Pathology/Lab Coding Alert

Our experts decode IgG, IgM and more

When the test order looks like alphabet soup, selecting the proper CPT codes can be confusing. But if you know the antibody types and terminology, your job will be easier.

Understand Antibody Response

Humans produce different antibody isotypes in response to invading infectious organisms (antigens). Each isotype is an -immunoglobulin (Ig) class- that has different biological properties and functions.

Deciphering these Ig classes for a specific organism can help physicians learn about a patient's status. For instance, does the patient have a current infection, or has the patient had a past infection that conferred immunity?

Look at the following descriptions to understand how physicians might use these antibody isotypes:

- IgM -- These antibodies appear on the surface of B cells to help kill pathogens in the early stages of an infection. Physicians often look for rising IgM antibody levels over the course of a few weeks as an indication of acute infection, says William Dettwyler, MT-AMT, president of Codus Medicus, a laboratory coding consulting firm in Salem, Ore.

- IgG -- As an acute infection subsides, the body forms IgG antibodies that remain at a stable level for years to come, preparing the body to ward off any future assaults by the same organism. IgG antibodies can confer -immunity- against future infection.

- IgA -- This isotype occurs in mucous-containing body systems, such as the respiratory and urogenital tracts, to help prevent pathogens from colonizing those areas.

- IgE -- These antibodies are active in the body's allergic response and to protect against certain parasitic worms.

- IgD -- Also occurring on B cells, the function of IgD is less clear and has less clinical significance than other Ig classes.

What This Means to You

Understanding these antibody basics can help you select the proper CPT codes (one for each Ig class), as well as demonstrate medical necessity for repeat antibody testing. Keep in mind the following generalizations:

- IgG and IgM negative generally indicates no infection and no immunity.

- IgM positive (with rising values) and IgG negative indicates a current, acute infection.

- IgG positive and IgM negative indicates immunity. In these cases, the IgG class will often be the same as the total antibody measure.

- IgG and IgM positive indicate recent infection and immunity.