Vitamin D LCMS Test (D2 & D3)
What is a vitamin D LC-MS/MS test?
Vitamin D is measured in the blood as 25-hydroxyvitamin D, or 25(OH)D — the circulating storage form, and the best indicator of how much vitamin D your body actually holds. It arrives in two forms. D3 (cholecalciferol) is what your skin makes from sunlight and what most supplements contain. D2 (ergocalciferol) comes from fortified foods, some prescription doses, and most vegan supplements.
Most laboratories measure vitamin D with an automated immunoassay, which uses antibodies to bind the molecule. It is fast and inexpensive, but different immunoassays can return noticeably different numbers on the same sample, and some handle D2 poorly.
LC-MS/MS — liquid chromatography with tandem mass spectrometry — separates the molecules physically and identifies them by mass rather than by antibody binding. It is the reference method used to calibrate and standardise vitamin D measurement internationally, and the Royal College of Pathologists of Australasia describes it as having the highest sensitivity and specificity of the available methods.
Do you need this test, or the standard one?
For most people, the standard Vitamin D Test at $55 is the right test. The RCPA position is that an assay measuring 25OH-D3 alone is adequate in Australia and New Zealand, because D3 is the usual supplement form here — so for a straightforward "am I low?" question, the extra precision doesn’t change what you or your doctor would do.
This test is worth the difference when:
- You take a D2 or vegan supplement, or a prescribed high-dose ergocalciferol, and want to know whether it is actually raising your levels
- Your previous results have been inconsistent or sat just around the cut-off, and you want a number you can trust
- You are tracking your level over time and need each result to be comparable with the last
- A practitioner has asked for D2 and D3 reported separately
- You are building a detailed nutritional baseline where precision matters more than cost
What's included
You’ll receive a report showing 25(OH)D2, 25(OH)D3 and your total 25(OH)D in nmol/L, each against its reference interval, with a plain-English summary and suggested next steps. The Australian benchmark is a total 25(OH)D above 50 nmol/L at the end of winter. Levels fall over the colder months, so the time of year matters when reading a result: a level of 55 nmol/L in late summer is a different picture from the same number in September, because winter will take it lower.
Test instructions
You’ll receive your finger prick blood spot test kit and instructions in the mail. There is no need to visit a collection centre.
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Common Questions
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