What anemia presents with a low red blood cell count, low hemoglobin, low hematocrit, and a high red cell distribution width?

Anemia with Low RBC, Hemoglobin, Hematocrit, and High RDW

The pattern of low RBC count, low hemoglobin, low hematocrit, and elevated RDW (>14.0%) is most characteristic of iron deficiency anemia. 1

Understanding the Laboratory Pattern

High RDW indicates heterogeneous red cell populations with significant variation in cell size (anisocytosis), which is the hallmark of iron deficiency anemia. 1 This occurs because as iron stores become progressively depleted, newly produced red cells become increasingly microcytic while older cells remain normal-sized, creating a mixed population. 2

The CDC guidelines specifically state that a low MCV combined with RDW greater than 14.0% indicates iron-deficiency anemia, distinguishing it from other causes of microcytosis like thalassemia minor (which typically has low or normal RDW due to uniformly small cells). 1

Differential Diagnosis Based on RDW

High RDW Pattern (Your Scenario)

• Iron deficiency anemia: Most likely diagnosis with elevated RDW 1, 2
• Vitamin B12 or folate deficiency: Can present with high RDW, though 31% may have normal RDW 3
• Combined deficiencies: Iron plus folate or B12 deficiency may show elevated RDW with normal MCV 1, 4

Low RDW Pattern (Opposite of Your Scenario)

• Thalassemia trait: Typically presents with low or normal RDW due to homogeneous microcytic cells 1, 4
• Anemia of chronic disease: Often shows normal or low RDW 5, 4

Diagnostic Workup Algorithm

When you encounter this laboratory pattern, proceed systematically:

1. Confirm iron deficiency with serum ferritin (<12-30 μg/L diagnostic; <100 μg/L if inflammation present) 1, 4

2. Measure transferrin saturation (<30% supports iron deficiency) 1, 4

3. Check inflammatory markers (CRP) to assess whether ferritin elevation reflects inflammation rather than adequate iron stores 4

4. Consider combined deficiencies by checking B12 and folate levels, especially if MCV is normal despite anemia 1, 4

5. Perform peripheral blood smear to assess red cell morphology and confirm anisocytosis 5

Clinical Correlation with Severity

The degree of RDW elevation inversely correlates with hemoglobin level and transferrin saturation in iron deficiency anemia - higher RDW values indicate more severe iron depletion. 2 Studies show RDW is elevated in 100% of severe IDA cases, 82% of moderate cases, and 100% of mild cases, making it more sensitive than peripheral smear morphology for detecting early iron deficiency. 6

Critical Management Points

Do not assume iron deficiency based solely on anemia - confirm with ferritin testing before initiating treatment. 4 However, when high RDW accompanies low hemoglobin, iron deficiency is highly likely and warrants immediate investigation. 1, 2

All adult men and post-menopausal women with confirmed iron deficiency require gastrointestinal evaluation (upper and lower endoscopy) to exclude malignancy, regardless of symptom presence or anemia severity. 1, 4

Avoid empirical iron supplementation without confirming the diagnosis, as this can cause harm in conditions like thalassemia that may occasionally present with elevated RDW. 4, 7

Common Pitfalls to Avoid

• Do not rely on MCV alone - combined deficiencies can normalize MCV despite iron deficiency, but RDW remains elevated 1, 4
• Do not assume mild anemia is less significant - severity does not correlate with likelihood of serious underlying disease requiring investigation 1, 4
• Do not attribute microcytosis to thalassemia in certain ethnic groups without laboratory confirmation, especially when RDW is elevated (thalassemia typically has normal/low RDW) 1, 4