Elevated RDW Suggests Possible Iron Deficiency or Mixed Anemia Requiring Further Workup
These lab values show normal hemoglobin (14.2 g/dL) and MCHC (31.5 g/dL) but significantly elevated RDW (17.8%), which indicates increased red cell size variation (anisocytosis) and warrants investigation for iron deficiency, combined nutritional deficiencies, or early hematologic abnormalities.
Interpretation of Your Values
Your hemoglobin is normal, ruling out overt anemia. The MCHC is within normal range (32-36 g/dL), indicating adequate hemoglobin concentration within red cells. However, the RDW of 17.8% is markedly elevated (normal range typically 11.5-14.5%), which is the critical finding here.
Clinical Significance of Elevated RDW
An elevated RDW with normal hemoglobin and MCHC most commonly indicates:
- Early or evolving iron deficiency - RDW rises before anemia develops, as it reflects the earliest morphologic changes in iron deficiency 1
- Combined nutritional deficiencies - Microcytosis may be masked by concurrent folate or B12 deficiency, recognized by raised RDW 1
- Chronic disease states - Inflammation affecting iron utilization
- Hemoglobinopathies - Though less likely with normal MCHC
The elevated RDW has 82.3% sensitivity and 97.4% specificity for detecting iron deficiency, making it more sensitive than hemoglobin (56.6%), MCV (29.2%), or MCHC (15%) for early detection 2. RDW appears to be a reliable early marker, rising before other parameters become abnormal 2, 3.
Required Next Steps
You must obtain serum ferritin immediately - this is the most powerful test for iron deficiency 1. A ferritin <12 μg/dL is diagnostic of iron deficiency, though values <15 μg/dL are also considered deficient in many contexts 1.
Additional Essential Tests:
- Complete iron panel: Transferrin saturation (<30% suggests deficiency) 1
- MCV and MCH: To assess red cell size and hemoglobin content
- Reticulocyte count: To evaluate bone marrow response 4
- Consider vitamin B12 and folate levels: Given possibility of combined deficiency 1
Critical Caveat About Ferritin:
Ferritin can be falsely elevated (>12-15 μg/dL) in the presence of inflammation, malignancy, or liver disease, even when iron deficiency exists. However, if ferritin is >100 μg/dL, iron deficiency is almost certainly not present 1.
If Iron Deficiency is Confirmed
In adult men and post-menopausal women, gastrointestinal blood loss is the most common cause and requires investigation 1. You should undergo:
- Upper endoscopy with small bowel biopsies - 30-50% diagnostic yield; biopsies detect celiac disease in 2-3% of cases 1
- Colonoscopy or barium enema - Essential even if upper endoscopy is positive, as dual pathology occurs in ~10% 1
Common GI causes include NSAID use, colonic cancer/polyps, angiodysplasia, gastric cancer, celiac disease, and inflammatory bowel disease 1.
Important Pitfalls to Avoid
- Don't assume dietary insufficiency alone - Even with poor diet history, full GI investigation is required in adults 1
- Don't stop investigation if taking NSAIDs or anticoagulants - Document use but continue workup 1
- Don't ignore normal hemoglobin - Mild abnormalities are equally indicative of serious disease 1
- Consider ethnic background - Hemoglobinopathies (thalassemia, HbE) can cause elevated RDW but should be confirmed by hemoglobin electrophoresis or HPLC, not presumed 1, 5, 6
Bottom Line
Your elevated RDW is an early warning sign that should not be dismissed despite normal hemoglobin. Start with serum ferritin and complete iron studies now. If iron deficiency is confirmed and you are a man or post-menopausal woman, proceed directly to bidirectional GI evaluation to exclude malignancy and other serious pathology.