Microcytic Anemia with Elevated RDW: Iron Deficiency Anemia
This patient has iron deficiency anemia (IDA) and requires serum ferritin measurement immediately, followed by comprehensive gastrointestinal evaluation if ferritin confirms iron deficiency.
Diagnosis
The laboratory values demonstrate classic iron deficiency anemia:
- Microcytosis (MCV 77 fL, normal >80 fL) 1
- Hypochromia (MCH 23.7 pg and MCHC 30.6 g/dL, both reduced)
- Elevated RDW (17%, normal <14-15%) indicating anisocytosis—the earliest morphologic change in iron deficiency 2
The elevated RDW is particularly significant here. RDW >15% has 71-82% sensitivity for iron deficiency and is often elevated before other parameters become abnormal 2, 3. The combination of low MCV and high RDW is highly characteristic of iron deficiency rather than other microcytic anemias like thalassemia (which typically shows normal or low RDW with elevated RBC count) 1, 4.
Immediate Evaluation Required
1. Confirm Iron Deficiency
Serum ferritin is the most powerful test for iron deficiency 1:
- Ferritin <12 μg/dL is diagnostic of iron deficiency
- Ferritin <15 μg/L confirms iron deficiency 5
- If ferritin 12-100 μg/dL with inflammation/malignancy, consider transferrin saturation <30% or therapeutic trial of oral iron for 3 weeks 1
2. Identify the Source (Critical for Morbidity/Mortality)
All patients with confirmed IDA require gastrointestinal evaluation unless there is obvious non-GI blood loss 1. This is essential because:
- Asymptomatic gastric and colonic carcinoma commonly present with IDA
- GI blood loss is the most common cause in men and post-menopausal women 1
Mandatory investigations 1:
- Upper GI endoscopy with small bowel biopsies (reveals cause in 30-50% of patients; detects celiac disease in 2-3% of IDA patients)
- Colonoscopy or barium enema to exclude colonic malignancy
The order depends on patient age and symptoms, but in elderly patients, investigate the colon first as it is more likely to be productive 1.
3. Obtain Detailed History
Look specifically for:
- Dietary iron intake (though borderline deficient diets are common and should not preclude full GI workup) 1
- NSAID/aspirin use (stop if possible but continue investigation) 1
- GI symptoms (though these rarely correlate with findings) 1
- Family history of thalassemia, sideroblastic anemia, or bleeding disorders 1
- Menstrual history in pre-menopausal women
- Previous gastric surgery 1
Common Pitfalls to Avoid
Do not assume dietary deficiency explains the anemia—full GI investigation is still required even with positive dietary history 1
Do not skip investigation in mild anemia—there is no evidence that mild anemia is less indicative of serious disease than severe anemia 1
Do not rely on hemoglobin and RBC indices alone—while RDW has 82% sensitivity and 97% specificity for iron deficiency 2, these parameters have significant overlap between iron-deficient and non-iron-deficient patients, especially in non-anemic individuals 6, 3
Consider combined deficiencies—microcytosis may be absent with concurrent folate deficiency, which can be recognized by elevated RDW 1
Rule out thalassemia in appropriate ethnic groups—confirm with laboratory testing rather than presuming based on ethnicity alone 1
In patients with chronic inflammation, malignancy, or liver disease, ferritin may be falsely elevated above 12-15 μg/dL despite true iron deficiency (though if >100 μg/dL, iron deficiency is almost certainly absent) 1
Treatment Approach
Once the underlying cause is identified and addressed, the anemia will resolve. Even when no cause is detected, the long-term outlook is good 1. However, identifying malignancy early is critical for mortality outcomes, making the comprehensive GI evaluation non-negotiable in this clinical scenario.