Nutritional Assessment: Biochemical Methods

Biochemical Assessment

• Used to detect subclinical deficiency states and supplement other assessment methods
• Two methods to identify subclinical deficiency:
• Biochemical tests: measuring nutrients and their metabolites
• Functional tests: measuring production of abnormal metabolite or change of enzyme activity dependent on a certain nutrient or physiological or behavioral functions dependent on a specific nutrient

Advantages of Biochemical Assessment

• Most objective and precise method among all other assessment methods
• Detects marginal subclinical deficiency before they result in overt signs
• Only method that can detect nutrient deficiency and supplement other methods of evaluation
• Measures the extent of functional consequences of a specific nutrient deficiency (functional vs biochemical)
• Useful to validate data obtained from dietary methods (e.g., comparing salt intake with 24-hour urinary excretion)
• Precise, accurate, and reproducible

Disadvantages of Biochemical Assessment

• Affected by technical and biological factors other than depleted body stores of the nutrient
• Limitation can be avoided by standardizing sampling and collection procedure
• May be altered due to organ function, disease states, hydration status, medications, and fasting or non-fasting

Specimen Types

• Blood (whole, serum, or plasma) reflects recent dietary intake (acute term index)
• Erythrocytes (red blood cells): reflects chronic status, unlikely to be a valid index for some nutrients
• Leukocytes (white blood cells): more sensitive than erythrocytes, but has technical difficulties
• Storage tissues: liver, bone marrow, adipose tissue, and bones

Clinical Chemistry Panels

• Basic Metabolic Panel (BMP) or Chem 7: measures sodium, potassium, chloride, CO2, glucose, blood urea nitrogen, and creatinine
• Comprehensive Metabolic Panel (CMP) or Chem 20: includes calcium, albumin, total protein, liver function tests, and above-mentioned tests
• Complete Blood Count (CBC): includes red blood cells, hemoglobin, hematocrit, mean corpuscular volume, white blood cell count, and differential

Protein-Energy Malnutrition (PEM)

• Kwashiorkor: visceral proteins are depleted with advanced stages due to inadequate intake of protein and/or hypermetabolic state
  • Signs and symptoms: edema, muscle wasting, psychomotor changes, anemia, and growth retardation
• Marasmus: represents the end result of starvation where both proteins and calories are deficient
  • Signs and symptoms: severe wasting of muscle and fats, growth retardation, child looks older than their age, no edema or hair changes, diarrhea, and dehydration

Acute-Phase Proteins

• Change by 25% during an acute-phase response
• Examples of negative acute-phase respondents: albumin, transthyretin or prealbumin, transferrin, retinol-binding protein (decrease)
• Examples of positive acute-phase reactants: C-reactive protein and fibrinogen (increase)

Assessment of PEM

• Biochemical tests provide the most objective and quantitative assessment for PEM
• Assessment includes:
  1. Hormonal and cell-mediated response to stress
  2. Nitrogen balance
  3. Hepatic transport proteins (albumin, transferrin, prealbumin, retinol-binding protein, and creatinine)
  4. Immunocompetence (e.g., C-reactive protein)