From the Guidelines
Anemia is diagnosed as a hemoglobin (Hb) concentration below the lower limit of normal for the relevant population and laboratory performing the test.
Diagnosis Criteria
The diagnosis of anemia can be made based on the following criteria:
- Hemoglobin (Hb) concentration below the lower limit of normal for the relevant population and laboratory performing the test 1
- Hematocrit (Hct) can also be used to screen for iron deficiency, but it is a late indicator of iron deficiency and only falls after the Hb concentration falls 1
Anemia Classification
Anemia can be classified into different types based on the mean corpuscular volume (MCV) or average RBC size:
- Microcytic (< 80 fL): most commonly caused by iron deficiency
- Normocytic (80–100 fL): may be caused by hemorrhage, hemolysis, bone marrow failure, anemia of chronic inflammation, or renal insufficiency
- Macrocytic (> 100 fL): most is megaloblastic, indicating vitamin B12 or folate deficiency caused by insufficient uptake or inadequate absorption through lack of intrinsic factor 1
Diagnostic Tests
The following tests can be used to diagnose and differentiate anemia:
- Complete blood count (CBC) to determine Hb concentration, Hct, and MCV
- Reticulocyte count to determine the underlying mechanism of anemia
- Serum ferritin concentration to diagnose iron deficiency
- Transferrin saturation and total iron binding capacity (TIBC) to diagnose absolute iron deficiency 1
Threshold Values
The following threshold values can be used to diagnose anemia:
- Hb < 135 g/L in males ≥ 18 years of age
- Hb < 120 g/L in females ≥ 18 years of age 1
From the Research
Diagnosis of Anemia
The diagnosis of anemia is typically based on a low red blood cell count, a low hematocrit, or a low hemoglobin concentration 2, 3, 4.
- A hemoglobin concentration of less than 11.0 g/dL in the first trimester and less than 10.5 or 11.0 g/dL in the second or third trimester is considered anemia in pregnancy 2.
- Anemia can be classified into different types, including microcytic, normocytic, and macrocytic anemias, based on the size of the red blood cells 4.
- The diagnosis of anemia of chronic diseases is based on a complex process, usually initiated by cellular immunity mechanisms and pro-inflammatory cytokines and hepcidin, and is characterized by a decrease in hemoglobin, hematocrit, and erythrocyte counts 5.
Diagnostic Tests
The following diagnostic tests are used to evaluate anemia:
- Complete blood count (CBC) with red cell indices 2, 6
- Reticulocyte count to screen for hemolysis or blood loss 6
- Testing for specific causes of anemia, such as iron deficiency or vitamin B12 deficiency 2, 5, 6
- Examination of the bone marrow may be required for diagnosis in some cases 6
- Molecular testing is increasingly being used to aid in the diagnostic process 6
Evaluation of Anemia
A detailed history and physical examination, along with laboratory test results, can help detect the correct cause of anemia in most patients 4, 6.
- The evaluation of microcytic anemia, for example, involves a detailed history and physical examination, as well as laboratory tests such as a CBC and iron studies 4.
- The American College of Obstetricians and Gynecologists recommends screening for anemia with a complete blood count in the first trimester and again at 24 0/7 to 28 6/7 weeks of gestation 2.