Table 2. Advantages and limitations of MS-based methods and immunoassays for vitamin D measurement.

Method	Advantages	Limitations
MS-based	high sample volume (LC-MS) availability of reference measurement procedures separation of vitamin D metabolites allows the inclusion of stable isotope-labelled standards	not intended for routine clinical samples analysis not fully automated complex and expensive instrumentation no distinction between epimers
Immunoassays	high sensitivity reduced sample volume fully automated	cross-reactivity with other vitamin D metabolites (e.g., D2 vs. D3) measurement of free 25(OH)D requires VDBP displacement (proprietary methods)
LC-MS – liquid chromatography-mass spectrometry. VDBP - vitamin D binding proteins.