Iron-Binding Capacity , Transferrin, and Iron Saturation

(redirected from Fe Sat)

Iron-Binding Capacity (Total), Transferrin, and Iron Saturation

Synonym/acronym: TIBC, Fe Sat.

Common use

To monitor iron replacement therapy and assess blood iron levels to assist in diagnosing types of anemia such as iron deficiency.

Specimen

Serum (1 mL) collected in a gold-, red-, or red/gray-top tube.

Normal findings

(Method: Spectrophotometry for TIBC and nephelometry for transferrin)
TestConventional UnitsSI Units
(Conventional Units × 0.179)
TIBC250–350 mcg/dL45–63 micromol/L
(Conventional Units × 0.01)
Transferrin215–380 mg/dL2.15–3.8 g/L
Iron saturation20–50%
TIBC = total iron-binding capacity.

Description

Iron plays a principal role in erythropoiesis, the formation and maturation of red blood cells (RBCs), and is required for hemoglobin (Hgb) synthesis.The human body contains between 4 and 5 grams of iron, about 65% of which is present in hemoglobin and 3% of which is present in myoglobin, the oxygen storage protein found in skeletal and cardiac muscle. A small amount is also found in cellular enzymes that catalyze the oxidation and reduction of iron. Excess iron is stored in the liver and spleen as ferritin and hemosiderin. Any iron present in the serum is in transit between the alimentary tract, the bone marrow, and available iron storage forms. Sixty to seventy percent of the body’s iron is carried by its specific transport protein, transferrin. For this reason, total iron-binding capacity (TIBC) and transferrin are sometimes referred to interchangeably, even though other proteins carry iron and contribute to the TIBC. Unbound iron is highly toxic, but there is generally an excess of transferrin available to prevent the buildup of unbound iron in the circulation. The percentage of iron saturation is calculated by dividing the serum iron value by the TIBC value and multiplying by 100.

This procedure is contraindicated for

    N/A

Indications

  • Assist in the diagnosis of iron-deficiency anemia
  • Differentiate between iron-deficiency anemia and anemia secondary to chronic disease
  • Monitor hematological response to therapy during pregnancy and iron-deficiency anemias
  • Provide support for diagnosis of hemochromatosis or diseases of iron metabolism and storage

Potential diagnosis

Increased in

  • Acute liver disease
  • Hypochromic (iron-deficiency) anemias (insufficient circulating iron levels to saturate binding sites)
  • Late pregnancy

Decreased in

    Chronic infections (transferrin is a negative acute-phase reactant protein and during periods of inflammation will demonstrate decreased levels) Cirrhosis (transferrin is a negative acute-phase reactant protein and during periods of inflammation will demonstrate decreased levels) Hemochromatosis (occurs early in the disease as intestinal absorption of iron available for binding increases) Hemolytic anemias (transferrin becomes saturated, and the iron-binding capacity is significantly decreased) Neoplastic diseases (transferrin is a negative acute-phase reactant protein and during periods of inflammation will demonstrate decreased levels) Protein depletion (transferrin contributes to the total protein concentration and will reflect a decrease in protein depletion) Renal disease (transferrin is a negative acute-phase reactant protein and during periods of inflammation will demonstrate decreased levels) Sideroblastic anemias (transferrin becomes saturated, and the iron-binding capacity is significantly decreased) Thalassemia (transferrin becomes saturated, and the iron-binding capacity is significantly decreased)

Critical findings

    N/A

Interfering factors

  • Drugs that may increase TIBC levels include mestranol and oral contraceptives.
  • Drugs that may decrease TIBC levels include asparaginase, chloramphenicol, corticotropin, cortisone, and testosterone.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in diagnosing anemia.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s hematopoietic system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include biopsy bone marrow, biopsy liver, CBC, CBC RBC count, CBC RBC indices, CBC RBC morphology, CBC WBC count and differential, erythropoietin, ferritin, folate, FEP, gallium scan, hemosiderin, lead, porphyrins, reticulocyte count, and vitamin B12.
  • Refer to the Hematopoietic System table at the end of the book for related tests by body system.