Year: 2026
Type: conference-abstract
Abstract: Introduction Parathyroid hormone (PTH) is a key regulator of calcium and phosphate homeostasis and an essential marker in the evaluation of hyperparathyroidism and chronic kidney disease. In routine practice, PTH is measured using immunometric assays together with serum calcium, phosphate, and vitamin D concentrations. However, circulating PTH includes not only the biologically active intact hormone but also inactive immunoreactive forms, which may lead to falsely elevated results. Despite improved analytical specificity of modern assays, immunoassay interference remains an underrecognized diagnostic problem. Macro-parathyroid hormone (macro-PTH) is a rare high-molecular-weight complex formed by PTH bound to immunoglobulins. It is biologically inactive and not associated with clinical or biochemical features of primary hyperparathyroidism, yet it may closely mimic this condition in routine laboratory testing. Failure to recognize macro-PTH may therefore result in misdiagnosis and unnecessary additional diagnostic procedures. Polyethylene glycol (PEG) precipitation is a simple laboratory technique that enables identification of macro-hormone complexes by selectively removing high-molecular-weight proteins from serum samples. Despite its low cost and diagnostic value, it is not routinely used in the evaluation of discordant PTH results. Case Presentation A 47-year-old woman was referred for evaluation of long-standing suspected primary hyperparathyroidism. For over ten years, persistently elevated PTH concentrations were documented, while total serum calcium remained within the normal range. PTH values ranged from 85 to 563 pg/mL, whereas serum calcium ranged between 8.8 and 9.6 mg/dL. Renal function was preserved, phosphate levels were normal or mildly reduced, and vitamin D deficiency was corrected. PTH was measured using a second-generation chemiluminescent immunoassay (DiaSorin) on the LIAISON XL analyser. The patient had no nephrolithiasis, fragility fractures, or symptoms of hypercalcaemia. Her medical history included autoimmune hypothyroidism treated with levothyroxine. Neck ultrasonography intermittently showed small hypoechoic lesions near the lower pole of the left thyroid lobe, while repeated 99mTc-MIBI scintigraphy with SPECT-CT revealed no pathological uptake. Fine-needle aspiration with PTH measurement in needle washout was negative. Given the marked biochemical–clinical discrepancy, PEG precipitation was performed, resulting in a marked reduction in PTH concentrations (recovery 8%-10%), confirming macro-PTH and excluding primary hyperparathyroidism. Conclusions Macro-PTH is an important diagnostic pitfall. PEG precipitation should be considered in cases of persistent PTH elevation inconsistent with clinical and biochemical findings to avoid misdiagnosis and unnecessary interventions
Institutions: University Clinical Centre, Gdańsk Medical University
Language: English
Subfield: Medical Laboratory Technology
Field: Health Professions
Domain: Health Sciences
Open Access status: hybrid
Estimated APC paid: $4,292
OpenAlex ID: W7213305617