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Iron Deficiency Anemia: Sensitivity and Specificity

Introduction: This is anemia caused by low total body iron stores (e.g. from a GI bleed). Gold standard of diagnosis is Prussian Blue staining of a bone marrow biopsy (rarely done). Generally iron deficiency results in a microcytic, hypochromic anemia. The transferrin levels (aka TIBC) are increased, ferritin levels (which measure bone marrow stores) are decreased, and iron saturation is decreased.

In contrast, Anemia of Chronic Disease (inflammation) causes an anemia from poor mobilization of iron stores. These patients have increased iron stores and thus high ferritin (ferritin is also high because it is an acute phase reactant) and usually low transferrin levels.

Ferritin has been shown to be the most accurate test to distinguish these, even in a mixed clinical picture (see the J Gen Intern Med paper).

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Tags: Hematologic Tag this Diagnosis.

Differential Diagnoses include: Anemia of Chronic Disease, Thalassemia

The sensitivity and specificity of findings for Iron Deficiency Anemia are listed below. See the left navigation bar to change the display.

Sensitive and Specific Findings

Finding SensitivitySpecificity Comments, Study
Decreased Ferritin
Duplicate Edit
85%92%

<45 ng/ml

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Specific Findings

Finding SensitivitySpecificity Comments, Study
Low Transferrin Saturation
Duplicate Edit
24%98%

<5%

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Decreased Ferritin
Duplicate Edit
73%97%

<25ng/ml

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Red Cell Protoporphyrin Edit 31%96%

>250mcg/dl

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Decreased Ferritin
Duplicate Edit
80%95%

<35ng/ml

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

RDW, increased
Duplicate Edit
13%95%

>21

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Decreased MCV Edit 42%93%

<75um^3.

FYI, for <80um^3 (usual lower limit of normal) sens = 54%, spec = 81%.

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

RDW, increased
Duplicate Edit
82%89%

RDW > 18 for iron deficiency vs b-thal

note that other studies have shown significantly worse performance (to non-diagnostic levels), see Thalassemia for references

Differential Diagnosis: Thalassemia

Study: Am J Clin Pathol. 2008 Mar;129(3):466-71. PMID: 18285271

Low Transferrin Saturation
Duplicate Edit
48%88%

<10%

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Sensitive Findings

Finding SensitivitySpecificity Comments, Study
Decreased Ferritin
Duplicate Edit
94%71%

<100ng/ml

Differential Diagnosis: Anemia of Chronic Disease

Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Poorly Diagnostic Findings

Finding SensitivitySpecificity Comments, Study
Paleness Edit 75%77%

i.e. a visual inspection of the patient, for Hct < 35%

Study: Acad Emerg Med. 2000 Feb;7(2):146-56. PMID: 10691073

Findings With Unspecified Accuracy

Finding SensitivitySpecificity Comments, Study
Trasferrin Receptor (soluble) Edit No accuracy specified.

An increased soluble transferrin receptor is helpful in diagnosing Iron Deficiency Anemia in a pt that also has Anemia of Chronic Disease.

Study: no study specified.

Increased Platelet Count Edit No accuracy specified.

Study: no study specified.