Laboratory Indices of Nutritional Status

Laboratory values can be useful in assessing nutritional status or identifying those at high risk that may require nutrition intervention. However, caution is necessary when interpreting laboratory values, and results from single laboratory values should be interpreted carefully. The laboratory tests listed below are commonly used to evaluate either a direct or indirect relationship to a patient’s nutritional status. The negative acute-phase hepatic proteins albumin, pre-albumin, transferrin and retinol-binding protein are now considered better indicators of inflammatory metabolism, morbidity, mortality and severity of illness than nutritional status (1-4). These proteins can decrease by as much as 25% as a result of inflammatory metabolism caused by acute or chronic disease (1). In addition, these proteins are not directly linked to nutrition deprivation as once thought (1-4). Because of their ability to predict severity of illness, they can be used to indirectly identify the sickest patients who most likely will require nutritional interventions and medical nutrition therapy (1,2,4). It has currently been suggested that diagnostic classifications of malnutrition be revised to accommodate the interface between uncomplicated malnutrition and that associated with disease and trauma (1).

Test	Purpose/Definition	Normal Range	Discussion
Protein Status
Albumin	Indicator of inflammatory metabolism, morbidity, mortality, or severity of illness (1-4)	3.5 – 5.0 g/dL	Should not be used as an indicator of nutritional status Use as an indicator of inflammatory metabolism, morbidity, mortality, or severity of illness (1-4) Elevated levels occur in dehydration. Low in uncomplicated malnutrition (without existing acute or chronic disease) (1)
Pre-albumin	Indicator of inflammatory metabolism, morbidity, mortality, or severity of illness (1-4)	19 – 43 mg/dL	Should not be used as an indicator of nutritional status Use as an indicator of inflammatory metabolism, morbidity, mortality, or severity of illness (1-4) More sensitive to dietary change than albumin post fasting, (4,5). Low in uncomplicated malnutrition (without existing acute or chronic disease) (1)
Protein, total	Total protein is of little value as a sensitive index for estimating protein nutritional status	Serum value 6.4 – 8.3 g/dL	Decreased values occur with: nephrosis severe burns malnutrition overhydration hepatic insufficiency Increased values occur with: multiple myeloma dehydration
Transferrin	Indicator of inflammatory metabolism, morbidity, mortality, or severity of illness (1-4)	200 – 400 mg/dL	Should not be used as an indicator of nutritional status Use as an indicator of inflammatory metabolism, morbidity, mortality, or severity of illness (1-4) Decreases with anemia and protein-energy malnutrition (uncomplicated by acute or chronic disease) Increases with iron deficiency, infection, oral contraceptives, and pregnancy
Urea nitrogen	Urea is the principal end product of protein catabolism	10 – 20 mg/dL Values may be slightly higher in the elderly	Decreased values occur with: liver impairment decreased protein intake overhydration malabsorption high-carbohydrate, low-protein diets Increased values occur with: renal insufficiency GI bleeding dehydration lower urinary tract infection diabetes mellitus obstruction starvation congestive heart failure excessive protein intake or protein catabolism
Hematologic Status
Red blood cells (RBCs)	Measures the number of RBCs in whole blood	M: 4.5 – 6.0 million/mm3 F: 4.0 – 5.5 million/mm3	Decreased values occur with: anemia chronic infection leukemia Increased values occur with: dehydration
Test	Purpose/Definition	Normal Range	Discussion
Hemoglobin (Hgb)	Part of the red blood cells that carries oxygen and carbon dioxide in the blood	M: 13 – 18 g/100 dL F: 12 – 16 g/100 dL	Men’s Hgb may drop 1 – 2 g/100 mL with age. Women have no documented change. Although Hgb declines with age, other signs should be reviewed, eg, pale skin, pale conjunctiva.
Hematocrit (HCT)	Measures the percent of RBCs in the total blood volume	M: 42% – 52% F: 37% – 47%	Values may decrease slightly in the elderly
Mean corpuscular hemoglobin concentration (MCHC)	Measures the concentration of Hgb per unit of red blood cells	32% – 36%	Values <30 indicate advanced iron deficiency anemia
Mean corpuscular volume (MCV)	Measures the average size of the RBC	80 – 95 mm3	Increased values indicate pernicious anemia. Decreased values indicate iron deficient anemia.
Ferritin	Provides an index of iron stores in iron deficiency and iron overload	M: 12 – 300 mg/L F: 10 – 150 mg/L	Significantly higher in mend and post menopausal women. Decreased values occur with iron or protein deletion. Increased values occur with iron excess.
Prothrombin time (PT)	Measures velocity of blood clotting and is an indirect measure of vitamin K status	Adults: 11 – 12.5 seconds 85% – 100% of control	Increased values occur with: vitamin K deficiency (common in elderly and hospitalized) liver disease fat malabsorption drug therapy (antibodies, anticoagulants, aspirin) PT >25 seconds is associated with major bleeding