Body Composition, Laboratories, and Other Studies | |
| TEST | NOTES |
|---|---|
| Body composition studies | |
| Anthropometrics | Skinfolds and circumferences require training for reliability. Typical coefficient of variation is ≥10%. |
| Bioelectrical impedance | Based upon differential resistance of body tissues. Equipment easily portable. Good measure of body water. Requires population-specific validation of regression equations. |
| Water displacement | Impractical for most clinical settings. Weighed in water tank. Historic reference measure. |
| Whole body counting and isotope dilution techniques | Research methodologies. Naturally occurring 40 K isotope to measure body cell mass by whole body counting. Total body water measurement by dilution volume of tritium, deuterium, or 18 O-labeled water. |
| Air plethysmography | Research methodology. Subject sits inside moderately sized BodPod chamber. Validated against water displacement and impedance. |
| Dual energy x-ray absorptiometry (DEXA) | Often used for bone density but can be used for soft tissue measurements with appropriate software. Can compare truncal and appendicular components. Modest x-ray exposure. |
| Imaging with computed tomography (CT) or magnetic resonance imaging (MRI) | State-of-the-art research methods for visualizing body tissue compartments. Can quantify visceral fat. Costly and CT entails x-ray exposure. |
| Laboratories and other studies | |
| Albumin | Lacks sensitivity and specificity for malnutrition. Potent risk indicator for morbidity and mortality. Proxy measure for underlying injury, disease, or inflammation. Half-life is 14-20 days. Also consider liver disease, nephrotic syndrome, and protein-wasting enteropathy. |
| Prealbumin | Sensitive to short-term changes in inflammation and protein nutrition with half-life of 2-3 days. Otherwise suffers the same limitations of albumin with limited sensitivity and specificity for malnutrition. Levels may be decreased in liver failure and increased in renal failure. |
| Transferrin | Acute phase reactant also altered by perturbation in iron status. Half-life is 8-10 days. Lacks sensitivity and specificity for malnutrition. |
| Retinol-binding protein | Responds to very short-term changes in nutritional status but utility is also limited by response to stress and inflammation. Half-life is 12 h. Also affected by vitamin A deficiency and renal disease. |
| C-reactive protein | C-reactive protein is a positive acute phase reactant. It is generally elevated if an active inflammatory process is manifest. |
| Cholesterol | Low cholesterol (<160 mg/dL) is often observed in malnourished persons with serious underlying disease. It is unrelated to dietary intake in many clinical settings. Increased complications and mortality are observed. It appears that low cholesterol is again a nonspecific feature of poor health status that reflects cytokine-mediated inflammatory condition. Vegans and pts with hyperthyroidism may also exhibit low cholesterol. |
| Carotene | Nonspecific indicator of malabsorption and poor nutritional intake. |
| Cytokines | Research is exploring prognostic use of cytokine measurements as indicators of inflammatory status. |
| Electrolytes, blood urea nitrogen (BUN), creatinine, and glucose | Monitor for abnormalities consistent with under- or over-hydration status and purging (contraction alkalosis). BUN may also be low in the setting of markedly reduced body cell mass. BUN and creatinine are elevated in renal failure. Hyperglycemia may be nonspecific indicator of inflammatory response. |
| Complete blood count with differential | Screen for nutritional anemias (iron, B12, and folate), lymphopenia (malnutrition) and thrombocytopenia (vitamin C and folate). Leukocytosis may be observed with inflammatory response. |
| Total lymphocyte count | Relative lymphopenia (total lymphocyte count <1200/mm3 ) is a nonspecific marker for malnutrition. |
| Helper/suppressor T cell ratio | Ratio may be reduced in severely undernourished pts. Not specific for nutritional status. |
| Nitrogen balance | 24-h urine can be analyzed for urine urea nitrogen (UUN) to determine nitrogen balance and give indication of degree of catabolism and adequacy of protein replacement. Requires accurate urine collection and normal renal function. Nitrogen balance = (protein/6.25) - (UUN + 4). Generally negative in the setting of acute severe inflammatory response. |
| Urine 3-methylhistidine | Indicator of muscle catabolism and protein sufficiency. Released upon breakdown of myofibrillar protein and excreted without reutilization. Urine measurement requires a meat-free diet for 3 days prior to collection. |
| Creatinine height index (CHI) | CHI = (24-h urinary creatinine excretion/ideal urinary creatinine for gender and height) × 100. Indicator of muscle depletion. Requires accurate urine collection and normal renal function. |
| Prothrombin time/international normalized ratio (INR) | Nonspecific indicator of vitamin K status. Prolonged in liver failure. |
| Specific micronutrients | When suspected a variety of specific micronutrient levels may be measured: thiamine, riboflavin, niacin, folate, pyridoxine, vitamins A, C, D, E, B12, zinc, iron, selenium, carnitine, and homocysteine-indicator of B12, folate, and pyridoxine status. |
| Skin testing-recall antigens | Delayed hypersensitivity testing. While malnourished pts are often anergic, this is not specific for nutritional status. |
| Electrocardiogram | Severely malnourished pts with reduced body cell mass may exhibit low voltage and prolonged QT interval. These findings are not specific for malnutrition. |
| Video fluoroscopy | Helpful to evaluate suspected swallowing disorders. |
| Endoscopic and x-ray studies of gastrointestinal tract | Useful to evaluate impaired function, motility, and obstruction. |
| Fat absorption | 72-h fecal fat can be used to quantitate degree of malabsorption. |
| Schilling test | Identify the cause for impaired vitamin B12 absorption. |
| Indirect calorimetry | Metabolic cart can be used to determine resting energy expenditure (REE) for accurate estimation of energy needs. Elevated REE is a sign of systemic inflammatory response. |