Vitamin tests

Explore vitamin D, vitamin B12 and Active B12, and the names and units labs print.

Explore vitamins

Vitamin B12 and Active B12: two different tests with similar names

A total B12 measures all of it in circulation; Active B12 measures only the fraction available to your cells. They are not interchangeable, and reports rarely say which you had.

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Test explainer

Vitamin D (25-OH)

Reported in ng/mL · nmol/L.

Test explainer

Vitamin B12

Reported in pg/mL · pmol/L.

Test explainer

Active B12

Reported in pmol/L.

Reading the report

Guide

What the H and L flags on a lab report actually assert

A flag compares your number to the range printed beside it on that page — nothing more. What it does not tell you, and why healthy people collect them.

Guide

Why the same blood test has different "normal" ranges at different labs

Reference intervals are built from each lab's own population and equipment, which is why two labs can print different ranges for the same sample.

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