Immunoglobulin G (IgG) is a blood plasma component that is essential to healthy immune system functioning. IgG helps neutralize bacteria, viruses, and environmental toxins before they can infect and damage body cells. An IgG deficiency can leave a person susceptible to chronic and recurring infections, especially respiratory infections such as bronchitis and pneumonia. Most patients who have the condition need to take antibiotics on a regular basis and schedule frequent checkups with their doctors to prevent serious complications. In the case of a severe IgG deficiency, periodic blood transfusions may be necessary to replenish IgG levels throughout the patient's life.

Several different factors can contribute to an IgG deficiency, but most cases are associated with inherited genetic disorders. X-linked agammaglobulinemia, a condition that primarily affects males, inhibits the development of IgG-creating B cells in the immune system. Genetic conditions tend to become prevalent in infancy or very early childhood. A person can also develop an IgG deficiency later in life due to protein malnutrition, kidney failure, or cancer. In addition, long-term use of anticonvulsants and immunosuppressive drugs for other conditions has been linked with diminished IgG levels.

An IgG deficiency itself does not normally cause physical symptoms, but it can leave the body highly vulnerable to frequent viral and bacterial infections. A person with an IgG deficiency is likely to experience recurring respiratory infections that can cause bronchitis, pneumonia, and obstructive lung disease. Chronic sinus infections, influenza, and bacteria-related skin infections are also common with IgG deficiencies. Severely low levels of IgG can also render vaccines useless, and vaccinations may actually trigger the illnesses they are designed to prevent.

A doctor usually decides to screen for IgG deficiency and other immune system disorders when a patient suffers from chronic infections. Blood samples are taken and analyzed in a hospital lab to measure IgG levels. If a patient has severe recurring respiratory problems, a computerized tomography scan may be performed to gauge the physical damage to the lungs.

Some patients do not need to receive treatment directly targeted at their deficiencies. If IgG levels are moderately low, daily antibiotics and regular visits to the doctor's office may be sufficient. IgG replacement therapy, which involves transfusions every three to four weeks, may be needed if levels are very low. Surgery is not effective at improving a deficiency, but a procedure may be needed if infections have seriously damaged lung or sinus tissue. Most patients are able to manage their conditions when they take preventive measures against infections and follow their doctors' orders.