Anemia is the condition of a decrease in the number of circulating red blood cells (and therefore hemoglobin) below a normal range for the age and sex of the individual, which results in a decrease in the supply of oxygen to the tissues. . Iron deficiency anemia is a type of microcytic, hypochromic anemia, which is the most common nutritional disorder. Iron is an essential element in the synthesis of hemoglobin.
Iron deficiency anemia (IDA) can cause a problem in the differential diagnosis of other hypochromic anemias such as beta-thalassemia trait, alpha-thalassemia trait, HbE disease, sideroblastic anemia, or anemia due to chronic diseases. This topic will discuss laboratory investigations for IDA differential diagnosis of those conditions, along with some preliminary investigations.
1. Hemoglobin and Hematocrit
According to the WHO, the criteria for anemia is when adult men have hemoglobin levels <13 g / dL and adult women <12 g / dL. As iron deficiency worsens, both Hb and PCV decrease at the same time.
- Hb >12 g/dl : Not anemic
- Hb 10–11 g/dl : Mild anemia
- Hb 8–9 g/dl : Moderate anemia
- Hb 6–7 g/dl : Marked anemia
- Hb 4–5 g/dl : Severe anemia
- Hb < 4 g/dl : Critical
2. Red Cell Indices
MCV, MCH and MCHC are reduced. RDW is raised.
- Mean corpuscular volume (MCV): It is the mean volume of the RBC expressed in femtoliters. It becomes <80 fl in ADI (normal 82 to 98 fl).
- Mean corpuscular hemoglobin (MCH): MCH indicates the amount of hemoglobin (weight) per RBC and is expressed as picograms. MCH will be <25 pg in IDA (normal 27 to 32 pg).
- Mean Corpuscular Hemoglobin Concentration (MCHC): The MCHC measures the average concentration of hemoglobin in a red blood cell. MCHC drops below 27 g / dL (normal 31-36 g / dL).
- Red blood cell distribution width (RDW): RDW is a quantitative measure of anisocytosis. In IDA, RDW increases y> 15%. It is the first sign of iron deficiency (normal 11.5 to 14.5%).
Peripheral Blood Smear:
1. Red Blood Cells (RBCs):
- Microcytosis: Red blood cells are usually smaller than normal. The dimorphic blood picture is seen with a dual population of red blood cells, one of which is macrocytic and the other is microcytic and hypochromic when iron deficiency is associated with severe folate or vitamin B12 deficiency.
- Hypochromasia: central pallor in red blood cells is more than 1/3.
- Poikilocytosis – Elliptical shapes are common and elongated pencil (cigar) shaped cells can be seen. Target cells and teardrop cells may also be present in small numbers. Severe anemia shows ring / pessary cells.
2. White blood cells (WBC):
White blood cells are usually normal in number, but they can increase due to chronic stimulation of the spinal cord in cases of long duration. There may be associated eosinophilia if the iron deficiency is secondary to a hookworm infestation.
The platelet count is usually normal, but it can increase mildly to moderately, especially in patients who are bleeding.
4. Reticulocyte Count
The reticulocyte count is low in relation to the degree of anemia.
Bone Marrow Examination:
- Cellularity: moderately hypercellular.
- M: E ratio: ranges from 2: 1 to 1: 2 (normal 2: 1 to 4: 1).
- Erythropoiesis: hyperplasia and micronormoblastic maturation.
- Myelopoiesis: normal.
- Megakaryopoiesis: normal.
- Bone marrow iron: absent. “Gold standard” test, demonstrated by negative reaction to Prussian blue.
Serum iron profile studies are used to establish a differential diagnosis of hypochromic microcytic anemia.