Iron Deficiency Without Anemia
This patient has iron deficiency without anemia (non-anemic iron deficiency), as evidenced by low MCV (80.4 fL), low MCH (25.9 pg), and low transferrin saturation (14%), despite hemoglobin remaining within normal range at 13.1 g/dL.
Diagnosis
The laboratory findings clearly indicate iron deficiency based on multiple parameters:
- Transferrin saturation of 14% is below the diagnostic threshold of 16% that indicates iron deficiency 1, 2
- Low MCV (80.4 fL) and low MCH (25.9 pg) demonstrate microcytosis and hypochromia, which are characteristic red cell changes in iron deficiency 1
- Normal TIBC (368 mcg/dL) with low serum iron (50 mcg/dL) creates the classic pattern of iron deficiency
The British Society of Gastroenterology guidelines emphasize that MCH may actually be more reliable than MCV for detecting iron deficiency, as it's less dependent on the counting machine and shows reduction in both absolute and functional iron deficiency 1. Both parameters are abnormally low in this case.
Critical Missing Test
A serum ferritin level is essential to confirm the diagnosis and guide management. The guidelines specify that ferritin <15 μg/L is highly specific (0.99) for iron deficiency, while levels <45 μg/L warrant investigation, especially with chronic inflammation 1. Without ferritin, the diagnosis remains presumptive, though highly likely given the constellation of findings.
Why This Is Not Anemia
The hemoglobin of 13.1 g/dL exceeds the WHO threshold of 120 g/L (12.0 g/dL) for non-pregnant women or 130 g/L (13.0 g/dL) for men 1. This represents the early phase of iron deficiency where body iron stores are depleted (causing the low transferrin saturation and red cell changes) but hemoglobin concentration remains normal 1.
Recommended Workup
Immediate Steps:
- Order serum ferritin to quantify iron stores and confirm iron deficiency
- Investigate the underlying cause - The guidelines strongly recommend GI investigation for iron deficiency even without anemia, as the case is stronger with any degree of abnormality when iron deficiency is present 1
- Consider Hb electrophoresis if ferritin returns normal, to exclude thalassemia trait (which can cause similar microcytosis with normal iron studies), particularly if appropriate ethnic background 1
Investigation Algorithm:
- If ferritin <15 μg/L: Confirms absolute iron deficiency → investigate for GI blood loss, malabsorption, or inadequate dietary intake
- If ferritin 15-45 μg/L: Likely iron deficiency → still warrants investigation, especially if chronic inflammatory process present
- If ferritin >45 μg/L: Consider alternative diagnoses including thalassemia trait, anemia of chronic disease, or sideroblastic anemia
Treatment Approach
Initiate oral iron supplementation while pursuing diagnostic workup for the underlying cause. The transferrin saturation of 14% with elevated RDW (14.9%) indicates active iron-deficient erythropoiesis that will respond to iron therapy.
Common Pitfalls to Avoid:
- Don't dismiss this as "borderline normal" - The combination of low transferrin saturation, microcytosis, and hypochromia represents true iron deficiency requiring investigation
- Don't assume dietary insufficiency alone - Even without anemia, iron deficiency in adults warrants evaluation for occult GI blood loss, particularly colorectal pathology 1
- Don't rely solely on serum iron and TIBC - These have limited predictive value compared to ferritin and red cell indices 3. The transferrin saturation <16% has only 61% sensitivity and 86% specificity for iron deficiency 4
- Don't overlook the slightly elevated RDW (14.9%) - This suggests a mixed red cell population with emerging microcytic cells, supporting active iron-deficient erythropoiesis
The elevated TIBC (368 mcg/dL, upper normal range) combined with low iron creates the classic "high capacity, low cargo" pattern of iron deficiency, where the body attempts to maximize iron uptake by increasing transferrin production 2.