What is Immunofixation?

Immunofixation is a lab test a doctor can order to look for the presence of particular proteins in a blood or urine sample. Sometimes, the goal is diagnostic, to learn more about a medical problem, and in other cases a doctor may order the test to assess a patient's response to treatment or monitor an ongoing medical issue. The immunofixation test can check for signs of cancers and certain diseases, and requires around three hours of lab time.

In this test, a technician takes a sample and subjects it to electrophoresis, where a current runs through a gel matrix with the sample. The current forces proteins in the sample to organize themselves by size, grouping like with like. The technician will add antigens to the gel. If the antigens find antibodies to react to, they create a dark stripe. The stripe indicates a positive test, showing antibodies of concern in the sample. The technician will write up the results for the doctor.

The immunofixation test is very useful for looking for monoclonal immunoglobulins. These arise when numerous clones of a parent cell are all producing identical immunoglobulins, as seen in patients with conditions like myeloma. A positive result does not necessarily mean a patient has cancer or another disease associated with monoclonal immunoglobulins, but it can certainly be an indicator of the need for further diagnostic testing to determine the cause.

One advantage of immunofixation is relative rapidity, when compared with other available tests. It can also be more sensitive. In a hospital with its own lab facilities, it may be possible to turn results around very quickly, unless the lab has a heavy work load. Patients with concerns about how long they need to wait for test results can ask their doctors about what to expect.

As with other lab tests, positive and negative results on an immunofixation test are not necessarily definitive. Many factors can lead to false results and a doctor may want another test to follow up. It is also possible to have an ambiguous result, where there is not enough information available to draw any firm conclusions about the patient's case. A doctor may ask to repeat the test and see if it is possible to get better results, or may recommend a different test. Test results alone are not enough to start treatment; the doctor also needs to consider any findings from the patient's examination.