroid cysts (PCs) were eligible. Among solid nodules, assays showed a strong correlation (<i>ρ</i> = 0.829), with Immunotech yielding slightly higher values; No inter-assay differences were observed in PAs, but nPNs differed significantly (<i>p</i> = 0.006). One PA was false-negative with RIAKEY, while Immunotech produced two false-positive nPNs; overall diagnostic performance was comparable (area under the curve = 0.986 vs. 0.979). For PCs, values were more variable than in solid nodules, albeit the correlation remained strong (<i>ρ</i> = 0.936). RIAKEY yielded significantly higher PTH-FNA values (<i>p</i> = 0.026), with discordant results in two cases.</p> Conclusion <p>PTH-FNA results from two RIA kits were strongly correlated across nodule types. However, assay discrepancies in non-parathyroid and cystic nodules highlight the need for cautious interpretation.</p>

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Inter-Assay Difference of Parathyroid Hormone Radioimmunoassay in Fine-Needle Aspirate from Neck Nodules According to Nodular Component

  • 期刊论文

  • 发表日期：

    2026年4月14日

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  • Soyoon Yoon,
  • Jin-Sook Ryu,
  • Yong-Il Kim,
  • Hee Beom Jeong,
  • Sun Ho Lee,
  • Sae Rom Chung,
  • Chong Hyun Suh,
  • Dong Eun Song,
  • Dong Yun Lee

摘要

Purpose

The reliability of parathyroid hormone (PTH) assays in fine-needle aspirate (FNA) samples remains less established than in serum, particularly regarding assay variability and differences by nodule composition. This study evaluated inter-assay variability of measuring parathyroid hormone in fine-needle aspirates (PTH-FNA) washout samples across solid and cystic nodules.

Methods

Patients with indeterminate neck nodules who underwent PTH-FNA testing were retrospectively analyzed. Nodules were classified as solid or cystic, and two commercial radioimmunoassay (RIA) kits (RIAKEY and Immunotech) were compared. Results were defined as positive or negative using each assay’s serum PTH threshold (RIAKEY: 57 pg/mL; Immunotech: 85.8 pg/mL). Spearman’s correlation (ρ) and diagnostic performance were assessed.

Results

Fifty-eight cases were reviewed; 24 solid nodules (12 parathyroid adenomas [PAs], 12 non-parathyroid nodules [nPNs]), and 11 parathyroid cysts (PCs) were eligible. Among solid nodules, assays showed a strong correlation (ρ = 0.829), with Immunotech yielding slightly higher values; No inter-assay differences were observed in PAs, but nPNs differed significantly (p = 0.006). One PA was false-negative with RIAKEY, while Immunotech produced two false-positive nPNs; overall diagnostic performance was comparable (area under the curve = 0.986 vs. 0.979). For PCs, values were more variable than in solid nodules, albeit the correlation remained strong (ρ = 0.936). RIAKEY yielded significantly higher PTH-FNA values (p = 0.026), with discordant results in two cases.

Conclusion

PTH-FNA results from two RIA kits were strongly correlated across nodule types. However, assay discrepancies in non-parathyroid and cystic nodules highlight the need for cautious interpretation.