microsomal antibody test is also called a thyroid peroxidase test. It measures
antithyroid microsomal antibodies in your blood. Your body produces these
antibodies when cells in your thyroid become damaged. Your thyroid is a gland in your neck
that makes hormones. These hormones help regulate your metabolism.
Your doctor may order this test along with other tests to
help diagnose thyroid problems or other autoimmune conditions.
How Your Blood Is Drawn
A blood draw is a simple procedure that has few risks.
Actual testing of your blood takes place in a laboratory. Your doctor will
discuss the results with you.
Be sure to inform your doctor about all the prescription and
over-the-counter medications and supplements you take. Your doctor may instruct
you to stop eating and drinking for six to eight hours before this test. This
is called fasting. If you fast before a test, you may get more accurate
Your healthcare provider will choose a site on your arm,
typically the back of your hand or the inside of your elbow, and clean it with
antiseptic. An elastic band is then tightened around your upper arm to make
your veins swell. This will make it easier to access the vein.
A needle will be inserted into your vein. You may feel a
stinging or pricking sensation as the needle is inserted. Some people report
mild throbbing or discomfort. A small amount of blood will then be collected
into a tube. Once the tube is filled, the needle will be removed. A bandage is
usually placed over the puncture site.
For babies or young children, a sharp tool called a lancet
is sometimes used for the skin puncture and the blood is collected onto a
The blood sample is sent to a laboratory for analysis. Your
doctor will discuss your results with you.
Risks and Side Effects
There are few risks or side effects associated with a blood
test. Veins vary in size. Your healthcare provider may occasionally have difficulty
obtaining the sample.
Any time your skin is broken, there’s a slight risk of
infection. You should notify your doctor right away if the area of the blood
draw swells or starts to produce pus.
Other minimal risks include:
What the Results Mean
Blood test results are processed within a week. In some
cases, doctors receive them within a few days. Your doctor will explain your
specific results to you. A test that comes back as negative for antithyroid
microsomal antibodies is considered a normal result. These antibodies are
usually not found in a healthy immune system.
If you have an autoimmune disease or thyroid disorder, your
antibody levels may rise. A positive test indicates an abnormal result and may
be due to a variety of conditions, including:
thyroiditis, which is a swelling of the thyroid gland that often results
in reduced thyroid function
disease, which is an autoimmune disorder in which the thyroid gland is
thyroiditis, or subacute thyroiditis, which is a swelling of the thyroid
gland that usually follows an upper respiratory infection
hemolytic anemia, which is a drop in the number of red blood cells due to
increased destruction by the immune system
nodular goiter, which is an enlargement of the thyroid gland with cysts
syndrome, which is an autoimmune disorder in which the glands that produce
tears and saliva are damaged
lupus erythematosus, which is a long-term autoimmune disorder affecting
your skin, joints, kidneys, brain, and other organs
Women with high levels of antithyroid microsomal antibodies
have a higher risk of:
- premature birth
- difficulty with in vitro fertilization
Having antithyroid antibodies in your blood doesn’t automatically
mean you have a thyroid disease. However, you may be at increased risk for
future thyroid disease, and your doctor may want to monitor your condition. For
unknown reasons, the risk tends to be higher in women.
There’s also the possibility of false-positive and false-negative
results. False positives from this test usually indicate a temporary increase
in antithyroid antibodies. False-negative results mean that your blood test
doesn’t reveal the presence of the antibodies when they’re actually there. You
can also get a false negative if you didn’t fast or you’re on certain
medications. Therefore, it’s important to follow all of your doctor’s orders
when taking the blood test.
Your doctor will perform further diagnostic tests if
antithyroid microsomal antibodies are found. These antibodies usually indicate
an autoimmune disease. Other thyroid issues such as hypothyroidism will
probably be ruled out from the start if you have these antibodies present. Your
doctor may order an ultrasound, biopsy, and radioactive iodine test to narrow
down your diagnosis. You’ll probably need blood testing every few months until
your condition is under control.