Lab values in Iron Deficiency Anemia

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Elsevier ClinicalKey Clinical Overview

Diagnosis CBC Indicated for all patients suspected of iron deficiency anemia In the United States, nearly always performed using automated technology systems Directly measured values include: hemoglobin level (g/dL), RBC count (cells/mm³), and mean corpuscular volume (fL) Derived values (and therefore less accurate or useful) include hematocrit value, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration Hemoglobin is lower than normal value for sex and/or age, defined by WHO as follows: Children aged 6 months to 59 months: lower than 11 g/dL Children aged 5 to 11 years: lower than 11.5 g/dL Children aged 12 to 14 years: lower than 12 g/dL Adults and adolescents aged 15 years or older: Female patients who are not pregnant: lower than 12 g/dL Female patients who are pregnant: lower than 11 g/dL Male patients: lower than 13 g/dL Older patients: lower limit of reference range may be lower (hemoglobin levels lower than 12 g/dL in both sexes) RBC count Reference range is about 4 to 6 × 10⁶ RBCs/mm³ or μL; varies with age, sex, and population RBC counts below lower limit of reference range suggest presence of anemia RBC indices characterize anemia based on cell size (mean corpuscular volume), degree of hemoglobinization (mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration), and degree of cell size variability (RBC distribution width) Mean corpuscular volume Defined as mean volume of RBCs calculated from hematocrit and RBC count Less than 80 fL indicates microcytosis In about 40% of patients with early iron deficiency anemia, normocytic RBCs are noted; decreased mean corpuscular volume is a late finding

Terminology Based on presence or absence of anemia in the setting of iron deficiency, reflecting the change in hematologic parameters and iron levels as anemia develops Iron deficient, no anemia Hemoglobin: within reference range Mean corpuscular volume: within reference range RBC morphology: within reference range (ie, not hypochromic) Iron studies: Ferritin level lower than about 30 to 40 ng/mL (in older patients and in those with inflammatory states, ferritin may be higher, up to 100 ng/mL Serum iron level within reference range Total iron-binding capacity may be elevated Transferrin saturation level within reference range Iron deficient, mild anemia Hemoglobin: less than 2 standard deviations below reference range value for same age and sex but typically 9 g/dL or higher Mean corpuscular volume: remains within reference range initially but begins to decrease as anemia becomes more chronic RBC morphology: may be slightly hypochromic Iron studies: Ferritin level 20 ng/mL or less (in older patients and in those with inflammatory states, ferritin may be higher) Decreased serum iron level Increased total iron-binding capacity Decreased transferrin saturation level Iron deficient, severe anemia Hemoglobin: significantly less than 2 standard deviations below reference range value for same age and sex, typically 7 g/dL or lower Mean corpuscular volume: decreased RBC morphology: hypochromic Iron studies: Ferritin level lower than 10 ng/mL (in older patients and in those with inflammatory states, ferritin may be higher) Very low serum iron level Significantly increased total iron-binding capacity Significantly decreased transferrin saturation level Based on adequacy of iron stores Absolute iron deficiency Total body iron stores are low or absent Functional iron deficiency

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DeLoughery, Thomas G. (2024). In Goldman-Cecil Medicine (pp. 1082). DOI: 10.1016/B978-0-323-93038-3.00145-3

The serum ferritin level correlates with body iron stores in healthy patients and is the most reliable and cost-effective test to diagnose iron deficiency. Since ferritin is an acute phase reactant, an iron-replete patient may have a very high ferritin level, but it is rare for an iron-deficient patient to have a ferritin level over 100 ng/mL. A ferritin level of less than 15 ng/mL is very specific for iron deficiency, but iron deficiency cannot be excluded in older patients or in patients who have inflammatory conditions unless the ferritin level is greater than 100 ng/mL. Ferritin values under 50 ng/mL should be considered abnormal in a symptomatic patient. The anemia of iron deficiency is classically a microcytic anemia (Table 145-1) without reticulocytosis (Fig. 145-2), but these findings are neither sensitive nor specific (Table 145-3) since thalassemia and the anemia of inflammation (Chapter 144) can also lead to microcytosis. A low red cell mean corpuscular volume is generally a late finding seen with severe iron deficiency, but concurrent medical issues such as liver disease, folate deficiency, or B12deficiency (Chapter 144) may blunt or obscure the decrease in red cell size. A serum iron level is not effective as a diagnostic test since it is low in the anemia of inflammation, can be falsely elevated with oral iron intake in iron-deficient patients, and varies markedly from day to day. An elevated total iron binding capacity (TIBC) is specific for iron deficiency, but its sensitivity is low because it is reduced by inflammation, aging, and poor nutrition. Iron saturation percentages are also unreliable because they depend on both the TIBC and serum iron level, so saturation is also low in the anemia of chronic disease. Serum levels of soluble transferrin receptor are increased in iron deficiency, and levels also can be increased in any condition associated with increased red cell mass, such as in hemolytic anemias. The gold standard for iron deficiency is the bone marrow iron stain, but this invasive and expensive procedure is rarely, if ever, indicated.

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Elsevier ClinicalKey Clinical Overview

Diagnosis Iron studies Iron deficiency anemia: serum iron levels are low, ferritin level is low, and total iron binding capacity is high Anemia of chronic disease (inflammation): serum iron is low, ferritin level is normal or elevated ( greater than 12 ng/mL) When iron deficiency occurs in the setting of an inflammatory state, serum ferritin levels may be misleadingly high, as ferritin is an acute phase reactant Folate and vitamin B₁₂/methylmalonic acid levels Low levels are generally associated with macrocytic anemia, but anemia resulting from these deficiencies may be normocytic early in the course