Malnutrition refers to disorder of nutritional status from either a deficiency or excess (i.e. imbalance) of energy, protein, and/or other nutrients that lead to adverse effects on tissue and body form and function as well as adverse clinical outcomes.¹ Malnutrition therefore includes undernutrition, overweight, and obesity. Despite significant advances in prevention and treatment worldwide, malnutrition continues to have a substantial negative impact on child morbidity and mortality.² The prevalence of undernutrition among hospitalized children in the United States and other resource-rich countries may be as high as 50%, but it varies considerably by age and disease state.^3-6 The presence of undernutrition, overweight, and obesity among hospitalized children has also been associated with an increased risk of adverse clinical events, prolonged length of stay, and increased hospital charges and costs.^3-7 This chapter addresses undernutrition, focusing on problems relating to inpatient care. Chapter 23 addresses failure to thrive.

Pediatric undernutrition is defined as an imbalance between nutrient requirement and intake, resulting in cumulative deficits of energy, protein, or micronutrients that may negatively affect growth, development, and other outcomes.⁶ Undernutrition is often related to environmental or behavioral factors. However, many hospitalized children have illness-related malnutrition, with one or more conditions directly resulting in a nutrient imbalance. This occurs as a result of decreased nutrient intake, altered utilization, excessive nutrient losses, or increased nutrient requirements not matched by intake.⁶ Furthermore, illness-related malnutrition is often associated with an inflammatory component, which may increase nutrient requirements and promote a nutrient-wasting catabolic state. The presence and severity of the inflammatory state may also impair the effectiveness of therapeutic nutrition interventions. Secondary complications include compromised immune function, impairments of gastrointestinal (GI) tract function, suboptimal response to medical or surgical therapy, and abnormal cognitive and behavioral development.^3,6

Physical examination findings in children with malnutrition are variable and related to the chronicity, severity, and type of nutrient imbalance. Table 81-1 lists some of the findings associated with deficiencies of both macro- and micronutrients. Excessive intake of nutrients from overfeeding or unbalanced dietary intake can also result in abnormal physical examination findings, such as increased subcutaneous fat. Abnormal growth ultimately occurs in all patients with ongoing undernutrition, and in some cases it may be the only objective marker of poor nutritional status. Careful anthropometric measurements can assess growth cross-sectionally (e.g. triceps skinfold thickness) or longitudinally (length or height).

Historically, physical findings and anthropometry have been used to divide patients with malnutrition into two broad categories: marasmus and kwashiorkor.⁸ Marasmus develops after chronic and severe calorie deprivation, resulting in weight loss and marked wasting of fat and muscle stores. Because visceral protein stores are generally preserved, edema does not develop. Although both height and weight measurements are abnormally low, weight is often decreased out of proportion to height. Kwashiorkor develops in acute or chronic situations when protein deficits exceed caloric deficits. Decreased visceral protein stores result in muscle wasting, edema, and changes in the skin and hair. Although some degree of growth failure is likely, weight may appear normal for height due to fluid retention. More recently, the term protein–energy malnutrition has been used to describe states of malnutrition in which there are interrelated deficiencies in carbohydrates, proteins, and fat, as well as vitamins, minerals, and trace elements. As a consequence of these multinutrient imbalances, children may have a combination of physical signs.

Nutrition screening can identify individuals who are malnourished or at risk for malnutrition to determine whether a more detailed assessment of nutrition is indicated.³ Several formal screening tools have been studied and validated in hospitalized pediatric patients, and risk factors for malnutrition have been identified (Table 81-2).^5,6 The presence of one or more of these risk factors should prompt a comprehensive evaluation using the history, physical examination, anthropometric measurements, and laboratory data to define nutritional status and develop a proper nutrition care plan.

The medical history should include use of any dietary supplements, a careful recall diet history, and a detailed psychosocial history. Special emphasis should be placed on conditions or medications that impair the ability to ingest and absorb food or that might result in high metabolic demands. The dietary history should focus on the type and preparation of food or formula, the amount and frequency of feedings, and the route of feeding. Prospectively, a 3- to 5-day diet diary can provide an objective and accurate method of assessing dietary intake in the home setting and may be an important part of discharge recommendations. Important psychosocial factors include adequacy of resources to purchase, store, and prepare food; level of parental knowledge and skills; drug and alcohol use or mental illness among caregivers; and potential child abuse or neglect.

A thorough physical examination and precise anthropometric measurements provide convenient and noninvasive methods for evaluating both acute and chronic nutritional status. Basic measurements include weight, height (for children aged 2 years or older) or recumbent length (for those younger than 2 years), and head circumference (children younger than 2 years). Body mass index (BMI) is the best measure of adiposity and is commonly used to define underweight, overweight, and obesity in children older than 2 years. It is calculated by the following formula:

The use of published charts as reference standards for growth varies by the age and condition of the child. For children up to 2 years of age who are measured in the supine position for length, use of the 2006 World Health Organization (WHO) charts is recommended.⁹ For children and adolescents aged 2 to 20 years who are measured with a standing height, the 2000 Centers for Disease Control and Prevention charts are recommended.¹⁰ Reference values for children with special health care needs are also available. Experts recommend using z scores, which express in standard deviation units how far a child’s measurements are from the mean of the population reference standard.⁶

The weight-for-height value is the ratio of the patient’s actual weight to the ideal weight for the patient’s height. When acute medical conditions result in short-term nutritional deprivation, the body weight is depleted out of proportion to height (or length), and the weight-for-height value is low. Conversely, chronic malnutrition affects both weight gain and linear growth, resulting in a small child with a body weight that is more proportional to height (or length). The Waterlow criteria use the weight-for-height value and a similar measure, the height-for-age value, to differentiate and classify acute and chronic malnutrition (Table 81-3).¹¹ Chronic malnutrition is often characterized by a height-for-age that is less than –2 z scores.⁶

Although there is no single laboratory test and no standard panel of tests for malnutrition, several common blood tests can provide important information about nutritional status. The initial evaluation usually includes the following:

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  Complete blood count, with red blood cell indices, white blood cell differential, and peripheral smear

  
  
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  Liver enzymes, including albumin and prothrombin time, and bilirubin

  
  
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  Electrolytes (including calcium, phosphorus, and magnesium)

  
  
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  Prealbumin

  
  
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  C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR)

Further testing may be indicated based on abnormalities identified through the initial evaluation. Depletion of electrolyte stores or metabolic bone disease may result in abnormal chemistry and mineral profiles. A number of vitamin and mineral deficiencies can result in lymphopenia and thrombocytopenia, as well as hemolytic, microcytic, or megaloblastic anemia. Vitamin K deficiency often leads to a prolonged prothrombin time. CRP and ESR can indicate the degree of concomitant inflammation.

Serum protein levels often reflect the degree of malnutrition, but they must be interpreted with caution because they can be influenced by the presence of systemic disease as well as the body’s response to trauma, infection, and inflammation.¹² Because albumin has a half-life of 14 to 20 days and undergoes shifts in body stores with changes in acute nutritional status, it is a more reflective indication of chronic malnutrition. Other proteins synthesized by the liver have shorter half-lives and more accurately reflect acute changes in protein stores and metabolism. These include transferrin (half-life 8 days), prealbumin (half-life approximately 2 days), and retinol-binding protein (half-life 12 hours).

If renal function is normal, urine studies can provide additional information about total-body protein reserves and turnover. The creatinine–height index evaluates lean muscle mass by comparing the patient’s 24-hour urinary creatinine excretion with the predicted urinary excretion for a child of similar height. Nitrogen balance compares 24-hour protein intake with 24-hour urinary urea nitrogen and reflects the rate of protein turnover. A positive nitrogen balance indicates an anabolic state, and a negative nitrogen balance indicates a catabolic state.