What laboratory tests should I order to assess a patient's nutritional status?

Laboratory Tests for Nutritional Status Assessment

For comprehensive nutritional status assessment, order a complete blood count, comprehensive metabolic panel (including albumin), iron studies (ferritin and transferrin saturation), vitamin B12, folate, vitamin D (target ≥75 nmol/L), and lipid profile as your initial core panel. 1

Core Laboratory Panel (Order for All Patients)

Hematologic and Protein Markers

• Complete blood count to assess for anemia, total lymphocyte count (reflects protein status and immune function), and overall hematologic status 1, 2
• Serum albumin should be measured every 3 months in at-risk patients, though recognize it reflects disease severity and inflammation more than acute nutritional status 3, 1
• Pre-albumin or retinol-binding protein are superior to albumin for monitoring because their shorter half-lives better reflect recent nutritional changes and improving status 2

Metabolic Assessment

• Comprehensive metabolic panel including electrolytes (sodium, potassium, chloride), liver enzymes, renal function (creatinine, BUN), calcium, magnesium, and phosphate 1, 2
• Lipid profile (triglycerides, LDL, HDL, total cholesterol) should be obtained, as dyslipidemias are common in malnutrition 3, 1

Essential Micronutrients

• Vitamin B12 and folate must be checked to identify deficiencies causing megaloblastic anemia and neurological complications 1, 4
• Vitamin D levels should be assessed, with sufficiency defined as ≥75 nmol/L 1
• Iron studies (serum ferritin and transferrin saturation) are essential for evaluating iron status and anemia 3, 1

Extended Micronutrient Panel (Order Based on Clinical Presentation)

When to Order Additional Tests

• Zinc and copper if the patient has unexplained anemia, hair loss, poor wound healing, or taste changes 1
• Selenium if there is chronic diarrhea, metabolic bone disease, unexplained anemia, or cardiomyopathy 1
• Vitamin A if night blindness, xerophthalmia, or protein malnutrition is present 1
• Vitamins E and K in cases of malabsorption or unexplained neuropathy 1
• Thiamine (B1) if rapid weight loss, poor dietary intake, vomiting, alcohol abuse, edema, or neurological symptoms are present 1

Special Population Considerations

• Trace elements and vitamins A, E, D, B12, and folic acid should be measured at 12-month intervals in patients on home parenteral nutrition 3
• Inflammatory markers (C-reactive protein) should be assessed to correctly interpret albumin levels, as inflammation causes albumin to drop independent of nutritional status 1, 5

Monitoring Frequency

Initial Assessment Period

• Every 3 months for patients with severe malnutrition or GFR <30 ml/min per 1.73 m² until stabilized, measuring body weight and serum albumin at minimum 3, 1
• More frequent monitoring (potentially weekly during hospitalization) for unstable patients or those with active complications 3

Long-Term Maintenance

• At least annually for stable patients on established nutritional support 1
• Every 3 months for stable home parenteral nutrition patients, including hematology, liver function tests, creatinine, electrolytes, calcium, magnesium, phosphate, and albumin 3

Critical Interpretation Pitfalls to Avoid

Albumin Misinterpretation

Do not rely solely on albumin as a malnutrition marker—it is more accurately a marker of disease severity and inflammation rather than nutritional status per se 3, 2, 5. Always assess inflammatory markers (CRP, ESR) alongside albumin to properly interpret results 5.

Context-Dependent Abnormalities

• Laboratory abnormalities should be interpreted in clinical context, as some findings may be consequences rather than causes of malnutrition 6
• The pathophysiologic effects of underlying disease, especially in hospitalized patients, will affect interpretation of every laboratory test 5
• Fluid status must be considered when interpreting weight changes and certain laboratory values, particularly in patients with ascites or edema 3, 2

Medication Interference

• Most antibiotics, methotrexate, and pyrimethamine invalidate folic acid and vitamin B12 diagnostic assays 4
• Colchicine, para-aminosalicylic acid, and heavy alcohol intake for longer than 2 weeks produce malabsorption of vitamin B12 4
• Review all medications, as many can contribute to weight changes and nutritional abnormalities 6

Clinical Action Thresholds

When Malnutrition is Identified

If body weight decreases unintentionally by more than 5% or serum albumin decreases by more than 0.3 g/dl or is <4.0 g/dl (Bromo-Cresol-Green assay) or <3.7 g/dl (Bromo-Cresol-Purple assay), evaluate for causes and provide diet assessment and counseling 3.

Specific Deficiency Management

• Iron deficiency anemia in celiac disease typically resolves within 1 year of strict gluten-free diet, though 6% of patients may have persistent IDA requiring supplementation 3
• Vitamin B12 deficiency allowed to progress for longer than 3 months may produce permanent degenerative spinal cord lesions, requiring immediate treatment 4
• Doses of folic acid greater than 0.1 mg per day may mask vitamin B12 deficiency while allowing irreversible neurologic damage to progress 4