A child with a poor nutritional status and weight loss is at risk for a negative nitrogen balance. To help diagnose this problem, the nurse in charge anticipates that the doctor will order which laboratory test?
A. Total iron-binding capacity
B. Hemoglobin
C. Total protein
D. Serum transferrin
Correct Answer: C. Total protein
A negative nitrogen balance may result from inadequate protein intake and is best detected by measuring the total protein level. An increase in the protein intake produces an increase in nitrogen losses via higher amino acid oxidation, especially in the fed state, and a trend toward positivation of the nitrogen balance. Nitrogen balance and nitrogen levels at four levels of nitrogen intake in healthy adult subjects (data from Price et al. 1994).
Option A: TIBC (total iron-binding capacity)—measures the total amount of iron that can be bound by proteins in the blood. Since transferrin is the primary iron-binding protein, the TIBC test is a good indirect measurement of transferrin availability—the amount of transferrin that is available to bind to iron.
Option B: Hemoglobin (Hb) is the protein contained in red blood cells that is responsible for the delivery of oxygen to the tissues. To ensure adequate tissue oxygenation, a sufficient hemoglobin level must be maintained. When the hemoglobin level is low, the patient has anemia. An erythrocytosis is the consequence of too many red cells; this results in hemoglobin levels above normal.
Option D: Measuring serum transferrin levels would help detect iron-deficiency anemia, not a negative nitrogen balance. Transferrin can be used to assess the iron level in the body along with other markers in the body. Transferrin level testing is used to determine the cause of anemia, examine iron metabolism and determine the iron-carrying capacity of the blood.