What laboratory bloodwork parameters reflect malnutrition?

Laboratory Bloodwork Reflecting Malnutrition

The core laboratory panel for assessing malnutrition should include serum albumin, prealbumin (transthyretin), complete blood count with hemoglobin and total lymphocyte count, comprehensive metabolic panel with electrolytes, and lipid profile including total cholesterol and triglycerides. 1, 2

Essential Core Laboratory Tests

Protein Markers

• Prealbumin (transthyretin) is the preferred marker over albumin due to its shorter half-life (2-3 days vs 20 days), making it more responsive to acute nutritional changes and better for monitoring nutritional interventions 1, 3
• Serum albumin should be measured every 3 months in at-risk patients, but critically, it must always be interpreted alongside inflammatory markers (C-reactive protein) because albumin is a negative acute phase reactant that drops during inflammation regardless of nutritional status 1, 2, 3, 4
• A decrease in serum albumin >0.3 g/dL or levels <4.0 g/dL (Bromo-Cresol-Green assay) or <3.7 g/dL (Bromo-Cresol-Purple assay) warrants evaluation for malnutrition 1
• Total protein levels correlate with malnutrition risk and should be included in the assessment 5, 6

Hematologic Parameters

• Hemoglobin levels are consistently lower in malnourished patients and serve as a reliable biomarker across clinical settings 2, 5, 6
• Total lymphocyte count reflects immune function and protein status, with lower counts indicating more severe malnutrition 1, 2, 4
• Complete blood count helps assess for anemia and immune dysfunction associated with malnutrition 2, 3

Lipid Profile

• Total cholesterol is significantly lower in malnourished patients and represents a useful biomarker that is less affected by acute inflammation compared to protein markers 5, 6
• Triglycerides should be monitored, as they may be elevated or low depending on malnutrition type 1, 3, 4
• LDL and HDL cholesterol show significant differences between malnourished and well-nourished patients 6

Electrolytes and Metabolic Panel

• Routine electrolytes (sodium, potassium, calcium, phosphorus, magnesium) must be checked to identify nutritional deficiencies and prevent refeeding syndrome 1, 3, 4
• Serum urea helps determine protein requirements and may be elevated in severe malnutrition due to increased protein catabolism 1, 3
• Creatinine may be falsely low in malnourished patients due to reduced muscle mass 3

Micronutrient Assessment

Initial Micronutrient Panel

• Vitamin B12 and folate levels should be checked to identify deficiencies causing megaloblastic anemia and neurological complications 2
• Vitamin D levels should be assessed, with sufficient levels considered ≥75 nmol/L 2
• Iron studies (serum ferritin and transferrin saturation) are essential for evaluating iron status and anemia 2

Extended Micronutrient Testing (When Indicated)

• Thiamine (B1) is critical if rapid weight loss, poor dietary intake, vomiting, alcohol abuse, or neurological symptoms are present, and should be administered before glucose infusion to prevent Wernicke's encephalopathy 2, 4
• Zinc and copper levels should be checked with unexplained anemia, hair loss, poor wound healing, or taste changes 2
• Selenium levels are indicated with chronic diarrhea, metabolic bone disease, unexplained anemia, or cardiomyopathy 2
• Vitamin A assessment is warranted with night blindness, xerophthalmia, or protein malnutrition 2
• Vitamins E and K should be checked in malabsorption or unexplained neuropathy 2

Long-Term Monitoring

• For patients on long-term parenteral nutrition, measure trace elements and vitamins A, E, D, B12, and folic acid at 12-month intervals 2

Inflammatory Markers (Critical for Interpretation)

• C-reactive protein (CRP) must be measured alongside albumin and prealbumin to correctly interpret their values—elevated CRP indicates inflammation, which causes these proteins to drop regardless of nutritional status 1, 2, 3, 4
• Orosomucoids and other inflammatory proteins should be considered when interpreting albumin levels 1

Monitoring Frequency Algorithm

Severe Malnutrition or High-Risk Patients

• Daily monitoring is required for critically ill patients, newborns/infants, those at refeeding syndrome risk, or patients transitioning between feeding routes 1, 3
• Glucose should be measured initially and at least every 4 hours for the first two days when starting artificial nutrition 1
• Electrolytes (potassium, magnesium, phosphate) should be measured at least once daily for the first week 1

Stable Patients

• Every 3 months for patients with GFR <30 mL/min per 1.73 m² or chronic malnutrition: measure body weight and serum albumin at minimum 1, 2
• 2-3 times per week for clinically stable hospitalized patients 1, 3
• At least annually for stable outpatients 2

Critical Pitfalls to Avoid

• Never rely solely on albumin as a malnutrition marker in hospitalized or acutely ill patients—it is more accurately a marker of disease severity and inflammation rather than nutritional status 1, 3, 4
• Do not interpret albumin or prealbumin without assessing inflammatory status (CRP)—both are negative acute phase reactants that decrease during inflammation regardless of nutritional intake 1, 3, 4
• Edema and ascites can mask weight loss and muscle wasting, making weight measurements unreliable; assess fluid status alongside weight 1, 3
• Do not delay nutritional intervention waiting for laboratory confirmation if clinical signs of malnutrition are present 3
• BMI alone should not be used as it does not correlate well with postoperative complication risk 3
• In patients with acute illness, trauma, or significant inflammation, albumin and prealbumin will decrease regardless of nutritional status and should not guide diagnosis 3, 5

Clinical Action Thresholds

• Unintentional weight loss >5% or serum albumin decrease >0.3 g/dL requires evaluation for causes and dietary counseling 1
• Each 1 g/dL decrease in serum albumin increases malnutrition risk 5.21 times 6
• Insufficient food intake ≤50% of energy requirements over 3 days should trigger nutritional intervention 3