What laboratory tests are used to screen for nutritional disorders in patients?

Laboratory Tests for Nutritional Disorder Screening

The essential laboratory screening panel for nutritional disorders includes a complete blood count (CBC) and comprehensive metabolic panel (CMP) with electrolytes, liver enzymes, and renal function tests, as these provide the foundational assessment of nutritional status and metabolic derangements. 1

Core Laboratory Panel

Standard Initial Testing

• Complete Blood Count (CBC): Screens for anemia (iron, B12, folate deficiency), leukopenia (protein-energy malnutrition), and other hematologic abnormalities 1
• Comprehensive Metabolic Panel (CMP): Includes electrolytes (sodium, potassium, chloride, bicarbonate), glucose, calcium, liver enzymes (AST, ALT, alkaline phosphatase, bilirubin), and renal function tests (BUN, creatinine) 1
• Albumin and Prealbumin: While serum albumin is commonly measured, it is more a marker of disease severity and inflammation than pure nutritional status, as it is a negative acute phase reactant 1

Important Caveats About Albumin

The albumin concentration reflects synthesis, breakdown, volume of distribution, exchange between intra- and extravascular spaces, and losses—not just nutritional status 1. Albumin values should never be interpreted in isolation and must be combined with thorough physical examination and clinical judgment 1. During acute illness, albumin synthesis decreases, resulting in low serum levels independent of nutritional intake 1.

Additional Laboratory Tests Based on Clinical Context

Micronutrient Assessment

• Calcium, magnesium, and zinc levels may be important in specific clinical scenarios 1
• Laboratory measurement of micronutrient levels (vitamins, trace elements) may be appropriate in selected cases, particularly in patients with history of bariatric surgery, fatty liver disease, or chronic malabsorption 1
• Trace elements and vitamins should be measured at 12-month intervals in patients on long-term parenteral nutrition 2

Specialized Testing

• Electrocardiogram (ECG): Required in patients with restrictive eating disorders, severe purging behavior, or those taking medications that prolong QTc intervals 1
• Electrolyte monitoring: Critical care patients and those with severe malnutrition require daily monitoring of electrolytes and glucose during initial stabilization to prevent refeeding syndrome 2

Integration with Clinical Assessment

Laboratory tests alone are insufficient for nutritional screening and must be combined with validated screening tools, anthropometric measurements, and physical examination 1, 3, 2. The two-step approach recommended by ESPEN involves:

1. Rapid screening using validated tools (NRS-2002, MUST, MST) within 24-48 hours of admission 3, 2
2. Comprehensive assessment for at-risk patients, including laboratory evaluation as one component alongside medical history, physical examination, anthropometric measurements, body composition assessment, and functional testing 2, 4, 5

Body Composition Over Simple Anthropometry

Body composition assessment should be preferred to anthropometry measurements when diagnosing and monitoring malnutrition, particularly in hospitalized patients with kidney disease or critical illness 1. BMI and weight alone are poor nutritional assessment tools because they cannot distinguish fat from muscle stores or account for fluid overload 1.

Monitoring Frequency

• Daily monitoring: Critical care patients and those with severe malnutrition during initial stabilization 2
• Weekly monitoring: Hospitalized patients throughout their stay 6
• Every 3 months: Stable chronic malnutrition patients until stabilized 2
• Annual monitoring: Long-term parenteral nutrition patients for trace elements and vitamins 2

Common Pitfalls to Avoid

• Do not rely solely on albumin as a nutritional marker—it primarily reflects inflammation and disease severity 1
• Do not use laboratory values in isolation—they must be integrated with clinical assessment, screening tools, and physical examination 1, 2
• Do not delay screening—systematic screening should occur within 24-48 hours of first contact with healthcare services 3, 2
• Do not assume normal BMI excludes malnutrition—sarcopenic obesity and muscle wasting can occur despite normal or elevated BMI 1