What vitamin labs should be ordered for a patient suspected of malnutrition?

Laboratory Tests for Diagnosing and Managing Malnutrition

For patients suspected of malnutrition, a comprehensive laboratory assessment should include complete blood count, comprehensive metabolic panel, vitamin levels, and specific micronutrient testing based on clinical presentation. 1

Core Laboratory Tests

• Complete Blood Count (CBC): Assess for anemia and total lymphocyte count, which reflects protein status and immune function 1
• Comprehensive Metabolic Panel: Including electrolytes, liver enzymes, and renal function tests to evaluate organ function and electrolyte balance 1
• Serum Proteins: Albumin and pre-albumin (transthyretin) to assess protein status, though these can be affected by inflammation 1

Essential Vitamin and Mineral Tests

• Vitamin B12 and Folate: Check serum levels to identify deficiencies that can cause megaloblastic anemia and neurological complications 2

  • Important: Vitamin B12 deficiency must be ruled out before treating folate deficiency, as folate supplementation can mask B12 deficiency while allowing neurological damage to progress 3

• Vitamin D: Check serum 25-hydroxyvitamin D levels, with levels ≥75 nmol/L considered sufficient 2

  • Vitamin D deficiency is highly prevalent in malnourished patients and associated with higher mortality 4

• Iron Studies: Complete with serum ferritin, transferrin saturation to assess iron status 2

  • Note that ferritin is an acute phase reactant; in inflammation, levels ≥50 μg/L may still indicate iron deficiency 2

Additional Micronutrient Testing

• Zinc and Copper: Check serum/plasma levels, particularly if patient presents with unexplained anemia, hair loss, poor wound healing, or changes in taste 2

  • These tests should be monitored together as supplementation of one can affect levels of the other 2

• Selenium: Check serum levels if there is chronic diarrhea, metabolic bone disease, unexplained anemia, or cardiomyopathy 2

• Vitamin A: Consider checking serum levels if patient reports night blindness, xerophthalmia, or has protein malnutrition 2

• Vitamins E and K: Check in cases of malabsorption or if unexplained neuropathy is present 2

Special Considerations

• Inflammatory Markers: C-reactive protein should be measured alongside albumin, as inflammation affects interpretation of nutritional protein markers 1

• Thiamine (B1): Check if rapid weight loss, poor dietary intake, vomiting, alcohol abuse, edema, or neurological symptoms are present 2

• For Children: Additional tests should include triglycerides, calcium, phosphorus, and magnesium 5

Testing Algorithm

1. Initial Assessment:

   • CBC, comprehensive metabolic panel, serum proteins 1
   • Vitamin B12, folate, vitamin D, iron studies 2

2. Based on Clinical Presentation:

   • Unexplained anemia: Check zinc, copper, selenium 2
   • Neurological symptoms: Prioritize B12, thiamine, vitamin E 3, 6
   • Skin/mucosal changes: Check vitamin A, zinc 2, 7
   • Malabsorption/post-bariatric surgery: Check fat-soluble vitamins (A, D, E, K), B12, zinc 2

3. Monitoring Frequency:

   • For severe malnutrition: Monitor every 3 months until stabilized 2
   • For stable patients: Monitor at least annually 2

Common Pitfalls to Avoid

• Relying solely on albumin as a marker of malnutrition (affected by inflammation) 1, 8
• Treating folate deficiency without first ruling out B12 deficiency 3
• Not considering micronutrient deficiencies in patients with normal macronutrient status 9
• Failing to repeat measurements frequently enough in critically ill patients 5

Remember that laboratory tests should be interpreted alongside clinical assessment and anthropometric measurements for a complete nutritional evaluation 1, 5.