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SERUM IRON TESTING
When is serum iron testing indicated?
Serum iron tests are indicated when the results from a complete blood count (CBC)
indicate that your pet is anemic (decreased red blood cell numbers and decreased
hemoglobin) and that the red blood cells are microcytic (smaller than usual) and
hypochromic (contain less hemoglobin than usual).
Why do these changes suggest iron
deficiency?
Microcytic red blood cells are suggestive of iron
deficiency because iron is needed for the
production of hemoglobin. With less iron
available, less hemoglobin is made and the
maturation sequence of red blood cells in the
bone marrow is affected, resulting in smaller red
blood cells that contain less hemoglobin.
What causes iron deficiency anemia?
Anemia may also be assessed by
evaluating the color of the gums and other
mucous membranes.
Because blood is a rich source of iron, chronic
external blood loss can lead to iron deficiency anemia. Causes of chronic blood loss
include large burdens of intestinal parasites such as hookworms, and external parasites
such as fleas. Chronic blood loss from the gastrointestinal tract or from the urinary tract
may also lead to iron deficiency anemia.
Young animals on a predominantly milk based
diet may also experience a transient, mild iron
deficiency anemia because milk is a poor
source of iron. This condition does not usually
require treatment in puppies and kittens that
are otherwise healthy.
What specific blood tests are available
to document iron deficiency anemia?
Severe flea and/or hookworm parasite
infestations can cause chronic blood loss
and iron deficiency anemia
These tests require a single blood sample that
is sent to a veterinary referral laboratory.
The amount of iron in serum can be
determined. With iron deficiency, the serum
iron concentration is expected to be low. However, serum iron can also be low with
other illnesses, so this finding is not specific for iron deficiency anemia.
The total iron binding capacity (TIBC) of a serum sample can be determined. The
TIBC does not specifically measure iron concentration, but rather measures the total
amount of transferrin (a blood protein that transports iron) that is available for binding to
and transporting iron. In many species, transferrin concentrations are increased in iron
deficiency anemia. Although transferring concentrations are not increased in iron
deficiency anemia in the dog, TIBC measurement is still useful in the dog because by
measuring the serum iron concentration and the TIBC, we can determine the %
transferrin saturation.
The % transferrin saturation is essentially the amount of the iron transport protein that is
currently being occupied by iron. The amount of binding or % saturation is decreased in
iron deficiency anemia.
Serum ferritin determination can also be used to assess the iron status. Ferritin is a
storage form of iron. A small amount of ferritin is found in the circulation. The circulating
form is thought to be a good indicator of total body iron stores. Until recently, serum
ferritin concentrations were available only for research purposes but certain referral
laboratories are now offering this test.
Another, less commonly used method of evaluating iron deficiency anemia is the
measurement of erythrocyte protoporphyrin. Protoporphyrins are intermediate
compounds formed during hemoglobin production. Protoporphyrin concentrations
increase with iron deficiency.
The most accurate,), but most invasive, method of assessing iron stores is to look
at the bone marrow (except in the cat).
This requires that a sample of the marrow be taken
using a special bone marrow needle. The bone
marrow sample can then be spread onto glass
slides, or if a piece of marrow tissue is obtained,
then sections of this material can be examined.
Both methods require that the samples be
submitted to a referral laboratory where a
veterinary pathologist examines both the stages of
red blood cells present in the sample and the
amount of stored iron. In order to accurately assess
the amount of iron present in a sample, special
stains are used to highlight the iron stores.Little to
no stainable iron is found in animals with iron
deficiency.
Why may bone marrow evaluation not be useful in the cat?
Even healthy cats do not have an appreciable amount of stainable iron stores in their
bone marrow. However, the pattern of red blood cell development in a bone marrow
sample may still be useful in evaluating the possible cause of an anemia.
What tests can be done to try to determine the cause of the anemia?
A serum biochemistry profile, urinalysis, and fecal evaluation are often used as
screening tests to try to determine the cause or source of the chronic blood loss.
The biochemistry profile may indicate low serum proteins; this finding confirms an
external loss of blood. The biochemistry profile may indicate that there is ongoing
intestinal bleeding by an elevation in a substance called urea.
A urinalysis (urine sample) can be evaluated for the presence of red blood cells. As
well, an examination of the cellular components of a urine sample (termed urine
sediment examination) may alert us to the presence of unusual cells that might
suggest an underlying bladder tumor as the source of the blood loss.
A fecal sample can be analyzed for the presence of intestinal parasites that may be
contributing to blood loss via the gastrointestinal tract.
Depending upon what is found with these screening tests, further diagnostic testing may
be required to pinpoint the source of chronic blood loss.
This client information sheet is based on material written by Kristiina Ruotsalo, DVM, DVSc, Dip ACVP &
Margo S. Tant BSc, DVM, DVSc.
© Copyright 2004 Lifelearn Inc. Used with permission under license. February 12, 2016