Vitamin D Lab Values

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Determine the significance and clinical use of the lab value of Vitamin D in clinical practice.


Lab Test Name:

Vitamin D- 25 Hydroxy



Measurement of Vitamin D circulating in the blood

  • Development and calcification of bones
  • Aids in Ca & Phos absorption
  • Suppresses PTH
  • Inverse relationship with PTH lab
  • Calcidiol, cholecalciferol, ergocalciferol

Vitamin D

  • fat-soluble vitamin
  • synthesized in dermal tissue, and through dietary intake
  • converts to its circulating form by an enzyme produced by the liver
  • Conversion to biologically active form through the kidney.



Presentation of low Vitamin D:

  • S/S Hypocalcemia
  • Medications 
  • Malabsorption
  • Osteoporosis
  • Rickets
  • Osteomalacia


Normal Therapeutic Values:

Vitamin D >20 ng/ml

Criteria to define optimal:

  • Maximal suppression of PTH- when Vitamin D levels in the blood are low, calcium absorption in the intestine suffers and PTH is released (as part of the negative feedback mechanism of hormone production and distribution) thereby increasing the risk of thinning bones, and kidney stones. 
  • Adequate intestinal calcium absorption-in the case of extremely low Vitamin D concentration, Ca absorption decreases through the intestine resulting in hypocalcemia
  • Fracture prevention- stronger bones, fewer falls


  • Serum separator tube


What would cause increased levels?

INCREASED: Vitamin D toxicity

Due to ingestion of massive amounts of calcium


What would cause decreased levels?

DECREASED: Deficiency 

  • <12 ng/ml
  • Medications- glucocorticoids
  • Hospitalization
  • Osteoporosis
  • Limited sun exposure
  • Gastric surgery- removal of portion of the intestines
  • Malabsorption- IBD, celiac, CF, 
  • Kidney and liver disease- decrease in metabolic enzymes that convert Vitamin D to its biologically active form


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Hey everyone. This is Abby with Our lab lesson day covers vitamin D. If it’s written out, you’ll see it as 25 hydroxy D. Let’s get started!


Vitamin D or in chemical terms, 25(OH)D is a measurement of vitamin D circulating in the blood. Vitamin D is essential to the development and calcification of bones. It aids in calcium and phosphorus absorption. It suppresses parathyroid hormone and has an inverse relationship with that lab. It’s also known as Calcidiol. The biggest way that vitamin D is synthesized is through our dermis, through sun exposure with our skin. So, if it has an inverse relationship with PTH and it is essential to calcification of bones and helps with calcium phosphorus absorption, what type of clinical indications or presentations from a patient might we see to take this lab value? I bet you were thinking about calcium, calcium, exactly. Signs and symptoms of hypocalcemia, certain medications in terms of mal-absorption, so this could be a hormonal disorder or a GI disorder, osteoporosis, patients with rickets, and also osteomalacia are indications to take a vitamin D lab. And particularly that’s when it’s low. You can see here, the difference in bone density, here in normal bone tissue, and here in osteoporotic bone tissue. In osteoporosis, calcification of bone suffers, and it becomes spongy and hollowed. If there’s not enough vitamin D, calcification suffers, and that’s where we get osteoporosis. 


Normal therapeutic values are above or equal to 20 nanograms per milliliter. The literature suggests that we want optimal. We’re not really going for high, and we definitely don’t want low. When it’s optimal, it being vitamin D, suppression of PTH is at its max. We want that because PTH is what leaches calcium out of the bones and can lead to osteoporosis. We also want enough vitamin D to maximize calcium absorption in the intestines.It also helps to prevent fracture. Remember, we talked about how it aids in calcification rather, of the bones. This is a lab that’s collected in a serum separator tube. An increased lab value for vitamin D would suggest toxicity. This would be massive values greater than 100 nanograms per milliliter. This would suggest most often an over ingestion of supplementation. It could never be gained from too much sun exposure. A deficiency on the other hand means that there’s less than 12 nanograms per milliliter. This deficiency could be caused by certain medications seen in hospitalized or institutionalized patients. We talked about osteoporosis and even those that have limited sun exposure, as our dermis is the largest or fastest/ best way to absorb, to synthesize vitamin D. We also see it. If someone has had gastric surgery or malabsorptive disorders or, in kidney or liver disease. 


The linchpins for this lesson, when you think vitamin D, think calcium. When you think calcium, you think bones. When we have good strong calcified bones, we have fewer falls. Remember that safety component as part of the ABCs. Now, if it’s greater than or equal to 20 nanograms per milliliter, that’s our optimal range, typically up to about 30 nanograms per milliliter. If that value is increased, it’s going to mean that there’s over supplementation and if it’s decreased, there’s going to be a bone or a GI-related disease or disorder. You all did great on this lesson. It wraps it up here for vitamin D. You can do this! We love you guys. Now go out and be your best self today, and as always, happy nursing!



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