Laboratory Assessment of Iron Deficiency Anemia

Core Laboratory Panel

Order a complete blood count (CBC) with hemoglobin, hematocrit, and white‑cell differential, red‑cell indices (MCV, MCH, RDW), reticulocyte count, serum ferritin, transferrin saturation, and C‑reactive protein (CRP) to reassess iron deficiency anemia. 1, 2
Serum ferritin is the most powerful single test for detecting iron deficiency. 1, 2, 3
Transferrin saturation provides a direct measure of iron available for erythropoiesis and is less affected by inflammation than ferritin. 1, 2
CRP should be measured concurrently because inflammation can falsely elevate ferritin, obscuring iron‑deficiency diagnosis. 1, 2

In patients without inflammation, a serum ferritin < 30 µg/L confirms iron deficiency. 1, 4, 5, 3
In the presence of inflammation, ferritin values up to 100 µg/L may still indicate iron deficiency because ferritin is an acute‑phase reactant. 1, 4, 5, 3
A transferrin saturation < 20 % signals functional or absolute iron deficiency regardless of inflammatory status. 1, 6
Ferritin > 100 µg/L together with transferrin saturation < 20 % suggests anemia of chronic disease. 4, 5
Ferritin values between 30–100 µg/L with concurrent inflammation are most consistent with a mixed picture of iron deficiency and anemia of chronic disease. 4, 5

Measure vitamin B12 and folate to exclude concurrent nutritional deficiencies, especially if MCV is elevated or remains normal despite suspected iron deficiency. 1, 2, 5
Assess haptoglobin and lactate dehydrogenase (LDH) to evaluate for hemolysis when the reticulocyte count is elevated. 1, 2, 5
Determine the percentage of hypochromic red cells and reticulocyte hemoglobin content for a more sensitive detection of functional iron deficiency (requires specialized equipment). 1, 6
Use soluble transferrin receptor (sTfR) testing to differentiate iron deficiency from anemia of chronic disease in inflammatory conditions. 1, 6
Check creatinine and urea to identify a renal contribution to anemia. 1

An RDW > 14 % points toward iron deficiency even when MCV appears normal, because coexisting macrocytosis and microcytosis can mask each other. 1, 3
Mean corpuscular hemoglobin (MCH) is more reliable than MCV for detecting iron deficiency, as it is less dependent on sample handling and analyzer variability. 3
A low or “normal” reticulocyte count in the setting of anemia indicates an inadequate bone‑marrow response, favoring deficiency states or primary marrow disease. 1, 2
An elevated reticulocyte count effectively excludes deficiency‑related anemia and instead suggests hemolysis or acute blood loss. 1, 2
When microcytosis is present with normal iron studies, hemoglobin electrophoresis should be performed to rule out thalassemia, particularly in at‑risk ethnic groups. 3

Do not rely solely on hemoglobin and hematocrit, as they are late indicators and miss early iron depletion. 7
Do not interpret ferritin without a concurrent CRP measurement; inflammation can falsely elevate ferritin and mask iron deficiency. 1
Do not assume a normal MCV excludes iron deficiency; combined deficiencies (e.g., iron plus B12/folate) can yield a normal MCV with an elevated RDW. 1, 3
Do not omit transferrin saturation testing; it is less influenced by inflammation and may be the only abnormal parameter in functional iron deficiency. 8, 6
Do not proceed to bone‑marrow examination before completing the extended biochemical workup and obtaining hematology consultation. 1, 2

The American College of Physicians recommends a complete blood count (CBC) with red cell indices, including mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and red cell distribution width (RDW), as essential components of anemia diagnosis 9
Hemoglobin and hematocrit serve as screening tests but are late indicators of deficiency states 9
MCV measures average red blood cell size and is essential for classifying anemia as microcytic, normocytic, or macrocytic 9
RDW is critical for detecting mixed deficiencies, with elevated RDW >14.0% suggesting iron deficiency anemia 9
MCH provides a sensitive indication of iron deficiency, with low levels indicating iron depletion 9
Reticulocyte count distinguishes between production defects versus hemolysis or blood loss, with elevated reticulocytes indicating increased red blood cell production 9

Serum ferritin is the most powerful single test for diagnosing iron deficiency, with levels <30 μg/L indicating iron deficiency 9
Transferrin saturation represents iron available for erythropoiesis, with <20% indicating functional or absolute iron deficiency 9
Serum iron and total iron-binding capacity (TIBC) are measured together to calculate transferrin saturation, with low serum iron and high TIBC indicating iron deficiency 9
Ferritin is an acute-phase reactant and may be falsely elevated in inflammatory conditions, requiring a higher threshold (<100 μg/L) to diagnose iron deficiency in these patients 9
C-reactive protein (CRP) should be measured alongside ferritin to assess for inflammation that could confound interpretation 9

Serum vitamin B12 and folate levels are essential components of the anemia profile 9, 10
Methylmalonic acid (MMA) is a sensitive marker for B12 deficiency, often elevated early in the condition 11
Homocysteine levels are also elevated in B12 deficiency, providing additional confirmatory evidence 11
Unlike iron studies, inflammatory conditions do not significantly affect interpretation of B12 testing 11

Erythrocyte protoporphyrin concentration detects earlier changes in iron status than hemoglobin or hematocrit, with elevated levels indicating iron deficiency 9
Soluble transferrin receptor (sTfR) may help distinguish iron deficiency anemia from anemia of chronic disease, particularly in patients with liver disease or inflammatory conditions 9
Reticulocyte hemoglobin content (CHr) and percent hypochromic red blood cells (PHRBC) are specialized tests with high sensitivity and specificity for functional iron deficiency 9
A thorough drug exposure history is necessary to identify chemotherapy-related causes of anemia in cancer patients 10
Assessment of occult blood loss and renal insufficiency is crucial in cancer-specific anemia workup 10
Baseline erythropoietin level, serum thyroid-stimulating hormone level, direct antiglobulin testing (Coombs test), and hemoglobinopathy screening may be necessary in specific cases 10

Do not rely solely on MCV for classification, as coexisting conditions may neutralize MCV changes 9
Do not misinterpret ferritin without considering inflammatory status, as this leads to incorrect diagnosis in patients with chronic disease 9
Do not fail to investigate underlying causes of deficiencies, particularly gastrointestinal bleeding in iron deficiency 9