What lab work is recommended for patients suspected of malnutrition?

Laboratory Work for Malnutrition Assessment

For patients suspected of malnutrition, obtain a core laboratory panel including complete blood count, comprehensive metabolic panel with electrolytes and liver enzymes, serum albumin with inflammatory markers (C-reactive protein), prealbumin, and iron studies, followed by targeted micronutrient testing based on clinical presentation. 1

Initial Core Laboratory Panel

The baseline assessment should include:

• Complete blood count to evaluate hemoglobin and total lymphocyte count, which reflect protein status and immune function 1, 2
• Comprehensive metabolic panel including electrolytes (sodium, potassium, chloride, calcium, phosphorus, magnesium), liver enzymes (ALT, AST, alkaline phosphatase, bilirubin), and renal function (creatinine, BUN) 1, 3
• Serum albumin measured alongside C-reactive protein or other inflammatory markers (orosomucoids) to distinguish inflammation from true nutritional deficiency 4, 1
• Prealbumin (transthyretin) or retinol-binding protein, which have shorter half-lives and are superior for detecting recent nutritional changes 4, 1, 2
• Lipid profile including triglycerides, total cholesterol, LDL, and HDL 1, 3

Critical Interpretation Pitfall

Do not attribute low albumin solely to malnutrition in hospitalized patients without assessing inflammatory markers, as hypoalbuminemia most commonly reflects acute phase response to inflammation and protein redistribution, not pure malnutrition. 1, 3 Albumin is more accurately a marker of disease severity and inflammation rather than nutritional status. 1

Essential Micronutrient Assessment

The initial micronutrient panel should include:

• Vitamin B12 and folate to identify deficiencies causing megaloblastic anemia and neurological complications 1
• Vitamin D levels, with sufficiency defined as ≥75 nmol/L 1
• Iron studies including serum ferritin and transferrin saturation to evaluate iron status and anemia 1

Extended Micronutrient Testing Based on Clinical Presentation

Additional testing should be guided by specific clinical features:

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

Risk Stratification Tools

Use validated risk scores combining multiple parameters rather than relying on isolated laboratory values, as the predictive value of each individual parameter alone is insufficient. 4, 1 Available tools include:

• Prognostic inflammatory and nutritional index 4, 1
• Nutritional risk index 4, 1
• Prognostic nutritional risk 4
• Aid for decision for nutritional support score 4

Monitoring Frequency Algorithm

The frequency of laboratory monitoring depends on malnutrition severity:

• Severe malnutrition or critically ill patients: Daily monitoring of electrolytes and glucose during initial stabilization 1, 3
• Stable patients with chronic malnutrition: Every 3 months measuring body weight and serum albumin at minimum until stabilized 1
• Long-term parenteral nutrition patients: Trace elements and vitamins (A, E, D, B12, folic acid) at 12-month intervals 1
• Annual monitoring for stable patients 1

Special Considerations for Refeeding Syndrome

When initiating feeding in malnourished patients, check electrolytes (phosphate, potassium, magnesium) at least daily to prevent refeeding syndrome. 1 Screen for refeeding syndrome risk if patients have:

• BMI <16 kg/m² 4
• Unintentional weight loss >15% in 3-6 months 4
• Little or no intake for >10 days 4
• Low potassium, phosphate, or magnesium before feeding 4

Administer thiamine prior to starting glucose infusion to reduce risk of Wernicke's encephalopathy. 3

Context-Specific Laboratory Considerations

For Liver Disease Patients

• Use liver-specific nutritional screening tools like the Royal Free Hospital-nutritional prioritizing tool (RFH-NPT) 1
• CT scan at L3 vertebra to measure skeletal muscle index for sarcopenia assessment 4
• DEXA or bioelectrical impedance analysis if no fluid retention present 4
• Correct body weight for fluid retention by subtracting percentages based on ascites severity (mild 5%, moderate 10%, severe 15%) plus additional 5% if bilateral pedal edema 4

For Chronic Kidney Disease Patients

• Monitor body weight and serum albumin every 3 months in patients with GFR <30 ml/min per 1.73 m² 1
• Evaluate for causes and provide dietary counseling if body weight decreases unintentionally by >5% or serum albumin decreases by >0.3 g/dL 1

Common Clinical Pitfalls to Avoid

• Never rely solely on albumin as a malnutrition marker without inflammatory markers 1
• Do not interpret weight changes without assessing fluid status, as edema and ascites make weight measurements unreliable 1
• Avoid using transferrin alone as it shows poor correlation with nutritional status in many populations 1
• Do not delay nutritional intervention to obtain extensive micronutrient panels in acutely ill patients; basic metabolic assessment is sufficient to start safely 3