Serum Immunofixation Test

Written by Darla Burke
Medically Reviewed by George Krucik, MD

What Is an Immunofixation-Serum Test?

Immunoglobulins (Ig) are also known as antibodies. These proteins protect the body against disease. There are many different types of Ig.

Certain diseases result in the growth of an excess number of antibody-producing cells. In some diseases these cells can produce a large amount of antibodies that are all exactly the same. These are called monoclonal antibodies. In a serum immunofixation (IFX) test, they appear as a spike called an M spike in this test. They are considered to be abnormal Ig.

In addition to detecting Ig, the IFX test can identify the type of abnormal Ig present. This information can be helpful in establishing a diagnosis.

Other common names for the test include:

  • immunofix by subtract
  • immunosubtraction, serum
  • kappa chains, serum
  • monoclonal protein study

Why Is the Test Ordered?

The IFX test is often used to diagnose multiple myeloma or Waldenstrom’s macroglobulinemia, when symptoms of the disorders are present. Both conditions produce abnormal Ig. Clinical symptoms of multiple myeloma include:

  • bone pain in the back or ribs
  • weakness and fatigue
  • weight loss
  • broken bones
  • recurrent infections
  • weakness in the legs
  • nausea/vomiting

Clinical symptoms of Waldenstrom’s macroglobulinemia include:

  • weakness
  • severe fatigue
  • bleeding from the nose or gums
  • weight loss
  • bruises or other skin lesions
  • blurred vision
  • swelling of the lymph nodes, spleen, or liver

This test alone cannot be used to make a diagnosis. The test only indicates whether abnormal Ig is present.

Another test must be used to measure the amount of abnormal Ig in the blood. This test is called serum protein electrophoresis test (SPET). It will be used by your doctor to confirm certain diagnoses.

The IFX test can also be used to study changes in the structure of normal proteins in the blood. One example is glucose-6-phosphate dehydrogenase. This protein enables red blood cells to function properly. Changes can lead to red blood cell problems. These changes can be detected through an IFX test.

How Is the Test Administered?

The IFX test is performed on a blood sample. The blood sample is taken from your arm by a nurse or lab technician. The blood will be collected in a tube and sent to a lab for analysis. Once the results are reported, your doctor will be able to explain your results.

Preparation for the Test

This test typically requires no preparation. However, in certain circumstances you may be asked to fast for 10 to 12 hours before the test. Fasting requires you to take no food or liquid, except water, by mouth.

What are the Risks of the Test?

Patients undergoing the IFX test may experience some discomfort when the blood sample is drawn. Needle sticks may result in pain or throbbing at the injection site during or after the test. Bruising may also occur.

The risks of the IFX test are minimal. These risks are common to most blood tests. Potential risks include:

  • difficulty obtaining a sample, resulting in multiple needle sticks
  • excessive bleeding at the needle site
  • fainting as a result of blood loss
  • accumulation of blood under the skin, known as a hematoma
  • development of infection at the puncture site

Understanding Your Test Results

A negative result indicates that no abnormal Ig is present. With a negative result, you may not need additional testing.

Positive results from the test indicate the presence of abnormal Ig. This may suggest the existence of an underlying health condition, such as:

  • an immune system disorder
  • multiple myeloma
  • Waldenstrom’s macroglobulinemia
  • other types of cancer

In some patients, positive results may not indicate an underlying problem. A small percentage of patients have low levels of monoclonal antibodies for no known reason. These patients do not develop any health problems. This condition is known as “monoclonal gammopathy of unknown significance” or MGUS.

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