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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Differential Diagnoses include: Anemia of Chronic Disease, Thalassemia

Prevalence

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

Anemia of Chronic Disease

Finding	Sensitivity	Specificity	Comments, Study
Decreased Ferritin Duplicate	73%	97%	<25ng/ml Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Decreased Ferritin Duplicate	80%	95%	<35ng/ml Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Decreased Ferritin Duplicate	85%	92%	<45 ng/ml Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Decreased Ferritin Duplicate	94%	71%	<100ng/ml Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Decreased MCV	42%	93%	<75um^3. FYI, for <80um^3 (usual lower limit of normal) sens = 54%, spec = 81%. Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Low Transferrin Saturation Duplicate	24%	98%	<5% Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Low Transferrin Saturation Duplicate	48%	88%	<10% Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
RDW, increased Duplicate	13%	95%	>21 Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Red Cell Protoporphyrin	31%	96%	>250mcg/dl Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Thalassemia

Finding	Sensitivity	Specificity	Comments, Study
RDW, increased Duplicate	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 Study: Am J Clin Pathol. 2008 Mar;129(3):466-71. PMID: 18285271

Untagged

Finding	Sensitivity	Specificity	Comments, Study
Increased Platelet Count	No accuracy specified.		Study: no study specified.
Paleness	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
Trasferrin Receptor (soluble)	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.