Which vitamins can be tested for?

Vitamins That Can Be Tested For

Multiple vitamins can be tested for in clinical practice, with the most commonly tested being vitamin B12, folate, vitamin D, iron, and fat-soluble vitamins (A, E, and K), particularly in patients with specific risk factors or conditions. 1

Commonly Tested Vitamins and Their Testing Methods

Vitamin B12

• Serum vitamin B12 levels are routinely tested in patients with:
  • Symptoms of anemia or neuropathy
  • Small bowel disease or previous resection
  • Post-bariatric surgery patients
  • Inflammatory bowel disease (IBD)
• Testing frequency: Every 3-6 months in high-risk patients, annually in others 1
• Reference range: Deficiency typically defined as <150 pmol/L based on methylmalonic acid levels 2

Folate

• Serum folate testing is indicated for:
  • Patients with macrocytic anemia
  • Patients with IBD or malabsorptive conditions
  • Pregnant women
  • Prior to starting erythropoiesis-stimulating agents (ESAs)
• Testing frequency: Every 3-6 months in high-risk patients, annually in others 1
• Note: Folate deficiency has become rare (<1%) in countries with grain fortification 1

Vitamin D

• 25-hydroxyvitamin D is the standard biomarker for vitamin D status 1
• Testing indicated for:
  • Patients with osteoporosis or bone disorders
  • Malabsorptive conditions
  • Chronic kidney disease
  • Post-bariatric surgery patients
• Optimal level: ≥75 nmol/L is considered sufficient 1
• Testing method: LC-MS/MS is the gold standard methodology 1
• Testing frequency: Every 3-6 months initially, then annually 1

Iron

• Iron status testing includes:
  • Serum ferritin
  • Transferrin saturation
  • Complete blood count
• Particularly important in IBD patients, who should be screened every 3 months if symptomatic 1, 3
• Testing frequency: Every 3 months in high-risk patients, annually in others 1

Fat-Soluble Vitamins

Vitamin A

• Testing indicated for:
  • Patients with steatorrhea
  • After malabsorptive bariatric procedures
  • Patients with night blindness
• Testing frequency: Every 3 months initially, then annually once stable 1

Vitamin E

• Testing indicated for:
  • Patients with malabsorptive conditions
  • Unexplained anemia or neuropathy
  • Post-bariatric surgery patients (malabsorptive procedures)
• Testing frequency: At least annually following malabsorptive procedures 1

Vitamin K

• Measured via:
  • Vitamin K1 levels
  • PIVKA-II (Protein Induced by Vitamin K Absence)
  • Prothrombin time (as a functional test)
• Testing indicated for patients with malabsorptive conditions 1
• Testing frequency: At least annually following malabsorptive procedures 1

Special Populations Requiring Vitamin Testing

Inflammatory Bowel Disease Patients

• Regular monitoring of vitamin B12, folate, iron, and vitamin D 1
• Other micronutrients to consider: vitamins K, A, C, B6, B1, selenium, and zinc 1

Post-Bariatric Surgery Patients

• Comprehensive vitamin panel recommended:
  • B12, folate, iron, vitamin D, calcium
  • Vitamins A, E, K (especially after malabsorptive procedures)
  • Zinc, copper
• Testing frequency: 3,6, and 12 months in the first year, then annually 1

Celiac Disease Patients

• Testing for vitamin D, folate, and vitamin B12 deficiencies 1
• Additional testing for vitamins A, E, K if symptoms suggest deficiency 1

Pregnant Women

• Higher requirements for iron, folate, and vitamin D 1, 3
• Regular monitoring recommended, especially post-bariatric surgery 1

Clinical Pitfalls in Vitamin Testing

1. Vitamin D testing variability: Different assay methods may vary by 10-20%, affecting classification of deficiency 1

2. Vitamin B12 interpretation: Deficiency may be present despite normal serum levels; methylmalonic acid may be a better functional marker 2

3. Folate masking B12 deficiency: High folate intake can mask hematological manifestations of B12 deficiency 1

4. Seasonal variation: Vitamin D levels show strong seasonal variation with lowest levels after winter 1

5. Inflammation effect: Vitamin D may act as a negative acute-phase reactant, with levels decreasing during inflammation 1

By understanding which vitamins can be tested and when testing is appropriate, clinicians can better identify and address nutritional deficiencies that impact patient morbidity, mortality, and quality of life.