Functional reference limit: objectively defining the physiological relationship between serum vitamin D and...

Area of Science:

• Biostatistics
• Biomarker Discovery
• Clinical Chemistry

Background:

• Functional reference limits are crucial for interpreting biomarker data.
• Existing methods may lack objectivity in defining these limits.
• The relationship between vitamin D and parathyroid hormone is a key indicator of bone health.

Purpose of the Study:

• To develop and validate a statistical framework for objectively defining functional reference limits.
• To establish a functional reference limit for serum 25-hydroxy vitamin D (vitamin D) using parathyroid hormone as a reference biomarker.
• To provide a reproducible method applicable to other biologically related biomarker pairs.

Main Methods:

• Utilized a statistical framework to analyze the homoeostatic relationship between vitamin D and parathyroid hormone.
• Generated scatter plots to identify inflection points (breakpoints).
• Employed normalized data, weighted linear regressions, and a sliding window approach to find the optimal fit and determine the breakpoint.

Main Results:

• Identified a functional reference limit (breakpoint) for vitamin D at 28 nmol/L.
• Achieved a mean squared residual of 0.0022 with 800 fixed concentration intervals.
• Demonstrated the framework's ability to objectively define functional reference limits.

Conclusions:

• The proposed statistical framework objectively defines functional reference limits.
• The method provides a reliable breakpoint for vitamin D, crucial for clinical interpretation.
• This approach can be extended to other biomarker pairs, enhancing diagnostic accuracy.