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CASE REPORT article
Front. Endocrinol.
Sec. Bone Research
Volume 16 - 2025 | doi: 10.3389/fendo.2025.1564352
This article is part of the Research Topic Phosphate handling: from cells to human View all 7 articles
Case Report: Falsely elevated PTH level in a young woman caused by immunoassay interference resulting from macro-PTH
Provisionally accepted
Giuseppe Perruolo 
Lidia Santarpia 
Cristina Morelli 
Domenico Rendina 
Federica Mormone 
Giusy Ferraro 
Pietro Formisano *
Francesco Oriente *- University of Naples Federico II, Naples, Italy
Elevated parathyroid hormone (PTH) levels usually suggest an underlying parathyroid disorder. However, immunoassay interference, such as macro-PTH, can result in falsely elevated readings, leading to diagnostic inaccuracy. Here, we report the case of a 27-year-old woman with persistently elevated PTH levels despite normal serum calcium, phosphate, and vitamin D.Aside from a history of nephrolithiasis, the patient was asymptomatic and exhibited no parathyroid abnormalities detected on ultrasound, sestamibi scintigraphy, or choline positron emission tomography-computed tomography (PET-CT) scans. To investigate potential immunoassay interference, a polyethylene glycol (PEG) 6000 precipitation assay was performed, which showed a decrease of PTH levels from >1200 pg/mL to approximately 40 pg/mL, corresponding to a 97% reduction. To validate the specificity of this technique, the same procedure was conducted on sera from two patients with elevated PTH levels due to known parathyroid pathologies. PTH levels decreased from 771 to 271 pg/ml and 527 to 146 pg/ml, corresponding to 65 and 72% reduction, respectively. The following results indicated that the PEG precipitation primarily affected the macro-PTH in our patient's sample while leaving intact PTH relatively unaffected in the control group. This report suggests that unexpectedly high PTH levels in the presence of otherwise normal laboratory values and imaging results could indicate the possibility of immunoassay interference.PEG 6000 precipitation is a valuable diagnostic tool for macro-PTH detection, although further refinement of immunoassay techniques may be needed to enhance the reliability of PTH measurements in clinical practice.
Keywords: Parathyroid Hormone, Macro-PTH, Chemiluminescent immunoassay, Analytical interference, polyethylene glycol
Received: 21 Jan 2025; Accepted: 24 Mar 2025.
Copyright: © 2025 Perruolo, Santarpia, Morelli, Rendina, Mormone, Ferraro, Formisano and Oriente. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Pietro Formisano, University of Naples Federico II, Naples, Italy
Francesco Oriente, University of Naples Federico II, Naples, Italy
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