Book Vitamin D-1, 25 Dihydroxy Test

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The functional form of vitamin D found inside the body is vitamin D-1,24 dihydroxy, sometimes referred to as calcitriol. The fundamental role of vitamin D, a fat-soluble nutrient, is to facilitate calcium and phosphorus absorption from the intestines, which support bone health. Vitamin D is essential for sustaining several elements of general health.

In addition to its role in bone health, 1,25-dihydroxy vitamin D also serves the following purposes:

Calcium Regulation: It controls the amount of calcium and phosphorus in the blood by encouraging their storage in bones and improving their absorption from the intestines.

Support for the Immunological System: According to research, vitamin D affects immunological responses by regulating the immune system.

Cellular Growth and Differentiation: Vitamin D has an impact on cell growth and differentiation, which are essential for keeping tissues healthy.

Vitamin D helps control inflammation, potentially lowering the risk of chronic diseases by affecting hormone secretion and function.



Weakened Bones: Low 1,25-dihydroxy vitamin D levels can increase fracture and osteoporosis risks. 

Muscle Weakness: Inadequate Vitamin D leads to muscle weakness and pain.

Fatigue: A deficiency may cause fatigue and reduced energy.

Joints Discomfort: Low levels contribute to joint pain.

Weakened Immunity: Imbalances raise infection vulnerability.

Mood Changes: Low vitamin D is related to mood disorders.

Hair and Skin Issues: Deficiency affects hair and skin health.

Digestive Problems: Imbalances impact gut health.



It is important to remember that fasting guidelines could change based on the precise test being run. As a result, it is advised that you speak with your healthcare professional or refer to the precise instructions that the laboratory has supplied. Maintaining adequate water levels also supports general well-being and health while contributing to reliable test findings.



*Reference range may vary depending on equipment used by labs. Consult your referring doctor for proper interpretation of test results.







<16 years

24 – 86 pg/mL

24 – 86 pg/mL

16 years or older

18 – 64 pg/mL

18 – 78 pg/mL



Consult a doctor: seek medical advice for low vitamin D (1,25-dihydroxy) levels. Tailored steps can be recommended.

Supplementation: Follow doctor-prescribed vitamin D supplements meticulously.

Diet Enrichment: Include vitamin D-rich foods like fish, dairy, eggs, and mushrooms.

Sun Exposure: Moderate sun exposure, guided by a doctor, helps. Prevent excessive exposure.

Regular Testing: Monitor progress with scheduled follow-up tests.

Medication Review: Discuss medications with your doctor, as some affect vitamin D.

Healthy Lifestyle: Maintain a balanced diet, exercise, and stress management.

Medical Guidance: Adhere to healthcare providers' advice and avoid self-prescribing supplements.



Functions, Testing & Clinical Significance

Vitamin D Overview: Vitamin D is a group of fat-soluble sterols with hormone-like functions, derived from dietary sources (plants and animals) or endogenously through skin exposure to UV light. 

Testing for Vitamin D Status: In cases of renal disease or hypercalcemia, assessing 1,25-dihydroxy vitamin D (DHVD) is necessary; otherwise, the preferred initial test is 25-hydroxyvitamin D (25HDN) to accurately gauge vitamin D stores. 

Synthesis and Storage: Vitamin D compounds, such as 25-hydroxyvitamin D2 and D3, are derived from diet and skin exposure. 25HDN, the main vitamin D reservoir, is formed in the liver and stored in adipose tissue, later converted to active DHVD.

Biological Activity: DHVD, the active form, influences calcium absorption, bone health, and gene expression through nuclear receptors. It's regulated by factors like PTH and serum calcium levels.

Multiple Functions: DHVD has broader effects beyond bone health, impacting gene expression in immune cells, muscle, vasculature, and reproductive organs.

Clinical Implications: DHVD levels vary in conditions like hypoparathyroidism, chronic renal failure, hyperparathyroidism, and granulomatous diseases. In certain cases, hypercalcemia with low PTH might be mediated by nonregulated 1-alpha hydroxylase.

24,25D Assessment: In hypercalcemia cases unrelated to PTH, assessing 24,25D and CYP24A1 mutations can provide insights.

Diagnostic Challenges: Considerations include vitamin D intoxication, CYP24A1 deficiency, and genetic factors.


ALIASES (Other names that describe the test. Synonyms.)


1,25-Dihydroxy Vitamin D


1,25-Dihydroxyvitamin D

1,25-Dihydroxyvitamin D3


D, 1-25 Dihydroxy, Vitamin

Vit D 1,25



May be useful for evaluating calcium metabolism in individuals with hypercalcemia or renal failure in addition to Vitamin D, 25-Hydroxy testing. Test is not appropriate for diagnosing vitamin D deficiency or insufficiency.



[QUESTION] What is Vitamin D, 1,25-dihydroxy?

[ANSWER] Vitamin D (1,25-dihydroxy), also known as calcitriol, is the active form of vitamin D in the body. It plays a crucial role in various physiological functions beyond bone health.


[QUESTION] Why might testing for 1,25-dihydroxy vitamin D be needed?

[ANSWER] Testing for 1,25-dihydroxy vitamin D is recommended in cases of renal disease or hypercalcemia to accurately assess vitamin D status.


[QUESTION] What is the primary initial test for vitamin D status?

[ANSWER] The preferred initial test is the 25-hydroxyvitamin D (25HDN) test in serum. It provides a more accurate reflection of the body's vitamin D stores.


[QUESTION] How does the body make vitamin D?

[ANSWER] Vitamin D compounds can be created endogenously through the skin after exposure to UV light. These sources include 25-hydroxyvitamin D2 from plants and 25-hydroxyvitamin D3 from animal products. 


[QUESTION] What function does 25HDN serve in the human body? 

[ANSWER] The primary storage and transportation form of vitamin D is 25HDN. It circulates in a firmly bound state and is stored in adipose tissue. Later, it is changed into 1,25-dihydroxy vitamin D, which is the active form.


[QUESTION] How is 1-alpha-hydroxylation carried out? 

[ANSWER] Parathyroid hormone (PTH), especially in the kidneys, regulates 1-alpha-hydroxylation. It changes 25HDN into 1,25-dihydroxy vitamin D, which is the active form. 


[QUESTION] What is 1,25-dihydroxy vitamin D used for? 

[ANSWER] Vitamin 1,25-dihydroxy D controls the amounts of calcium and phosphorus in the body, promotes bone health, regulates immunological function, affects gene expression, and has an impact on many body tissues.  


[QUESTION] How can DHVD impact bone health and calcium absorption? 

[ANSWER] DHVD increases calcium mobilization or deposition in bones and enhances calcium absorption in the intestines. It also affects the renal reabsorption of calcium and phosphate. 


[QUESTION] What clinical ramifications do DHVD values have? 

[ANSWER] Conditions like hypoparathyroidism and chronic renal failure can cause low DHVD levels. Elevated levels may be seen in conditions like non-regulated 1-alpha hydroxylase disorders or hyperparathyroidism. 


[QUESTION] How is the 1,25-dihydroxy metabolism of vitamin D controlled? 

[ANSWER] The CYP24A1 enzyme controls metabolism and changes 25HDN into the inactive form of vitamin D, 24,25-dihydroxy vitamin D. This process prevents the overproduction of DHVD and its potential toxicity.



Component Test Code*

Component Chart Name



Vitamin D, 1,25-Dihydroxy


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