Terminology of Vit-D : Vitamin D2
Vitamin D3
Calcidiol (25-hydroxy-vitamin D)
Calcifidiol (25-hydroxy-vitamin D)
Calcitriol (1,25 dihydroxy-vitamin D)
Formal name: 25-hydroxy-vitamin D
1,25 dihydroxy-vitamin D
25-hydroxycholecalciferol.
The main role of Vitamin D is:
To help regulate the absorption of calcium, phosphorus, and (to a lesser extent) magnesium.
Vitamin D is vital for the growth and health of bone; without it, bones will be soft, malformed, and unable to repair themselves normally, resulting in diseases called rickets in children and osteomalacia in adults.
Vitamin D has also been implicated in the regulation of autoimmunity, metabolic function, and cancer prevention.
Why Get Tested?
To determine if you have a vitamin D deficiency;
To determine if your vitamin D supplementation level is appropriate, if you are receiving vitamin D therapy
.
When to Get Tested?
If you have an abnormal calcium, phosphorus, and/or parathyroid hormone level,
If you have evidence of bone disease or bone weakness,
If your doctor suspects that you might have vitamin D deficiency,
If you are going to start drug treatment for osteoporosis, or to monitor treatment of vitamin D deficiency;
Sample Required?
A blood sample drawn from a vein in the patient’s arm.
What is being tested?
There are two forms of vitamin D that can be measured in the blood:
25-hydroxyvitamin D [25(OH)D]
1,25-dihydroxyvitamin D [1,25(OH)(2)D]
Vitamin D comes from two sources:
Endogenous, which is produced in the skin on exposure to sunlight
Exogenous, which is ingested in foods and supplements.
Good Sources : Poor sources :
Milk
Egg
Fish
Fish oil
Rice
corn
The chemical structures of these types of vitamin D are slightly different, and they are named vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
The D2 form is found in foods and in most vitamin preparations and supplements.
Vitamin D3 is the form produced in the body and is also used in some supplements.
Vitamin D2 and D3 are equally effective.
Recommended daily allowances for Vit-D :
Age (years) RDA (g/day)
0-1 7.5-10
1-24 10
>25 5
Pregnant/lactation 10
<20 nm/L Deficiency
20-47 nm/L Insufficient
47-147 nm/L Sufficient (Normal)
>147 nm/L Potential intoxicated
25-hydroxyvitamin D
Low blood levels of 25-hydroxyvitamin D may mean that:
You are not getting enough exposure to sunlight
You are not getting enough dietary vitamin D to meet your body’s demand
There is a problem with its absorption from the intestines.
Occasionally, drugs used to treat seizures, particularly phenytoin (Dilantin), can interfere with the production of 25-hydroxyvitamin D in the liver.
High blood levels of 25-hydroxyvitamin D usually reflect excess supplementation from vitamin pills or other nutritional supplements.
1,25-dihydroxyvitamin D
Low levels of 1,25-dihydroxyvitamin D can be seen in kidney disease and are one of the earliest changes to occur in persons with early kidney failure.
High levels of 1,25-dihydroxyvitamin D may occur when there is excess parathyroid hormone or when there are diseases, such as sarcoidosis or some lymphomas, that can make 1,25-dihydroxyvitamin D outside of the kidneys.
Methods of Vit-D measurement :
HPLC [High performance liquid chromatography]
Radio Immunoassay
ELIZA [ Enzyme-linked immunosorbent assay ]
ICMA [ Immunochemiluminometric assay ]
UV absorption
References
1. Henry’s clinical diagnosis and management
by : Laboratory methods
22nd Edition-21012
2. Fundamentals of clinical biochemistry
by : Tietz
3. The vitamins – Fundamental aspects in nutrition and health
by: Gerald F. Combs JR.
4. Harrison's
5. Davidson’s