Reference interval of parathyroid hormone based on the Korea National Health and Nutrition Examination Survey 2024.

BACKGROUND: Parathyroid hormone (PTH) plays a pivotal role in calcium–phosphate metabolism and bone health; however, interpretation of PTH concentrations remains challenging because of biological variability and substantial analytical heterogeneity among assays. In Korea, population-based data on PTH reference intervals are limited, and assay-specific reference intervals have not been well established. METHODS: We evaluated the reference interval of serum PTH using data from the Korea National Health and Nutrition Examination Survey (KNHANES) 2024. A stepwise, biologically informed selection process was applied to define reference populations by progressively excluding participants with conditions known to influence PTH metabolism, including impaired renal function, vitamin D insufficiency, and abnormalities in mineral-related biochemical parameters (calcium, magnesium, phosphate, and alkaline phosphatase). RESULTS: Among the 6,997 participants in the KNHANES 2024 dataset, serum PTH measurements were available for 4,502 adults aged ≥ 40 years. The high prevalence of supplement use and age-restricted sampling limited the size of suitable reference populations. The number of survey-design–valid participants frequently fell below the recommended threshold for reference interval estimation (< 120) after applying criteria for vitamin D sufficiency, mineral homeostasis, and age- and sex-specific alkaline phosphatase. Among 155 participants without a history of disease, not using dietary supplements, not pregnant, and with an estimated glomerular filtration rate ≥ 60 mL/min/1.73 m², the unweighted and survey-weighted 2.5th–97.5th reference intervals of PTH were 21.8–65.0 pg/mL and 20.5–67.7 pg/mL, respectively, when vitamin D status and serum calcium, magnesium, and phosphate levels were not considered. CONCLUSIONS: Future population-based studies incorporating broader age ranges and comprehensive biochemical profiling are needed to refine population- and assay-specific PTH reference intervals and to clarify their implications for bone health. CLINICAL TRIAL NUMBER: Not applicable.