What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Taking certain medicines. Be sure your doctor knows all of the medicines you take. Some medicines that affect test results include ones used for birth control, heart failure, seizures, and rheumatoid arthritis.
• Having cancer treatments, both radiation and chemotherapy.
• Receiving a blood transfusion in the past 6 months.
• Getting vaccinations (immunizations), especially vaccinations with repeat (booster) doses, in the past 6 months.
• Using alcohol or illegal drugs.
• Having a radioactive scan in the past 3 days.

What To Think About

• Immunoglobulins are made specific to different illnesses. For example, the IgM antibody for mononucleosis is different than the IgM for herpes. For this reason, a doctor can look for an immunoglobulin to a specific illness to help diagnose that illness.
• Different antibodies can be used to help a doctor tell the difference between a new and past infection. For example, IgM antibodies for mononucleosis with or without IgG antibodies means a new mono infection. IgG antibodies without IgM means a past mono infection.
• People with very low immunoglobulin levels, especially IgA, IgG, and IgM, have a higher chance of developing an infection.
• A very small number of people cannot make IgA and have a higher chance of developing a potentially life-threatening reaction to a blood transfusion.
• An immunoglobulin test is often done when the results of a blood protein electrophoresis or total blood protein test are abnormal. For more information, see the topics Serum Protein Electrophoresis (SPEP) and Total Serum Protein.