Using albumin and prealbumin to assess nutritional status
Susan H. Smith, DNP, RN, ACNS-BC, replies: To better understand why the role of these lab values in the assessment of nutritional status has changed, first consider some basic physiology about proteins. Albumin is the most abundant plasma protein. Its essential role is to regulate passage of water and solutes through the capillaries by maintaining colloidal oncotic pressure within the vasculature.1 Plasma proteins have long been considered integral to assessment of nutritional status. During nutrient deprivation, protein synthesis by the liver is altered, resulting in low serum protein levels. Reduced protein levels are associated with poorer prognosis.2 Protein is an important macronutrient for healing wounds, supporting immune function and maintaining lean body mass.3
Prealbumin, also called transthyretin, is the precursor to albumin. Its half-life is 2 to 4 days, whereas the half-life of albumin is 20 to 22 days.4 Measuring prealbumin can help clinicians detect short-term impairment of energy intake and the effectiveness of nutritional support efforts.2
During acute illness, infection, and injury, a cytokine-mediated acute phase response occurs as a result of inflammation.5 Inflammation and illness increase vascular permeability, and hepatic protein synthesis is reprioritized.3 Synthesis of C-reactive protein, fibrinogen, calcitonin, and other proteins also occurs.5 As a result, albumin and prealbumin levels are reduced, not necessarily from poor nutrition but because of acute pathophysiologic events.6 Consequently, measuring serum albumin and prealbumin levels may not give clinicians an accurate picture of the patient's nutritional status.
Understanding a patient's nutritional status is very important. Nutritional imbalances result in malnutrition and contribute to morbidity, mortality, decreased function and quality of life, and higher healthcare costs.7 Some patients may enter the clinical setting with preexisting malnutrition, while others develop malnutrition during their illness. The prevalence of malnutrition in the hospital setting ranges from 20% to 50%.8
The risk of healthcare-acquired conditions such as injury from falls, infections, and pressure injuries can be minimized with improved patient nutrition. Nutrition interventions are low cost and effective with a high impact on patient outcomes.9
No single clinical or lab parameter can be used to determine the comprehensive nutritional status of a patient, particularly during an illness. Lab findings must be used in combination with other assessments to identify the patient's nutritional state.5 The diagnosis of malnutrition is made when two of the following six characteristics are identified:
Since 1996, The Joint Commission requires screening all patients for risk of malnutrition within 24 hours of admission to an acute care facility.9 The Academy of Nutrition and Dietetics also recommends screening patients to identify those who would benefit from a more in-depth nutritional assessment.7
Screening tools can help clinical nurses and other caregivers identify patients at greatest risk. Many have excellent sensitivity and specificity for identifying at-risk patients.9
Both the Society of Critical Care Medicine and American Society for Parenteral and Enteral Nutrition recommend the use of tools, such as the Nutritional Risk Screening (NRS) 2002 and the Nutrition Risk in Critically ill (NUTRIC) assessment tools, for critically ill patients. These tools account for nutrition status in relation to disease severity, which is important in this population.3 The NRS 2002 assesses body mass index, weight loss, dietary intake, and illness severity.10 The NUTRIC assessment includes age, APACHE II score, sepsis-related organ failure assessment (SOFA) score, patient comorbidities, ICU admission date, and interleukin-6 (IL-6, if available).