Management of Progressively Increasing RDW Values
Your patient's progressively rising RDW (now 16.10) is a red flag for evolving iron deficiency anemia that demands immediate confirmation with serum ferritin and comprehensive gastrointestinal investigation if confirmed. 1, 2
Immediate Diagnostic Steps
Obtain serum ferritin immediately—this is the single most powerful confirmatory test. 2
- Ferritin <30 μg/L confirms iron deficiency in the absence of inflammation 3, 1
- Ferritin <100 μg/L may still indicate iron deficiency if concurrent inflammation, malignancy, or hepatic disease is present 3, 2
- Ferritin <12 μg/L is diagnostic of iron deficiency regardless of inflammatory status 1
- Transferrin saturation (<30% supports iron deficiency) 1, 2
- C-reactive protein (CRP) to interpret ferritin correctly in inflammatory states 3, 4
- Complete blood count with MCV and reticulocyte count 3, 1
Understanding Your Patient's Rising RDW
The progressive increase in RDW reflects worsening anisocytosis as iron stores become progressively depleted, creating a mixed population of older normal-sized cells and newer microcytic cells. 2, 5
- RDW >14% is highly suggestive of iron deficiency rather than thalassemia trait (which typically shows normal or minimally elevated RDW) 1, 2, 6
- RDW becomes abnormal earlier than MCV in developing iron deficiency—it can rise 4+ weeks before MCV changes 5
- Even with normal MCV, elevated RDW strongly suggests iron deficiency, particularly if combined deficiencies (iron plus B12/folate) coexist 1, 2
Critical Pitfall: Do Not Skip GI Investigation
If iron deficiency is confirmed and your patient is an adult male or post-menopausal female, complete gastrointestinal evaluation is mandatory regardless of symptom presence or anemia severity. 1, 2
This requires: 2
- Upper endoscopy with mandatory small bowel biopsies (to exclude malignancy and detect coeliac disease, present in 2-3% of IDA patients)
- Colonoscopy or CT colonography (to exclude colonic cancer/polyps)
Common GI sources to investigate: 1, 2
- NSAID use (stop whenever possible)
- Colorectal cancer/polyps
- Gastric cancer
- Angiodysplasia
- Coeliac disease
- Inflammatory bowel disease
Do not attribute IDA to dietary causes without investigation—GI blood loss is the most common cause in adult men and post-menopausal women. 1
Treatment Protocol
Initiate oral iron supplementation immediately once iron deficiency is confirmed (ferritin <30 μg/L). 2, 4
- Ferrous sulfate 324 mg daily (equivalent to 65 mg elemental iron) 7
- Continue for 3-6 months after hemoglobin normalizes to replete iron stores 2
- Recheck CBC in 4-6 weeks to confirm reticulocyte response and declining RDW 4
A therapeutic trial can also serve diagnostic purposes: response to three weeks of oral iron confirms true iron deficiency if diagnostic uncertainty remains. 1
Additional Considerations
Document and address medication history: 1
- Stop NSAIDs and aspirin whenever possible
- Anticoagulant use should not deter investigation
Check reticulocyte count to assess bone marrow response: 3
- Low or "normal" reticulocytes with anemia indicate inability to respond properly (deficiency or bone marrow disease)
- Increased reticulocytes exclude deficiency states and suggest hemolysis
Do not overlook combined deficiencies—iron deficiency can coexist with folate or B12 deficiency, which may normalize MCV but maintain elevated RDW. 1, 2