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.