Vitamin D

S -D-25 KL 1220

Vitamin D is a fat-soluble vitamin that forms through the synthesis of 7-dehydrocholesterol in the skin, catalyzed by exposure to UV light from the sun. Some portion of vitamin D is also sourced from dietary elements such as mushrooms and fish. Following this, the liver initiates hydroxylation, transforming it into 25-OH vitamin D (calcidiol), which constitutes the predominant circulating form in the bloodstream. The biologically active variant, named 1,25-dihydroxy vitamin D (calcitriol), arises via 1-hydroxylation within the kidneys. Calcitriol operates as a hormone, influencing calcium and phosphorus metabolism, thereby augmenting their absorption. Beyond this pivotal role, vitamin D contributes to numerous other aspects of holistic well-being, with comprehensive research delving into its potential to prevent various ailments. It is noteworthy that the body inherently generates the active form of calcitriol (1,25-dihydroxy vitamin D).


Regularly assessing vitamin D treatment is crucial, especially for individuals at higher risk, including elderly individuals, pregnant women, children under the age of 2 who are not receiving vitamin D supplements, and people with restricted sunlight exposure (such as inpatients).


Blood sample. Normal eating and drinking is allowed.

No vitamin D supplements 12 hours before sampling.


1.5 mL (minimum 1 mL) of serum

Storage and delivery

Delivery at room temperature on the sampling day if it arrives the next day (Mon-Fri). Can be stored refrigerated over the weekend, ship at room temperature.


Liquid chromatography (HPLC)

Turnaround time

5 – 10 weekdays

Reference ranges

below 25 nmol/Lserious deficiency
below 50 nmol/Ldeficiency
50-75 nmol/Lgenerally regarded as sufficient concentration
75-120 nmol/Lrecommended concentration
over 375 nmol/Ltoxic concentration
The interpretation is based on the Osteoporosis Treatment Recommendation (December 8, 2020)


Last update 8.8.2023