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How is IDA diagnosed?

Diagnosis

Gold standard

Traditionally, a definitive diagnosis requires a demonstration of depleted body iron stores by performing a bone marrow aspiration, with the marrow stained for iron. Because this is invasive and painful, while a clinical trial of iron supplementation is inexpensive and non-traumatic, patients are often treated based on clinical history and serum ferritin levels without a bone marrow biopsy.


Anemia may be diagnosed from symptoms and signs, but when anemia is mild it may not be diagnosed from mild non-specific symptoms.

Pica, an abnormal craving for dirt, ice, or other "odd" foods occurs variably in iron and zinc deficiency, but is neither sensitive or specific to the problem so is of little diagnostic help.

Anemia is often first shown by routine blood tests, which generally include a complete blood count (CBC) which is performed by an instrument which gives an output as a series of index numbers.

A sufficiently low hemoglobin (HGB) by definition makes the diagnosis of anemia, and a low hematocrit (HCT) value is also characteristic of anemia. If the anemia is due to iron deficiency, one of the first abnormal values to be noted on a CBC, as the body's iron stores begin to be depleted, will be a high red blood cell distribution width (RDW), reflecting an increased variability in the size of red blood cells (RBCs). In the course of slowly depleted iron status, an increasing RDW normally appears even before anemia appears.

A low mean corpuscular volume (abbreviated MCV) often appears next during the course of body iron depletion. It is the result of many red blood cells which are abnormally small.

A low MCV, a low mean corpuscular hemoglobin (MCH) and/or Mean corpuscular hemoglobin concentration (MCHC), and the appearance of the RBCs on visual examination of a peripheral blood smear narrows the problem to a microcytic anemia (literally, a "small red blood cell" anemia). The numerical values for red blood count, blood hemoglobin, MCV, MCH, MCHC are all calculated by modern laboratory equipment.

MCV (84-96 fL)       Hb (MCH) (26-36 pg)          MCHC (32-36%)

In Iron Anemia Hypochromic & Microcytic Anemia: MCHC less than 32% or an MCH under 27 % and MCV level below 80 fl

The blood smear of a patient with iron deficiency shows many hypochromic (pale and relatively colorless) and rather small RBCs, and may also show poikilocytosis (variation in shape) and anisocytosis (variation in size).

With more severe iron deficiency anemia the peripheral blood smear may show target cells, hypochromic pencil-shaped cells, and occasionally small numbers of nucleated red blood cells. Very commonly, the platelet count is slightly above the high limit of normal in iron deficiency anemia (this is mild thrombocytosis). This effect which was classically postulated to be to high erythropoietin levels in the body as a result of anemia, cross-reacting to activate thrombopoietin receptors in precursor cells which make platelets.

Body store iron deficiency is diagnosed by diagnostic tests as a low serum ferritin, a low Serum iron level, an elevated serum transferrin and a high total iron binding capacity (TIBC). A low serum ferritin is the most sensitive lab test for iron deficiency anemia, however, serum ferritin can be elevated by any type of chronic inflammation, and so is not Always a reliable test of iron status if it is within normal limits (i.e., this test is meaningful If abnormally low, but less meaningful if normal).

Change in lab values in iron deficiency anemia

Decrease      ferritin, hemoglobin, MCV

Increase         TIBC, transferrin, RDW 

WHO's Hemoglobin thresholds used to define anemia (1 g/dL = 0.6206 mmol/L):

A reticulocyte count is a quantitative measure of the bone marrow's production of new red blood cells. The reticulocyte production index is a calculation of the ratio between the level of anemia and the extent to which the reticulocyte count has risen in response. If the degree of anemia is significant, even a "normal" reticulocyte count actually may reflect an inadequate response. If an automated count is not available, a reticulocyte count can be done manually following special staining of the blood film.

In manual examination, activity of the bone marrow can also be gauged qualitatively by subtle changes in the numbers and the morphology of young RBCs by examination under a microscope. Newly formed RBCs are usually slightly larger than older RBCs and show polychromasia. Even where the source of blood loss is obvious, evaluation of erythropoiesis can help assess whether the bone marrow will be able to compensate for the loss, and at what rate. When the cause is not obvious, clinicians use other tests: ESR, ferritin, serum iron, transferrin, RBC folate level, serum vitamin B12, hemoglobin electrophoresis, renal function tests (e.g. serum creatinine).

When the diagnosis remains difficult, a bone marrow examination allows direct examination of the precursors to red cells.