What is the most likely diagnosis based on serum iron 51 µg/dL, total iron‑binding capacity 359 µg/dL, transferrin saturation 14 %, and ferritin 41 ng/mL?

Iron Deficiency Anemia

Based on these laboratory values—serum iron 51 µg/dL, TIBC 359 µg/dL, transferrin saturation 14%, and ferritin 41 ng/mL—the most likely diagnosis is iron deficiency anemia.

Diagnostic Interpretation

Transferrin Saturation Calculation and Significance

• Your transferrin saturation of 14% falls well below the diagnostic threshold of 16–20%, confirming inadequate iron delivery to the bone marrow for red blood cell production 1, 2.
• A transferrin saturation <20% is the primary marker that confirms iron deficiency, particularly when ferritin values are in the equivocal range of 30–100 µg/L 1, 2, 3.

Ferritin Interpretation

• Your ferritin of 41 ng/mL sits in the diagnostic gray zone between 30–100 µg/L 1, 2.
• In the absence of inflammation (which must be confirmed by checking CRP and ESR), a ferritin <45 ng/mL provides optimal diagnostic accuracy for iron deficiency 3.
• The traditional cutoff of ferritin <15 µg/L has 99% specificity but misses the majority of iron deficiency cases due to poor sensitivity 1, 3.
• Ferritin between 30–100 µg/L combined with transferrin saturation <20% indicates true iron deficiency 2, 3.

Critical Next Step: Assess for Inflammation

• You must measure CRP and ESR immediately to determine whether ferritin is elevated by an acute-phase response 1, 2.
• If CRP/ESR are elevated, ferritin 30–100 µg/L with transferrin saturation <20% indicates a mixed picture of true iron deficiency plus anemia of chronic disease 1, 2.
• If CRP/ESR are normal, your ferritin of 41 ng/mL with transferrin saturation 14% confirms straightforward iron deficiency anemia 2, 3.

Diagnostic Algorithm

Without Inflammation (Normal CRP/ESR)

• Ferritin 41 ng/mL + transferrin saturation 14% = Iron deficiency anemia 2, 3.
• Initiate oral iron supplementation immediately 1.
• Investigate the source of iron loss—gastrointestinal blood loss from occult malignancy (colon or gastric cancer) is the most common cause in adult men and postmenopausal women 1, 3.

With Inflammation (Elevated CRP/ESR)

• Ferritin 30–100 µg/L + transferrin saturation <20% + elevated CRP = Combined iron deficiency and anemia of chronic disease 1, 2.
• Start iron therapy while simultaneously treating the underlying inflammatory condition 2, 3.
• The inflammatory process impairs iron mobilization from stores, so addressing inflammation is essential for treatment success 1, 2.

Supporting Laboratory Findings

• Your elevated TIBC of 359 µg/dL is consistent with iron deficiency, as the body increases transferrin production to capture any available iron 4, 5, 6.
• An elevated TIBC occurs before serum iron drops during the development of iron deficiency, representing a compensatory mechanism to mobilize tissue iron 5.
• The combination of low serum iron, high TIBC, and low transferrin saturation is highly specific for iron deficiency 4, 7.

Common Pitfalls to Avoid

• Do not dismiss iron deficiency simply because ferritin is above 30 µg/L—ferritin up to 100 µg/L may still represent iron deficiency when inflammation is present 1, 2.
• Do not rely on ferritin alone; always calculate transferrin saturation because functional iron deficiency can exist with normal-range ferritin when transferrin saturation is low 2, 3.
• Do not assume mild anemia is less clinically significant—no evidence supports downgrading its importance, as it may indicate serious underlying disease such as gastrointestinal malignancy 1, 3.

Additional Workup if Diagnosis Remains Unclear

• If inflammatory markers and transferrin saturation provide conflicting information, measure soluble transferrin receptor (sTfR), which is elevated in true iron deficiency and unaffected by inflammation 1, 2, 8.
• Check complete blood count with MCV and RDW—microcytosis and elevated RDW support iron deficiency 1, 3.
• Obtain reticulocyte count, vitamin B12, and folate to exclude other causes of anemia 1, 3.