Diagnostic Approach for Anemia with Normal Red Cell Indices

Initial Assessment

The World Health Organization criteria for anemia are: hemoglobin <130 g/L in men, <120 g/L in non-pregnant women, and <110 g/L in pregnant women, according to the American College of Gastroenterology 1, 2
Normal MCH, MCHC, and RDW with anemia suggests normocytic anemia, which can indicate anemia of chronic disease, early iron deficiency, acute blood loss, or bone marrow disorders, as stated by the National Comprehensive Cancer Network 1, 3

Serum ferritin is the single most useful marker for iron deficiency, with a level <15 μg/L being highly specific for iron deficiency, and <30 μg/L indicative of low body iron stores in the absence of inflammation, according to the European Crohn’s and Colitis Organisation 1, 2, 4
Transferrin saturation values <15-16% suggest iron deficiency, as recommended by the American Gastroenterological Association 1, 2
C-reactive protein (CRP) is essential to assess for underlying inflammation that may affect ferritin interpretation, as stated by the National Institute for Health and Care Excellence 1, 2
Reticulocyte count is critical to assess bone marrow response, with low or normal reticulocytes suggesting impaired erythropoiesis, and high reticulocytes suggesting blood loss or hemolysis, according to the American Society of Clinical Oncology 3, 6

If iron deficiency is suspected, additional tests include total iron-binding capacity (TIBC), serum iron, and stool guaiac test to assess for occult GI bleeding, as recommended by the National Comprehensive Cancer Network 1, 3, 6
If hemolysis is suspected, additional tests include haptoglobin, lactate dehydrogenase, and indirect bilirubin, as stated by the American Society of Hematology 6
If macrocytosis develops or is masked by microcytosis, additional tests include vitamin B12 and folate levels, and hemoglobin electrophoresis if thalassemia is suspected, according to the American College of Medical Genetics and Genomics 1, 2

A therapeutic trial of iron supplementation can be diagnostic, and a good response to iron therapy strongly suggests iron deficiency, even with equivocal iron studies, as recommended by the European Crohn’s and Colitis Organisation 4, 5

Relying solely on MCV, MCH, and RDW can be misleading, as these parameters may be normal in early iron deficiency or mixed deficiency states, as stated by the National Institute for Health and Care Excellence 1, 2
Misinterpreting ferritin in inflammatory states can lead to incorrect diagnosis, as inflammation can elevate ferritin despite iron deficiency, according to the American College of Rheumatology 1, 2
Overlooking mixed deficiency states can lead to incorrect diagnosis, as concurrent B12/folate deficiency can mask microcytosis of iron deficiency, as stated by the National Comprehensive Cancer Network 2
Failing to consider anemia of chronic disease can lead to incorrect diagnosis, as this is a common cause of normocytic anemia with normal red cell indices, according to the American Society of Clinical Oncology 2, 3