Nutritional Assessment

Lecture Objectives

  • Highlight different nutritional screening and assessment tools

  • Calculate ideal body weight (IBW), adjusted body weight (AdjBW), body mass index (BMI), body surface area (BSA), and daily caloric needs using the Harris Benedict equation

  • Analyze laboratory data in the context of nutritional status

  • Understand drug-nutrient interactions and their clinical significance

Nutrition Screening

  • To identify risk factors of malnutrition

  • Encompasses undernutrition and overnutrition (obesity)

  • Undernutrition

    • Unintended weight loss

    • Chronic disease (COPD, RA)

    • Medications (roflumilast)

    • Malabsorptive states

    • Socioeconomic barriers

  • Overnutrition

    • PMH (PCOS, Cushings)

    • Family history of obesity

    • Medications (corticosteroids)

    • Poor dietary habits

    • Sedentary lifestyle

Tools to Assess Nutrition

  • WHO Growth Chart

    • Pediatric patients 0-24 months

    • Describes how children should grow given optimal living conditions

  • CDC Growth Chart

    • Patients 2-20 years

    • Describes typical growth pattern of US children from 1963-1994

  • Nutrition Focused Physical Exam (NFPE)

    • Assess physical findings of malnutrition

    • Muscle wasting, obesity, pallor, alopecia, ascites, jaundice

  • Anthropometric Measures

    • Weight, height, stature, head circumference, waist circumference

  • Anthropometrics

    • Total Body Weight (TBW)

      • Weight on the scale

      • Affected by fluid status

      • Used for most drug dosing

    • Ideal Body Weight (IBW)

      • Males: 50 kg + 2.3 (height over 60 inches)

      • Females: 45.5 kg + 2.3 (height over 60 inches)

    • Adjusted Body Weight (AdjBW) = IBW + 0.4(TBW - IBW)

Body Mass Index (BMI)

  • Weight (kg) / height (m²)

Body Surface Area (BSA)

  • BSA = (weight(kg⁡)⋅height(cm⁡)3600\sqrt{\frac{\left(weight\right.\left(\operatorname{kg}\right)\cdot height\left(\operatorname{cm}\right)}{3600}}

  • Often used for chemo dosing or specialized pediatric drug calculations

Laboratory Parameters

  • Albumin

    • 3.5-5.0 g/dL

    • Maintains plasma oncotic pressure

    • Less sensitive to acute changes

    • Insensitive marker of protein malnutrition (can indicate chronic malnutrition)

    • Low albumin → Correct levels of highly protein bound drugs (phenytoin) and Ca2+

  • Transthyretin (Prealbumin)

    • 15-36 mg/dL

    • Binds to thyroxine (T3 + T4)

    • More sensitive marker for acute changes

  • C-Reactive Protein (CRP)

    • < 1.0 mg/dL

    • Marker of inflammation, infection, trauma

  • Blood Urea Nitrogen (BUN)

    • 7-20 mg/dL

    • Reflects protein intake and kidney function

    • Elevated levels → Dehydration (20:1 ratio), renal impairment, or excessive protein intake

    • Low levels → Overhydration or liver disease

    • 1 g Nitrogen per 6.25 g protein

  • Transferrin

    • 200-400 mg/dL

    • Levels decrease in presence of inflammation or critical illness

    • Transport protein for iron

    • Indicator or protein status or iron deficiency

  • Serum Creatinine

    • 0.6-1.2 mg/dL

    • Reflects kidney function and muscle mass

    • Elevated levels → Renal impairment

    • Low levels → Reduced muscle mass or severe malnutrition

Nutrition Requirements

  • Indirect calorimetry is most accurate bedside method to determine energy requirements

Harris-Benedict Equation

  • Used to estimate energy requirements in adults

  • Incorporates age, height, weight sex

  • Estimates basal energy expenditure (BEE) in kcal/day

  • Males: BEE = 66 + (13.75 x weight (kg) + 5 x height (cm)) - 6.8 x age

  • Females: BEE = 655 + (9.6 x weight (kg) + 1.8 x height (cm)) - 4.7 x age

Drug-Nutrient Interactions

  • Zinc deficiency

    • ACEi/ARBs, thiazides, valproic acid

    • Hair loss, impaired immune function, delayed wound healing, taste changes

  • Vitamin D deficiency

    • Phenytoin, phenobarbital, corticosteroids, cholestyramine, colestipol, efavirenz

    • Osteoporosis, increased risk of fractures, rickets (children), bone pain

  • Vitamin B12 deficiency

    • PPIs, metformin, H2RAs

    • Cognitive disturbances, fatigue, memory loss, neuropathy, weakness, anemia