Iron Deficiency Anemia: Likelihood Ratios

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

Prevalence

The likelihood ratios of findings for Iron Deficiency Anemia are listed below. See the left navigation bar to change the display.

Good Positive and Negative Likelihood Ratios

Finding	+LR	-LR	Comments, Study
Decreased Ferritin Duplicate	3.2	0.1	<100ng/ml Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Decreased Ferritin Duplicate	16	0.2	<35ng/ml Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Decreased Ferritin Duplicate	10.6	0.2	<45 ng/ml Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
RDW, increased Duplicate	7.5	0.2	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
Decreased Ferritin Duplicate	24.3	0.3	<25ng/ml Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Paleness	3.3	0.3	i.e. a visual inspection of the patient, for Hct < 35% Study: Acad Emerg Med. 2000 Feb;7(2):146-56. PMID: 10691073

Good Positive Likelihood Ratio

Finding	+LR	-LR	Comments, Study
Low Transferrin Saturation Duplicate	12	0.8	<5% Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Red Cell Protoporphyrin	7.8	0.7	>250mcg/dl Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
Decreased MCV	6	0.6	<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
Low Transferrin Saturation Duplicate	4	0.6	<10% Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761
RDW, increased Duplicate	2.6	0.9	>21 Differential Diagnosis: Anemia of Chronic Disease Study: J Gen Intern Med. 1992 Mar-Apr;7(2):145-53. PMID: 1487761

Findings With Unspecified Accuracy

Finding	+LR	-LR	Comments, Study
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.
Increased Platelet Count	No accuracy specified.		Study: no study specified.