Iron deficiency anemia laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.D. [2]

Overview

Iron status can be assessed through several laboratory tests. Since, each test assesses a different aspect of iron metabolism, results of one test may not always agree with results of other tests. Hematological tests based on characteristics of red blood cells (i.e., Hb concentration, hematocrit, mean cell volume, and red blood cell distribution width) are generally more available and less expensive than are biochemical tests. Biochemical tests (i.e., erythrocyte protoporphyrin concentration, serum ferritin concentration, and transferrin saturation), however, detect earlier changes in iron status. Except for Total iron binding capacity TIBC, transferrin saturation, and soluble transferrin receptor all other components of iron study are decreased in iron deficiency anemia. The soluble transferrin receptor test is a newer test and is found useful in distinguishing iron deficiency anemia from anemia of chronic disease.

Laboratory Findings

Iron studies

• Iron studies should be done in patients with microcytic anemia to confirm the diagnosis of iron deficiency anemia. The tests usually done for iron deficiency anemia are:
  • Serum iron- Decreased in iron deficiency
  • Transferrin- Elevated in iron deficiency
  • Total iron binding capacity (TIBC)- Elevated in iron deficiency.
  • Transferrin saturation- derived by dividing the serum iron by the TIBC. Decreased in iron deficiency.
  • Ferritin- Indicator of body iron stores and is low in iron deficiency. However, ferritin also acts as an acute phase reactant and can be unreliable in inflammatory illness.

Change in lab values in iron deficiency anemia

Change	Parameter
Decrease	ferritin, hemoglobin, MCV
Increase	TIBC, transferrin, RDW

General facts

• Although all of these tests can be used to assess iron status, no single test is accepted for diagnosing iron deficiency.
• Lack of standardization among the tests and a paucity of laboratory proficiency testing limit comparison of results between laboratories.
• Laboratory proficiency testing is currently available for measuring Hb concentration, hematocrit, red blood cell count, serum ferritin concentration, and serum iron concentration, total iron-binding capacity, erthrocyte protoporphryin concentration.
• Regardless of whether test standardization and proficiency testing become routine, better understanding among health-care providers about the strengths and limitations of each test is necessary to improve screening for and diagnosis of iron-deficiency anemia, especially because the results from all of these tests can be affected by factors other than iron status.
• Because of their low cost and the ease and rapidity in performing them, the tests most commonly used to screen for iron deficiency are Hb concentration and Hct).
• These measures reflect the amount of functional iron in the body.
• The concentration of the iron-containing protein Hb in circulating red blood cells is the more direct and sensitive measure.
• Hct indicates the proportion of whole blood occupied by the red blood cells; it falls only after the Hb concentration falls.
• Since, changes in Hb concentration and Hct occur only at the late stages of iron deficiency, both tests are late indicators of iron deficiency.
• Anemia will be diagnosed on the basis of suggestive symptoms, or found on the basis of routine testing, which includes a complete blood count (CBC).
• A sufficiently low hemoglobin or hematocrit value is diagnostic of anemia, and further studies will be undertaken to determine its cause.
• One of the first abnormal values to be noted on a CBC will be a high red blood cell distribution width (RDW), reflecting a varied size distribution of red blood cells.
• The diagnosis of iron deficiency anemia will be suggested by appropriate history (e.g., anemia in a menstruating woman), and by such diagnostic tests as a low serum ferritin, a low serum iron level, an elevated serum transferrin and a high total iron binding capacity (TIBC). Serum ferritin is the most sensitive lab test for iron deficiency anemia.

• It is possible that the fecal occult blood test might be positive, if iron deficiency is the result of gastrointestinal bleeding.
• Laboratory values have to be interpreted with the lab's reference values in mind and considering all aspects of the individual clinical situation.
• Serum ferritin can be elevated in inflammatory conditions and so a normal serum ferritin may not always exclude iron deficiency.