LC-MS/MS Measurement of Parathyroid Hormone-Related Peptide

Area of Science:

• Biochemistry
• Analytical Chemistry
• Oncology

Background:

• Parathyroid hormone-related peptide (PTHrP) plays a role in bone metastasis formation.
• PTHrP measurement is crucial for diagnosing and managing hypercalcemia of malignancy.

Purpose of the Study:

• To develop and validate a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying PTHrP.
• To establish sex-specific reference intervals for PTHrP.
• To assess the clinical performance of the developed assay.

Main Methods:

• Plasma samples were subjected to antibody-based enrichment of PTHrP.
• Enriched PTHrP was digested with trypsin.
• Tryptic peptides were analyzed using 2D LC-MS/MS in multiple reaction monitoring mode.

Main Results:

• The LC-MS/MS method demonstrated a lower limit of quantification of 0.6 pmol/L and high precision (<10% total imprecision).
• The assay showed poor agreement with traditional radioimmunoassay (RIA) methods, with LC-MS/MS detecting significantly higher PTHrP positivity rates (26.6% vs 1.9%).
• Clinical evaluation yielded an area under the ROC curve of 0.874 for hypercalcemia detection.

Conclusions:

• Commercial RIAs substantially underestimate circulating PTHrP levels, leading to potential false-negative results in hypercalcemia diagnosis.
• The developed LC-MS/MS method provides a more accurate assessment of PTHrP.
• Elevated PTHrP in postmenopausal women with low BMI may correlate with increased osteoporosis incidence.