What blood tests are required for a comprehensive nutrition screen in patients of various ages and demographics, including those with a history of gastrointestinal disease or malabsorption?

Blood Tests Required for Nutrition Screening

A comprehensive nutrition screen requires a complete blood count (CBC) and comprehensive metabolic panel (CMP) as the foundational laboratory assessment, supplemented by specific micronutrient tests based on clinical context and risk factors. 1

Core Laboratory Panel (Required for All Patients)

Every nutrition screen should include these essential tests:

• Complete Blood Count (CBC) to assess for anemia, leukopenia, total lymphocyte count (reflecting protein status and immune function), and other hematologic abnormalities 1, 2
• Comprehensive Metabolic Panel (CMP) including:
  • Electrolytes (sodium, potassium, chloride, bicarbonate) 1, 2
  • Glucose 2
  • Calcium 1
  • Liver enzymes (ALT, AST, alkaline phosphatase, bilirubin) 1, 2
  • Renal function tests (BUN, creatinine, eGFR) 1, 2
  • Serum albumin 2

Haematinic Panel (Essential for Most Screens)

These tests identify common nutritional deficiencies:

• Serum ferritin and transferrin saturation for iron status assessment 3, 1, 2
• Vitamin B12 to detect deficiency causing megaloblastic anemia and neurological complications 3, 1, 2
• Folate (folic acid) for assessment of folate deficiency 3, 1, 2

Vitamin D and Bone Health

• Serum 25-hydroxyvitamin D levels, as deficiency is extremely common in at-risk populations (reported up to 99% in some groups) 3
• Parathyroid hormone (PTH) when vitamin D deficiency is present or primary hyperparathyroidism is suspected 3

Critical Interpretation Considerations

Albumin and prealbumin must be interpreted with extreme caution:

• Albumin primarily reflects inflammation and disease severity, NOT nutritional status alone 3, 1, 2
• Always measure C-reactive protein (CRP) alongside albumin to distinguish inflammation from true nutritional deficiency 2
• Hypoalbuminemia in hospitalized patients most commonly reflects acute phase response to inflammation and protein redistribution, not malnutrition 2
• Prealbumin has a shorter half-life and better reflects recent nutritional changes, but is also affected by inflammation 2

Additional Tests Based on Clinical Context

Consider these tests in specific high-risk populations:

For Malabsorption or Bariatric Surgery Patients:

• Vitamin A if night blindness, xerophthalmia, or protein malnutrition present, or before malabsorptive procedures like BPD/DS 3, 2
• Zinc if unexplained anemia, hair loss, poor wound healing, or taste changes present 3, 2
• Copper if unexplained anemia or neurological symptoms present 3, 2
• Selenium if chronic diarrhea, metabolic bone disease, unexplained anemia, or cardiomyopathy present 3, 2
• Vitamins E and K in cases of malabsorption or unexplained neuropathy 2

For Patients with Rapid Weight Loss or High-Risk Behaviors:

• Thiamine (B1) if rapid weight loss, poor dietary intake, vomiting, alcohol abuse, edema, or neurological symptoms present 3, 2
• Magnesium in specific clinical scenarios 3

For Chronic Kidney Disease Patients:

• Lipid profile (triglycerides, LDL, HDL, total cholesterol) 3, 2
• Monitor serum albumin every 3 months in at-risk patients 2

Laboratory Tests Alone Are Insufficient

Critical pitfall to avoid: Laboratory tests must NEVER be used in isolation for nutrition screening 3, 1

The complete nutrition screen requires integration of:

• Validated screening tools (NRS-2002, MUST, MNA-SF, or SGA) 3
• Anthropometric measurements (BMI, weight loss history, mid-upper arm circumference) 3
• Physical examination findings 3
• Dietary intake assessment 3
• Medical and psychosocial history 3

Monitoring Frequency After Initial Screen

Adjust monitoring based on severity:

• Severe malnutrition or critically ill patients: Daily monitoring of electrolytes and glucose during initial stabilization 2
• Stable chronic malnutrition: Every 3 months until stabilized 1, 2
• Long-term parenteral nutrition: Trace elements and vitamins measured at 12-month intervals 1
• Hospitalized patients: Weekly rescreening if initial screen negative 3

Common Pitfalls to Avoid

• Never assume normal BMI excludes malnutrition—sarcopenic obesity and muscle wasting can occur despite normal or elevated BMI 1
• Never rely solely on albumin as a nutritional marker—it primarily reflects inflammation and disease severity 3, 1, 2
• Never interpret weight changes without assessing fluid status—edema and ascites make weight measurements unreliable 2
• Never use laboratory values without validated screening tools—no single parameter has sufficient predictive value alone 2