vitamin D (25 hydroxy vitamin D) TEST

Clinical significance:

Vitamin D regulates calcium and phosphorus levels in body and mineralization of bones. 25hydroxy vitamin D is major storage form of vitamin D in human body .25 hydroxy vitamin D is metabolized in kidney to its active form 1,25 dihydroxy vitamin D (1,25-OHD).

Vitamin D deficiency in adults results in chronic muscle pain, osteomalacia ,reduced bone mass and increased risk of bone fractures. In children, vitamin D deficiency can lead to impaired bone development, growth retardation, and an increased risk of rickets.

Clinical utility

1. Diagnosis of vitamin D deficiency.
2. Differential diagnosis of hyperparathyroidism.
3. Diagnosis and monitoring of rickets and osteomalacia.
4. Monitoring vitamin D replacement therapy and  prevention of vitamin D toxicity.

Interpretation

Decreased vitamin D levels are seen in

Increased vitamin D levels (toxicity) are seen in vitamin D excessive consumption

Limitations

This test may exhibit interference when sample is collected from person who is consuming high dose of biotin (>5mg/day).patients should be cautioned to stop biotin consumption atleast 8 hours prior to collection of sample.

In rare cases heterophilic antibodies in serum can react with reagent immunoglobulin and cause intereference in results,

particularly seen in persons exposed to animals and animal serum products .

Reflex test: Serum calcium, PTH

Implications of vitamin D deficiency in pediatric age group

Rickets: Severe vitamin D deficiency can result in rickets, a condition characterized by weakened, soft, and deformed bones. It can lead to skeletal deformities, delayed growth, and difficulty in walking.

image credit –https://www.aafp.org/pubs/afp/issues/2006/0815/p629.html

Muscle weakness and pain can result from vitamin D deficiency. Children may experience muscle aches and difficulty with physical activities.

Dental Health Issues: Insufficient vitamin D can affect dental health, leading to tooth decay (cavities) and delayed tooth eruption.

Implications of vitamin D deficiency in adults

Osteoporosis: Without sufficient vitamin D, calcium absorption is impaired. Over time, this can lead to weaker bones and an increased risk of osteoporosis, a condition characterized by brittle and porous bones that are more prone to fractures.

Muscle Weakness and Pain

Immune Function: Vitamin D plays a role in immune function, and its deficiency may compromise the body’s ability to defend against infections. Some studies suggest a link between vitamin D deficiency and an increased susceptibility to respiratory infections and autoimmune diseases.

Autoimmune Diseases: Vitamin D has immunomodulatory effects, and its deficiency may contribute to the development or exacerbation of autoimmune diseases, such as rheumatoid arthritis and SLE.Vitamin D deficiency (low serum levels of 25(OH)D) is prevalent in multiple autoimmune diseases, e.g. Multiple Sclerosis, Type 1 DM, and SLE.

Reference:

Fischbach’s a manual of laboratory and diagnostics tests.

Yang CY, Leung PS, Adamopoulos IE, Gershwin ME. The implication of vitamin D and autoimmunity: a comprehensive review. Clin Rev Allergy Immunol. 2013 Oct;45(2):217-26. doi: 10.1007/s12016-013-8361-3. PMID: 23359064; PMCID: PMC6047889.