Vitamin D3

Vitamin

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No Fasting Required

Details

Assesses 25-hydroxyvitamin D levels to determine deficiency, affecting bone strength and immune function.

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Vitamin D3 Test Information Guide

Why is it done?
- Measures serum 25-hydroxyvitamin D [25(OH)D] levels, which reflect total body vitamin D stores from both dietary sources and sun exposure
- Evaluates risk for bone disorders including osteoporosis, osteomalacia (soft bones), and rickets in children
- Assesses calcium metabolism and parathyroid function regulation
- Investigates symptoms of bone pain, muscle weakness, and chronic fatigue
- Screens patients at risk for deficiency: limited sun exposure, malabsorption disorders, dietary restrictions, dark skin pigmentation in northern climates
- Evaluates immune function, cardiovascular health, and cancer risk assessment
- Monitors patients on vitamin D supplementation or those with chronic kidney/liver disease
- Typically performed during routine screening, annual physical examinations, or when clinically indicated
Normal Range
- Optimal/Sufficient: 30-100 ng/mL (75-250 nmol/L)
- Insufficient: 20-29 ng/mL (50-74 nmol/L)
- Deficient: Below 20 ng/mL (below 50 nmol/L)
- Potentially Excessive: Above 100 ng/mL (above 250 nmol/L)
- Units: Measured in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L)
- Normal Result: Indicates adequate vitamin D status for bone health, calcium absorption, and optimal immune and cardiovascular function
- Abnormal Result: Low levels require intervention; high levels may indicate toxicity requiring medical evaluation
- Note: Reference ranges may vary slightly between laboratories; always refer to the specific lab's reference values
Interpretation
- Low Vitamin D (Deficiency/Insufficiency):
  - May cause or contribute to bone loss, osteoporosis, increased fracture risk, and muscle weakness
  - Associated with poor calcium absorption and secondary hyperparathyroidism
  - May increase susceptibility to infections and autoimmune disorders
  - In children: can lead to rickets with skeletal deformities and developmental delays
  - Symptoms may include bone/muscle pain, fatigue, mood disturbances, and increased infections
- Normal Vitamin D:
  - Adequate for bone health, normal calcium homeostasis, and proper immune function
  - Supports normal muscle function and neurological health
  - Associated with reduced cardiovascular and certain cancer risks
- High Vitamin D (Toxicity):
  - Typically occurs from excessive supplementation (not from sun exposure or diet alone)
  - Can cause hypercalcemia leading to nausea, vomiting, kidney stones, and impaired kidney function
  - May increase bone resorption, paradoxically weakening bones despite high levels
  - Symptoms include fatigue, headache, weakness, and calcification of soft tissues
- Factors Affecting Readings:
  - Sun exposure (varies seasonally, latitude, and skin pigmentation)
  - Dietary intake (fatty fish, egg yolks, fortified milk products)
  - Malabsorption disorders (celiac disease, Crohn's disease, cystic fibrosis)
  - Medications (anticonvulsants, glucocorticoids, antiretrovirals) affecting metabolism
  - Kidney and liver disease impairing activation to active forms
  - Age (decreased skin synthesis with aging; absorption efficiency varies)
  - Obesity (vitamin D sequestration in adipose tissue)
  - Supplementation dosage and duration
Associated Organs
- Primary Organ Systems:
  - Skeletal System: Bones and cartilage (vitamin D essential for calcium absorption and bone mineralization)
  - Renal System: Kidneys (convert 25(OH)D to active 1,25-dihydroxyvitamin D; kidney disease impairs activation)
  - Hepatic System: Liver (hydroxylates vitamin D to 25-hydroxyvitamin D, the measured form)
  - Endocrine System: Parathyroid glands (vitamin D regulates PTH secretion)
  - Gastrointestinal System: Small intestine (site of calcium and phosphate absorption)
  - Immune System: Lymphocytes and macrophages (vitamin D modulates immune responses)
  - Muscular System: Skeletal and cardiac muscle (vitamin D essential for muscle function and strength)
  - Cardiovascular System: Blood vessel endothelium (vitamin D modulates vascular function)
- Conditions Associated with Abnormal Results:
  - Osteoporosis and osteopenia (decreased bone mineral density)
  - Rickets (nutritional or hereditary forms with skeletal deformities)
  - Osteomalacia (adult soft bone disease causing bone pain and weakness)
  - Chronic kidney disease and renal osteodystrophy
  - Liver cirrhosis and hepatic dysfunction
  - Hypoparathyroidism and hyperparathyroidism (calcium regulation disorders)
  - Celiac disease, Crohn's disease, and other malabsorption syndromes
  - Sarcoidosis and other granulomatous diseases
  - Recurrent infections and autoimmune conditions (lupus, rheumatoid arthritis)
  - Type 1 and Type 2 diabetes mellitus
  - Cardiovascular disease and hypertension
  - Certain malignancies (breast, prostate, and colorectal cancers)
- Potential Complications from Abnormal Results:
  - Low levels: Increased fracture risk, impaired muscle function, falls in elderly, immune dysfunction, possible increased cancer risk
  - High levels: Hypercalcemia leading to kidney damage, kidney stones, cardiac arrhythmias, and soft tissue calcification
Follow-up Tests
- Tests Based on Low Vitamin D Results:
  - Serum calcium (assess calcium metabolism and hypocalcemia risk)
  - Serum phosphate (evaluate phosphorus balance)
  - Parathyroid hormone (PTH) level (assess secondary hyperparathyroidism)
  - Alkaline phosphatase (marker for bone turnover)
  - Bone mineral density (DEXA scan) for osteoporosis/osteopenia assessment
  - Renal function tests (creatinine, BUN, eGFR) if considering supplementation
  - Liver function tests if liver disease suspected
  - Celiac serology if malabsorption suspected
- Tests Based on High Vitamin D Results:
  - Serum calcium (assess for hypercalcemia)
  - 24-hour urine calcium (evaluate hypercalciuria and kidney stone risk)
  - Renal function tests (creatinine, BUN, eGFR for kidney damage assessment)
  - PTH level (assess suppression)
  - Serum and urine phosphate levels
- Monitoring and Follow-up Frequency:
  - Initial deficiency: Retest 8-12 weeks after starting supplementation to assess response
  - Chronic kidney disease: Monitor every 3-6 months depending on stage
  - On vitamin D supplementation: Annual testing to maintain optimal levels
  - Osteoporosis patients: May retest annually or as clinically indicated
  - Post-supplementation dose adjustment: Retest 8 weeks after any dose change
  - Screening in asymptomatic healthy adults: Every 3-5 years (or per guidelines)
- Complementary Tests:
  - Bone turnover markers (P1NP, CTX) to assess bone remodeling
  - Magnesium level (required for vitamin D metabolism and activation)
  - 1,25-dihydroxyvitamin D (active form, ordered in specific clinical situations)
  - Vitamin D-binding protein (DBP) in complex cases
Fasting Required?
- Fasting Required: No
- Vitamin D3 testing does not require fasting. Food and beverages do not affect the accuracy of results
- Special Preparation:
  - No special preparation needed prior to blood draw
  - Can eat and drink normally before the test
  - Standard blood draw procedure applies (arm accessed for venipuncture)
- Medications to Report (Not Required to Avoid):
  - Continue vitamin D supplements as prescribed (report dose to healthcare provider)
  - Continue all medications normally; medications do not interfere with test
  - Inform phlebotomist and provider of any anticonvulsants, glucocorticoids, or other vitamin D-affecting medications for context
- Patient Instructions:
  - Wear loose, comfortable clothing with easily accessible arm for blood draw
  - Arrive well-hydrated; drink adequate fluids to facilitate blood draw
  - Bring photo ID and insurance card to laboratory
  - Inform phlebotomist of any bleeding disorders or difficulties with blood draws
  - Report any recent vitamin D supplementation dose changes to healthcare provider
  - Test can be performed at any time of day; timing is not critical

How our test process works!