PTH levels and establishment of reference intervals: Impact of vitamin D and renal function

Parathyroid hormone (PTH) and vitamin D are essential components in mineral metabolism. Our aims were to estimate the thresholds of 25-hydroxyvitamin D [25(OH)D] and estimated glomerular filtration rate (eGFR) that inhibit PTH, establish PTH reference intervals (RIs), and the stratify need based on age and gender.

We conducted a cross-sectional study on participants older than 18 years. Segmented regressions (SR) were performed to determine the thresholds of 25(OH)D and eGFR in relation to PTH levels. Multivariate regression was used to evaluate the associations between PTH and 25(OH)D, gender, age, eGFR, and season. To establish the PTH RIs, extreme percentiles were calculated.

A total of 2794 subjects were analyzed (women, 77.56%). Multivariate regression indicated that age, gender, 25(OH)D, and eGFR explained PTH variation. SR demonstrated that PTH stabilized when eGFR>46.64mL/min/1.73m², and PTH increased when 25(OH)D was <15.8ng/mL. Stratification by gender and age revealed different RIs, with women and over 70 years showing higher limits.

Our study suggests a stabilization point in PTH with an eGFR>46.64mL/min/1.73m², indicating a significant interaction between renal function and PTH regulation. Additionally, the significant increase in PTH in individuals with 25(OH)D<15.8ng/mL emphasizes the importance of vitamin D in regulation. An association between age and PTH was also evident, particularly a substantial increase after the age of 70. Finally, we established the need to define partitioned RIs for PTH based on age and gender.