Evaluation and Management of Anemia When Serum Ferritin Is ≥ 30 µg/L

Diagnostic Approach

• Assess inflammation promptly by measuring CRP and ESR to determine whether an elevated ferritin reflects true iron stores or an acute‑phase response (Journal of Crohn’s and Colitis) 1, 2, 3.
• Obtain a complete blood count with MCV and reticulocyte count, and calculate transferrin saturation (TSAT) as (serum iron × 100) ÷ TIBC (Journal of Crohn’s and Colitis) 1, 2.

Interpreting Ferritin in the Context of Inflammation

• Ferritin 30–100 µg/L with elevated CRP/ESR indicates a mixed picture of true iron deficiency together with anemia of chronic disease (Journal of Crohn’s and Colitis) 1, 2, 3.
• A TSAT < 20 % confirms iron deficiency that requires treatment even when ferritin is as high as 100 µg/L (Journal of Crohn’s and Colitis) 1, 2, 3.
• Ferritin > 100 µg/L with elevated CRP/ESR points primarily to anemia of chronic disease (Journal of Crohn’s and Colitis) 1, 2, 3.
• Diagnostic criteria for anemia of chronic disease in this setting are ferritin > 100 µg/L AND TSAT < 20 % in the presence of inflammation (Journal of Crohn’s and Colitis) 1, 3.
• Functional iron deficiency may still be present despite high ferritin; a low TSAT (<20 %) reveals iron sequestration and unavailability for erythropoiesis (Journal of Crohn’s and Colitis) 2.
• When ferritin > 100 µg/L without inflammation, absolute iron deficiency is unlikely; ferritin > 150 µg/L rarely occurs with true iron deficiency (Journal of Crohn’s and Colitis) 1, 2.
• In the absence of inflammation, alternative causes of anemia such as vitamin B12 or folate deficiency, hemolysis, or bone‑marrow disease should be investigated (Journal of Crohn’s and Colitis) 1, 2.

Additional Diagnostic Tests for Discordant Results

• Measure soluble transferrin receptor (sTfR) when ferritin and TSAT provide conflicting information (Journal of Crohn’s and Colitis) 1.
• An elevated sTfR confirms true iron deficiency even in the setting of inflammation because sTfR is not an acute‑phase reactant (Journal of Crohn’s and Colitis) 1.
• A low or normal reticulocyte count suggests deficiency states or bone‑marrow failure and warrants further work‑up (Journal of Crohn’s and Colitis) 1, 2.
• Elevated reticulocytes argue against iron deficiency and point toward hemolysis; appropriate labs (haptoglobin, LDH, bilirubin) should be obtained (Journal of Crohn’s and Colitis) 1, 2.
• Increased RDW can reveal iron deficiency even when MCV is normal, reflecting coexistence of micro‑ and macrocytic cells (Journal of Crohn’s and Colitis) 1, 2.
• Macrocytosis raises suspicion for vitamin B12 or folate deficiency, medication effects (e.g., azathioprine), or reticulocytosis (Journal of Crohn’s and Colitis) 1, 2.

Treatment Recommendations

• For confirmed iron deficiency (ferritin 30–100 µg/L with TSAT < 20 %), initiate oral iron therapy promptly and concurrently treat the underlying inflammatory condition to facilitate iron mobilization (Journal of Crohn’s and Colitis) 1, 2.
• In anemia of chronic disease (ferritin > 100 µg/L, TSAT < 20 %, elevated CRP/ESR), the primary intervention is aggressive management of the underlying inflammatory disease (Journal of Crohn’s and Colitis) 1, 2, 3.

Special Population Considerations

• In patients with inflammatory bowel disease (IBD), a ferritin < 30 µg/L during remission reliably indicates iron deficiency (Journal of Crohn’s and Colitis) 1, 3.
• During active IBD inflammation, ferritin values up to 100 µg/L may still represent iron deficiency and should be evaluated with TSAT (Journal of Crohn’s and Colitis) 1, 3.
• For IBD, chronic kidney disease, and chronic heart failure, a ferritin threshold of < 100 µg/L (instead of < 30 µg/L) is recommended to screen for iron deficiency (Journal of Crohn’s and Colitis) 1, 3.

Serum Ferritin Levels for Diagnosing Iron Deficiency

Diagnostic Thresholds

• The European Crohn's and Colitis Organisation recommends that serum ferritin <30 μg/L is the appropriate diagnostic criterion for iron deficiency in patients without clinical, endoscopic, or biochemical evidence of active inflammation 4, 5, 6
• A cut-off of <15 μg/L is highly specific (specificity 0.99) for absolute iron deficiency, according to the British Society of Gastroenterology 7
• A serum ferritin threshold of <45 μg/L may provide optimal trade-off between sensitivity and specificity for iron deficiency in clinical practice, as suggested by the British Society of Gastroenterology 7

Diagnostic Parameters in Inflammatory Conditions

• In patients with inflammation, serum ferritin up to 100 μg/L may still be consistent with iron deficiency, as stated by the European Crohn's and Colitis Organisation 4, 5, 6, 8
• If serum ferritin is between 30-100 μg/L in the presence of inflammation, a combination of true iron deficiency and anemia of chronic disease is likely, according to the European Crohn's and Colitis Organisation 4, 5, 6
• Transferrin saturation (TSAT) <20% should be considered alongside ferritin for accurate diagnosis of iron deficiency, especially in inflammatory conditions, as recommended by the European Crohn's and Colitis Organisation 6, 8

Special Populations

Inflammatory Bowel Disease

• In IBD patients, the diagnostic criteria for iron deficiency depend on the level of inflammation, with serum ferritin <30 μg/L in remission and up to 100 μg/L in active disease, as stated by the European Crohn's and Colitis Organisation 4, 5, 9
• Regular monitoring is recommended: every 6-12 months in remission or mild disease, and at least every 3 months in patients with active disease, according to the European Society for Clinical Nutrition and Metabolism 9

Chronic Kidney Disease

• In CKD patients, absolute iron deficiency has been defined as serum ferritin <100 ng/mL and TSAT <20%, as defined by the National Kidney Foundation 10, 11
• Functional iron deficiency can occur despite normal or elevated serum ferritin levels, particularly in patients receiving erythropoiesis-stimulating agents, as noted by the National Kidney Foundation 11

Ferritin Threshold to Diagnose Iron Deficiency Anemia

Diagnostic Thresholds

• The American Gastroenterological Association recommends using a ferritin cutoff of <45 ng/mL to diagnose iron deficiency in patients with anemia, as this provides the optimal balance between sensitivity and specificity in clinical practice 12, 13
• Ferritin <45 ng/mL is the recommended diagnostic cutoff for iron deficiency anemia in patients without inflammatory conditions, with strong evidence supporting this threshold over the traditional <15 ng/mL cutoff 12, 13
• Ferritin <15 ng/mL has 99% specificity for absolute iron deficiency but misses many cases due to low sensitivity 14
• Ferritin <30 ng/mL generally indicates depleted iron stores and is the threshold recommended by European guidelines for patients without active inflammation 14
• The European guidelines suggest that ferritin >150 ng/mL is unlikely to represent absolute iron deficiency, even in the presence of inflammation, and should prompt consideration of alternative diagnoses 14

Diagnostic Algorithm

• If ferritin <15 ng/mL, absolute iron deficiency is confirmed, and further investigation into the source of blood loss is recommended 14
• If ferritin 15-45 ng/mL, iron deficiency is highly likely, and treatment and investigation should be initiated 12, 13, 14
• If ferritin 45-100 ng/mL, inflammatory markers such as CRP and ESR should be checked to determine the presence of inflammation 14

Critical Caveats

• Using the traditional ferritin cutoff of <15 ng/mL misses the majority of iron deficiency cases because this threshold has high specificity but poor sensitivity 12, 13, 14

Diagnostic Approach to Microcytic Hypochromic Anemia with Normal Ferritin

Initial Evaluation

• Measure inflammatory markers (CRP and ESR) promptly when ferritin is in the 30‑100 µg/L range to help differentiate true iron deficiency, anemia of chronic disease, or genetic iron‑metabolism disorders. 15
• Calculate transferrin saturation (TSAT) as (serum iron × 100) ÷ TIBC; a TSAT < 20 % confirms iron deficiency that warrants treatment even if ferritin is as high as 100 µg/L. 16

Interpretation of Results

When Inflammation Is Present (Elevated CRP/ESR)

• Ferritin 30‑100 µg/L and TSAT < 20 % indicates true iron deficiency co‑existing with anemia of chronic disease; start iron therapy while addressing the underlying inflammatory condition. 16
• Ferritin > 100 µg/L and TSAT < 20 % suggests anemia of chronic disease with functional iron deficiency; prioritize aggressive management of the inflammatory disease. 16

When Inflammation Is Absent (Normal CRP/ESR)

• Ferritin 30‑100 µg/L and TSAT < 20 % denotes true iron deficiency; initiate oral iron supplementation. 16

Genetic and Rare Disorders

• Iron‑refractory iron deficiency anemia (IRIDA) caused by TMPRSS6 mutations presents with very low TSAT, low‑to‑normal ferritin, and lack of response to oral iron. 15
• Before pursuing genetic testing for IRIDA, exclude autoimmune atrophic gastritis, Helicobacter pylori infection, and celiac disease, which can also cause oral‑iron refractoriness. 17
• Sideroblastic anemias due to mutations in SLC25A38, STEAP3, or ABCB7 show microcytic hypochromic anemia, elevated TSAT, and increased ferritin even prior to transfusion therapy. 18
• Confirmation of sideroblastic anemia requires bone‑marrow examination demonstrating ring sideroblasts; subsequent genetic testing identifies the specific mutation. 19
• Hypotransferrinemia from TF defects manifests early with microcytic hypochromic anemia, low serum iron, high ferritin, and fully saturated transferrin despite markedly reduced transferrin levels. 18

Common Pitfalls

• Normal‑range ferritin (up to 100 µg/L) does not exclude iron deficiency in the setting of inflammation; iron deficiency may still be present. 16
• Relying on ferritin alone is insufficient; always calculate TSAT because functional iron deficiency can exist with high ferritin when TSAT < 20 %. 16
• Failure to consider inherited iron‑metabolism disorders when anemia is refractory to iron therapy may miss conditions such as IRIDA; a family history and early onset should prompt further evaluation. 15

Special Population Considerations

• In inflammatory bowel disease, ferritin < 30 µg/L during remission reliably indicates iron deficiency, whereas during active inflammation ferritin values up to 100 µg/L may still represent iron deficiency. 16

Diagnostic Workup for Iron Deficiency Anemia

Minimum Required Laboratory Tests

• The essential initial panel for any patient suspected of anemia should include a complete blood count with red‑cell distribution width and mean corpuscular volume, a reticulocyte count, serum ferritin, calculated transferrin saturation, and C‑reactive protein to detect concurrent inflammation. 20

Hemoglobin Thresholds for Defining Anemia

• Apply the WHO hemoglobin cut‑offs: men < 13 g/dL, non‑pregnant women < 12 g/dL, pregnant women < 11 g/dL, and children ≈ 11–12 g/dL depending on age. 20

Ferritin Interpretation Without Inflammation (Normal CRP)

• In patients with normal CRP, a serum ferritin < 30 µg/L confirms iron deficiency. 20
• Ferritin < 12–15 µg/L yields ≈ 99 % specificity for iron deficiency, though sensitivity is limited. 21
• Ferritin > 100 µg/L essentially rules out iron deficiency when inflammation is absent. 21

Ferritin Interpretation With Inflammation (Elevated CRP/ESR)

• Because ferritin is an acute‑phase reactant, values up to 100 µg/L may still indicate iron deficiency in the presence of inflammation. 20
• Ferritin 30–100 µg/L together with elevated CRP suggests a mixed picture of true iron deficiency plus anemia of chronic disease. 22
• Ferritin > 100 µg/L combined with transferrin saturation < 20 % and elevated CRP defines anemia of chronic disease with functional iron deficiency. 22

Transferrin Saturation (TSAT) Thresholds

• A TSAT < 20 % is the primary cutoff to confirm iron deficiency, especially when ferritin lies between 30–100 µg/L. 20
• TSAT < 16 % together with low MCV, raised RDW, and microcytic‑hypochromic red cells on smear strongly supports iron deficiency anemia. 22
• In inflammatory states, the diagnostic criteria for anemia of chronic disease are ferritin > 100 µg/L and TSAT < 20 %. 22

Red Blood Cell Indices

• Microcytosis (MCV below the reference range) is typical of iron deficiency anemia but may be absent when multiple deficiencies coexist. 20
• Normocytic anemia with normal or elevated ferritin points toward anemia of chronic disease. 20
• An elevated RDW signals iron deficiency and can uncover concurrent micro‑ and macro‑cytosis that mask MCV changes. 20

Reticulocyte Count Interpretation

• Low or normal reticulocyte counts indicate an inadequate marrow response due to nutrient deficiencies (iron, B12, folate) or primary marrow disease. 20
• Elevated reticulocytes suggest increased red‑cell production, which excludes deficiency states and favors hemolysis. 20
• When reticulocytes are high, order haptoglobin, lactate dehydrogenase, and bilirubin to evaluate for hemolysis. 20

Extended Workup When Initial Tests Are Inconclusive

• Add vitamin B12 and folate measurements to rule out other macro‑cytic anemias. 20
• Soluble transferrin receptor (sTfR) is raised in true iron deficiency and is not affected by inflammation, aiding differentiation. 20
• Assess the percentage of hypochromic red cells and reticulocyte hemoglobin content for a more precise iron‑status evaluation. 20
• Evaluate renal function with serum creatinine and urea when anemia etiology remains unclear. 20

Special Population: Inflammatory Bowel Disease (IBD)

• In IBD patients in remission, ferritin < 30 µg/L reliably indicates iron deficiency. 22
• During active IBD inflammation, use ferritin < 100 µg/L as a screening threshold and confirm iron deficiency with TSAT < 20 %. 22

Common Pitfalls and Caveats

• Gastrointestinal blood loss from occult malignancy (colon or gastric cancer) is the most frequent cause of iron deficiency in adult men and post‑menopausal women; it must be investigated. 21
• Do not rely on ferritin alone when inflammation is present; always calculate TSAT because functional iron deficiency can exist with high ferritin but low TSAT. 22
• Mild anemia is not less indicative of serious underlying disease; no evidence supports down‑ranking its clinical significance. 21
• In chronic inflammation, malignancy, or hepatic disease, ferritin may be falsely elevated above 12–15 µg/L despite true iron deficiency. 21
• Patients with extensive small‑bowel resection, ileal Crohn’s disease, or an ileal‑anal pouch should have vitamin B12 and folate monitored more frequently than annually. 20

Diagnosis and Management of Iron Deficiency Anemia in Adults

Diagnostic Criteria

• In adults, a hemoglobin level below the WHO threshold for non‑pregnant women (< 12 g/dL) confirms anemia and warrants full evaluation, regardless of severity. 23
• A ferritin concentration < 15 µg/L (e.g., 8 µg/L) has ≈ 99 % specificity for absolute iron deficiency. 23
• Transferrin saturation < 20 % (e.g., 5 %) is a decisive marker confirming iron deficiency. [23][24]
• Microcytosis (MCV ≈ 70 fL) together with hypochromia (MCH ≈ 19 pg) are classic red‑cell changes of iron deficiency. 23
• An elevated red‑cell distribution width (> 14 %; e.g., 21 %) is an early and sensitive indicator of iron deficiency. 24
• When the above laboratory pattern is present, additional iron studies are unnecessary for diagnosis. 23

Investigation for Gastrointestinal Blood Loss

• In adults with iron deficiency anemia, gastrointestinal bleeding is the presumptive source until proven otherwise; occult malignancy must be excluded. 23
• Bidirectional endoscopy (upper endoscopy + colonoscopy) should be performed promptly because colorectal and gastric cancers are the most common serious causes in this age group. 23
• Endoscopic evaluation should not be delayed even if hemoglobin is above fast‑track referral thresholds (e.g., ≥ 10 g/dL for non‑menstruating women); investigation is indicated at any anemia level when iron deficiency is present. 23

Iron Replacement Therapy

• Oral elemental iron 100–200 mg daily should be started immediately while diagnostic work‑up proceeds. 23
• Therapy should continue for at least 3–6 months after hemoglobin normalization to fully replenish iron stores, aiming for ferritin > 50 µg/L. 23
• Intravenous iron is recommended when oral iron is poorly tolerated, malabsorption is documented, or hemoglobin fails to improve despite adherence. 23

Evaluation of Alternative Causes of Microcytosis

• If microcytosis persists after iron repletion—or if the patient belongs to an at‑risk ethnic group—hemoglobin electrophoresis should be ordered to exclude β‑thalassemia trait. 23
• Low ferritin effectively rules out anemia of chronic disease, which typically presents with ferritin > 100 µg/L, low total iron‑binding capacity, and transferrin saturation < 20 %. 24

Clinical Pitfalls to Avoid

• Do not attribute severe iron deficiency in perimenopausal adults solely to menstrual blood loss; gastrointestinal pathology must still be investigated. 23
• Do not discontinue iron supplementation once hemoglobin normalizes; iron stores must be restored (target ferritin > 50 µg/L) to prevent rapid recurrence. 23
• Do not diagnose thalassemia trait without first correcting iron deficiency, as the two conditions can coexist and iron deficiency can mask electrophoretic findings. 23
• Do not postpone endoscopic investigation while awaiting response to iron therapy; malignancy work‑up should proceed in parallel. 23

Anemia Evaluation and Iron Management Guidelines

1. Initial Diagnostic Workup for Anemia

• Order a complete blood count with red‑cell indices (MCV, MCH, RDW), absolute reticulocyte count, serum ferritin, transferrin saturation (TSAT), and C‑reactive protein (CRP) to classify anemia and guide treatment decisions. 25
• Measure vitamin B12 and folate levels in any patient with anemia, especially when MCV > 100 fL or iron studies are inconclusive. 25
• Obtain serum creatinine and estimated glomerular filtration rate (eGFR) to assess chronic kidney disease as a potential contributor. 25
• Perform thyroid function testing in patients with heart failure or unexplained anemia. 26

2. Iron‑Deficiency Anemia (IDA) Diagnosis

• When ferritin is 30–100 µg/L, a TSAT < 20 % is the primary confirmatory marker for true iron deficiency. 25

3. Intravenous Iron Therapy in Chronic Kidney Disease (CKD)

• For non‑dialysis CKD patients with anemia who are not receiving erythropoiesis‑stimulating agents (ESAs), consider IV iron if TSAT ≤ 30 % and ferritin ≤ 500 ng/mL to achieve a hemoglobin rise without initiating ESA therapy. 25
• A typical IV iron regimen is 500 mg administered initially, followed by a second 500 mg dose four weeks later. 25

4. Iron Management in Chronic Heart Failure (CHF)

• Evaluate all patients with chronic heart failure (NYHA class II–IV) for iron deficiency using serum iron, total iron‑binding capacity, and ferritin, irrespective of anemia status. 26
• Iron‑deficiency criteria in CHF are either ferritin < 100 ng/mL or ferritin 100–300 ng/mL together with TSAT < 20 %. 26
• Intravenous iron (e.g., ferric carboxymaltose or iron sucrose) improves functional capacity, quality of life, and NYHA class in iron‑deficient CHF patients. 26

5. Vitamin B12 and Folate Deficiency Management

• In macrocytic anemia (MCV > 100 fL), obtain serum vitamin B12 and folate levels to confirm deficiency. 25
• Treat confirmed vitamin B12 deficiency with appropriate oral or parenteral replacement therapy. 25
• For folate deficiency, prescribe 5 mg daily for 2 weeks, then 5 mg weekly for an additional 6 weeks. 25

6. Erythropoiesis‑Stimulating Agent (ESA) Initiation in CKD

• Initiate ESA therapy only after iron deficiency has been corrected and other reversible causes (vitamin B12/folate deficiency, blood loss, inflammation, malignancy, aluminum intoxication) have been excluded. 25
• Weigh the potential benefits of reducing transfusion requirements and anemia‑related symptoms against risks such as anaphylactoid reactions and uncertain long‑term safety. 25

Interpretation and Management of Anemia of Chronic Disease in Enteric Fever

Pathophysiology

• Inflammatory cytokines (especially IL‑6) stimulate hepatic hepcidin production, which blocks iron release from macrophages, hepatocytes, and enterocytes, leading to hypoferremia and iron sequestration despite adequate total body iron stores. 27, 28

Laboratory Interpretation

Ferritin as an Acute‑Phase Reactant

• Ferritin rises during inflammation and therefore masks the true iron status; an elevated ferritin does not necessarily indicate sufficient iron stores in the setting of infection. 27, 28

Transferrin Saturation (TSAT)

• A TSAT < 20 % in the presence of inflammation confirms functional iron deficiency, even when ferritin is elevated. 27, 28, 29

Combined Ferritin‑TSAT Criteria

• When ferritin > 100 µg/L and TSAT < 20 % during an inflammatory state, the diagnosis is anemia of chronic disease with functional iron deficiency. 27, 28, 29
• In inflammatory conditions, ferritin values up to 100 µg/L may still represent true iron deficiency; values between 30–100 µg/L suggest a mixed picture of iron deficiency plus anemia of chronic disease. 27, 28, 29, 30

Diagnostic Findings in Enteric Fever‑Associated Anemia

All laboratory values are derived from studies of patients with enteric fever‑related anemia of chronic disease. 27, 28, 29, 30, 31

Management Strategies

Primary Treatment

• Aggressive antimicrobial therapy targeting the underlying enteric fever is the cornerstone; controlling inflammation permits mobilization of sequestered iron stores. 28, 29

Iron Supplementation Decision

• Iron supplementation is not the primary intervention when ferritin > 100 µg/L with TSAT < 20 % in acute inflammation; treatment should focus on infection control. 27, 28, 29

Post‑Treatment Assessment

• After successful antibiotic therapy, re‑measure CBC, iron studies, and inflammatory markers (CRP, ESR). 27, 31
• If ferritin falls to 30–100 µg/L while TSAT remains < 20 % after inflammation resolves, true iron deficiency is present and iron supplementation should be initiated. 27, 28, 29

Critical Pitfalls to Avoid

• Do not interpret an elevated ferritin (> 100 µg/L) during acute infection as evidence of adequate iron stores; it reflects inflammation. 27, 28
• Do not start empiric iron solely based on low hemoglobin when ferritin is elevated and infection is active; iron will not be utilized until inflammation subsides. 28, 29
• Do not rely on ferritin alone in the presence of inflammation; always calculate TSAT to assess functional iron availability. 27
• Do not assume the anemia will self‑correct; monitor hemoglobin response after infection treatment, as underlying iron deficiency may become apparent once inflammation resolves. 28, 31

Diagnostic Work‑up for Iron Deficiency Anemia

Initial Laboratory Evaluation

• Order a complete blood count with red‑cell indices (MCV, MCH, RDW), a reticulocyte count, serum ferritin, transferrin saturation (TSAT), and C‑reactive protein (CRP) to simultaneously confirm anemia, assess iron status, and detect inflammation. 32
• CBC with MCV < 80 fL, MCH < 27 pg, and RDW > 14 % strongly suggests iron deficiency rather than thalassemia trait. 32
• Serum ferritin is the single most powerful test; a level < 30 µg/L confirms depleted iron stores in patients without inflammation. 32
• TSAT < 20 % is the primary confirmatory marker for iron deficiency, especially when ferritin lies between 30–100 µg/L or may be falsely elevated by inflammation. 32
• CRP (or ESR) is required to identify inflammation, which can raise ferritin up to ≈ 100 µg/L despite true iron deficiency. 32
• Reticulocyte count distinguishes inadequate marrow response (low/normal) in iron deficiency from hemolysis (elevated). 32

Interpretation of Ferritin Thresholds

• Ferritin < 15 µg/L provides 99 % specificity for absolute iron deficiency, confirming the diagnosis without further testing. 32
• Ferritin 30–100 µg/L together with elevated CRP/ESR suggests a mixed picture of true iron deficiency plus anemia of chronic disease; confirmation requires TSAT < 20 %. 32
• Ferritin > 100 µg/L with TSAT < 20 % and elevated CRP defines anemia of chronic disease with functional iron deficiency, not true iron deficiency. 32
• Ferritin > 150 µg/L makes absolute iron deficiency unlikely even in the presence of inflammation. 32

Transferrin Saturation (TSAT)

• TSAT < 16–20 % confirms iron‑deficient erythropoiesis and is decisive when ferritin is equivocal or falsely elevated by inflammation, malignancy, or liver disease. 32
• TSAT is more sensitive than hemoglobin alone for detecting iron deficiency. 32

Extended Testing When Initial Results Are Inconclusive

• Soluble transferrin receptor (sTfR) measurement is recommended when ferritin and TSAT give conflicting information; an elevated sTfR confirms true iron deficiency because it is not affected by inflammation. 32
• Percentage of hypochromic red cells and reticulocyte hemoglobin content provide more precise iron‑status evaluation when standard tests are borderline. 32
• Vitamin B12 and folate levels should be obtained to exclude megaloblastic anemia, which can coexist with iron deficiency and produce a mixed micro‑ and macrocytic picture with elevated RDW. 32
• Macrocytosis (MCV > 100 fL) raises suspicion for vitamin B12/folate deficiency, certain medications, or reticulocytosis. 32
• When reticulocytes are elevated, order haptoglobin, lactate dehydrogenase, and bilirubin to evaluate for hemolysis, which excludes pure iron‑deficiency states. 32
• Serum creatinine and urea should be measured when the anemia etiology remains unclear, as chronic kidney disease contributes to anemia via reduced erythropoietin and functional iron deficiency. 32

Special Populations

• In patients with inflammatory bowel disease (IBD) in remission, ferritin < 30 µg/L reliably indicates iron deficiency. 32
• During active IBD inflammation, ferritin < 100 µg/L is used as a screening threshold; iron deficiency is confirmed with TSAT < 20 %. 32

Diagnostic Algorithm (Key Steps)

• No inflammation (normal CRP) → ferritin < 30 µg/L confirms iron deficiency.
• Inflammation present (elevated CRP) → ferritin 30–100 µg/L with TSAT < 20 % indicates iron deficiency; ferritin > 100 µg/L with TSAT < 20 % indicates anemia of chronic disease. 32

Critical Pitfalls to Avoid

• Do not rely on ferritin alone when inflammation is present; always calculate TSAT because functional iron deficiency can coexist with high ferritin but low TSAT. 32
• Do not overlook combined deficiencies; iron deficiency can coexist with vitamin B12 or folate deficiency, recognizable by an elevated RDW. 32