Nutrition Assessment

Body mass index (BMI) was introduced asa concept by Adolphe Quetelet in the 1830s in order to study average values of the population. However, the term “BMI” and its use as a health metric was popularized by Ancel Keys in 1972.

Primary Components

• History and physical exam
• History of weight loss, anorexia, and other indicators of poor nutritional intake
• Weight and BMI
• Serum albumin, Hb A1C, trace element levels (when relevant)
• Functional status
• Current disease state and physiologic status

Body Composition Assessment

• Noninvasive quantitative measures of body used to determine underlying nutritional status and diagnose obesity. These measurements can be compared to relative standards for the correct population.
• Elements
  • Height
  • Weight
  • BMI
    • Normal: 18.5-25
    • Severe malnutrition: <16
  • Head circumference (pediatric patients)
  • Body circumferences (assess for adiposity in waist, hip, and upper arm)
  • Skin fold thickness
• Tools for assessing
  • Dual-energy X-ray absorptiometry (DXA)
    • Evaluate metabolic bone disorders
    • Reliable for estimating body fat percentage
    • Limitations: weight limit of the scanning bed, width of scanning area, hydration differences in lean tissue
  • CT → L3 lumbar psoas used as landmark in cross-sectional body composition analysis as it corresponds to whole-body tissue measurements
  • MRI → estimate volume of total body fat as opposed to mass of subcutaneous adipose and visceral fat tissue

Biochemical Assessment

• Serum creatinine and nitrogen balance studies
  • Creatinine
    • Waste product of creatine (amino acid utilized in muscle to make energy)
    • Not bound to serum proteins, freely filtered by kidney glomerulus without tubular reabsorption → allows us to be able to use it to estimate GFR in normal renal function
  • Serum creatinine (SCr)  and creatinine height index (CHI) must be considered in full clinical picture to estimate nutrition status
    • SCr
      • Monitored as marker for renal function
      • Surrogate for measurement of muscle mass
      • Factors contributnig to low SCr
        • Malnutrition
        • Low protein (vegetarian) diet
        • Baseline low muscle mass (female sex, elderly)
        • Pregnancy
        • Fluid overload
        • Nephrotic syndromes
        • Advanced liver disease 
    • Creatinine height index (CHI)
      • Calculated using 24-hour urine creatinine to assess for degree of protein depletion
  • Nitrogen balance studies
    • Nitrogen intake – nitrogen loss = neg gain/loss of total body protein
    • Determined by
      • Urinary urea nitrogen excretion + 4 g/day (account for presumed losses through GI tract, integument, nonurea urinary loss, and insensible losses)
• Serum visceral protein
  • Characterized as negative acute-phase reactants, with their quality affected by many disease processes and drugs (especially those that alter liver function)
  • Examples
    • Albumin
      • Abundant serum hepatic protein
      • Functions in maintaining capillary oncot pressure and carrier for other molecules
      • Half-life: 20 days
    • Transthyretin (prealbumin)
      • Synthesized by liver
      • Functions as transport protein by binding to thyroxine and other small molecules
      • Half-life: 48-72 hours
      • Smaller total body pool than albumin → theoretically better indicator of nutritional status BUT
    • Transferrin
      • Serum transport protein for iron
      • Half-life: 8 days
    • Retinol-binding protein (RBP)
      • Low molecular weight protein
      • Functions to transport retinol from the liver to large organs
      • Half-life: 12 hours
      • Difficult to measure
  • In healthy patients, albumin and prealbumin don’t decrease until a ≥6 weeks of starvation.
  • Also unreliable because these numbers decrease with sepsis, trauma, cancer, burns, and postsurgery states. Additionally, prealbumin and transferrin are degraded by the kidneys, so they may be falsely elevated in those with any degree of renal dysfunction.
  • ASPEN (2021) → serum albumin and prealbumin aren’t components of currently accepted definitions of malnutrition and don’t serve as valid proxy measures of total body protein or total body mass.

Nutrition Assessment Tools

• Subjective Global Assessment (SGA)
• Birmingham Nutrition Risk Score
• Mini Nutritional Assessment (MNA)
• Malnutrition Universal Screening Tool (MUST)
• Elderly Nutritional Indicators for Geriatric Malnutrition Assessment (ENIGMA)
• Nutrition Risk Screening 2002 (NRS-2002) → used in critically ill inpatient population
• Nutrition Risk in the Critically Ill (NUTRIC) Score
• Perioperative nutrition screen (PONS)
  • Proposed as modified version of MUST
  • Based on BMI, recent weight changes, reported decrease in dietary intake, and preoperative albumin level

Nutrition Things to Remember

• Most important factor in assessing nutrition risk if recent unintentional weight loss (= >5% loss over preceding month or >10% loss over the preceding6 months)