Skip to main content
IDF logo
DNA helix illustration.

Specific antibody deficiency

Individuals with specific antibody deficiency have normal levels of antibodies (immunoglobulins) but cannot produce antibodies to specific types of microorganisms that cause respiratory infections.


Among the five classes of immunoglobulins, IgG has the biggest role in protecting against infection. Some people have normal levels of immunoglobulins and all subclasses of IgG, but they do not produce sufficient specific IgG antibodies to protect them from some viruses and bacteria. People who produce normal immunoglobulin levels but who cannot produce protective IgG antibodies against the types of organisms that cause upper and lower respiratory infections have specific antibody deficiency (SAD). SAD is sometimes termed partial antibody deficiency or impaired polysaccharide responsiveness.

Each individual IgG molecule is uniquely designed to protect against a specific pathogen. We call these molecules specific antibodies, and they are usually formed in response to natural exposure to bacteria and viruses, or through exposure to vaccines. Some of these antibodies can be measured in the laboratory, and these levels (or titers) are used to help diagnose problems with immunity.

Children less than 2 years of age often do not have a robust response to bacterial infections such as Streptococcus pneumoniae, Moraxella catarrhalis, or Haemophilus influenzae. This is primarily due to an inability to make antibodies against the polysaccharide (sugar) coat that covers these bacteria. Children in this age group typically acquire protection against these microbes through the use of certain vaccines in which a protein is added to provoke an immunologic response (conjugate vaccines).

Most children begin to naturally make stronger immune responses to these bacteria around 2 years of age, and they can then fight off these infections more effectively. Children and adults who fail to develop the antibody response to the polysaccharide coating on bacteria (and therefore lack protection against these microbes) but who otherwise have normal antibody levels are diagnosed with SAD.

Specific IgG antibodies are important in fighting off infections; however, other components of our immune system also work to eradicate bacteria and viruses. T cells, complement proteins, IgM and IgA antibodies (to name a few) are parts of our immune system that work together during a complete immune response. If these other components work well, some individuals with low specific antibody levels may rarely get sick. 

Antibodies of certain IgG subclasses interact readily with the complement system, while others interact poorly, if at all, with the complement proteins. Thus, an inability to produce antibodies of a specific subclass or mild deficiencies of other arms of the immune system may render the individual susceptible to certain kinds of infections but not others. These factors must be taken into account before an individual's immune system is considered to be abnormal, either by virtue of having a low IgG subclass level or an inability to make a specific type of antibody.

Find specific antibody deficiency clinical trials

See if you qualify to participate in clinical trials evaluating new treatments and/or diagnostics for specific antibody deficiency.

Clinical presentation

Recurrent ear infections, sinusitis, bronchitis, and pneumonia are the most frequently observed illnesses in people with SAD. Some individuals show an increased frequency of infection beginning in the first years of life. In others, the onset of infections may occur later. In general, the infections in individuals with SAD are not as severe as those who have combined deficiencies of IgG, IgA, and IgM, like X-linked agammaglobulinemia (XLA) or common variable immune deficiency (CVID). Some, however, may present with a single severe pneumonia or other infection at the time of diagnosis.


Problems with specific antibody production may be suspected in children and adults who have a history of recurrent infections of the ears, sinuses, bronchi, and/or lungs. The recommended evaluation usually includes measurement of total immunoglobulins, and antibody levels to specific bacteria such as tetanus, diphtheria, and/or Streptococcus pneumoniae.

When total immunoglobulins are low, a more profound immunodeficiency may be present. If isolated low antibody levels to Streptococcus pneumoniae are found during the initial evaluation, a pneumococcal vaccine (Pneumovax) is administered and follow-up levels are measured. Individuals older than 1 year of age may be immunized with the pneumococcal polysaccharide vaccine (Pneumovax 23 or Pnuimmune 23). These vaccines have the ability to induce protective antibody levels to 23 strains (serotypes) of Streptococcus pneumoniae. Antibody levels are measured again 4-6 weeks later to determine if adequate protective antibody levels were produced. Individuals without PI respond to a majority of the serotypes in these vaccines and retain those protective levels for years after receiving them. Antibody responses may not last as long in young children.

For therapy, it is also possible to re-immunize with Prevnar 13, a conjugate type of pneumococcal vaccine, which, for most, may be more immunogenic than Pneumovax. This vaccine, however, cannot be used to diagnose SAD.

A classification for mild, moderate, and severe forms of SAD exists that factors in the individual's age and number of normal post-immunization serotypes to define immunologic severity. Responses in which children respond to <50% of serotypes and adults respond to <70% have a moderate form of SAD with an increased risk of upper/lower respiratory tract infections that may warrant treatment. In the experience of many clinical immunologists, however, a normal vaccine response for an individual consists of producing protective titers of antibodies to at least 50% of the serotypes present in the vaccine. Furthermore, there are individuals who may fall into a response zone between 50-70% that have significant infections that may warrant a trial of immunoglobulin (Ig) replacement therapy.

An additional subset of people have a memory phenotype, meaning they respond normally initially and subsequently lose protective levels within six months.

When interpreting pneumococcal levels, it is important to recognize the variability in testing methodology and subsequent results that may occur among different labs. This highlights the importance of using a detailed clinical history in addition to laboratory findings to guide the immunologic evaluation when considering a diagnosis of SAD.


No clear-cut pattern of inheritance has been observed with SAD.


Individuals with SAD frequently have recurrent or chronic infections of the ears, sinuses, bronchi and lungs. Treatment of these infections usually requires antibiotics. One goal of treatment is to prevent permanent damage to the ears and lungs that might result in hearing loss or chronic lung disease with scarring. Another goal is to maintain individuals with SAD as symptom-free as possible so that they may pursue the activities of daily living such as school or work. Sometimes, antibiotics may be used for prevention (prophylaxis) of infections.

As in IgG subclass deficiency, the use of Ig replacement therapy for SAD is not as clear-cut as it is for those with X-linked agammaglobulinemia (XLA) or common variable immune deficiency (CVID). For individuals with SAD in whom infections and symptoms can be controlled with antibiotics, Ig replacement therapy is usually not necessary. However, for those with more severe clinical phenotypes whose infections cannot be readily controlled with antibiotics or who have more frequent and severe infections, Ig replacement therapy may be considered.

Since many young children appear to outgrow SAD as they get older, it is important to reevaluate them to determine if the deficiency is still present. If Ig replacement therapy has been previously initiated, reevaluation after a period of time is recommended, with discontinuation of Ig therapy for 4-6 months before repeat immune testing and re-immunization with pneumococcal vaccines (if needed) is performed. If the response to vaccination is adequate, Ig replacement therapy may be discontinued and the individual observed. It is reasonable to reevaluate antibody levels periodically to document the retention of protective antibody levels. If the diagnosis of SAD is made in teenagers or adults, resolution of the deficiency is less likely.


The outlook for individuals with SAD is generally good. Many children appear to outgrow their deficiency as they get older, usually by age 6. For those for whom the deficiency persists, the use of prophylactic antibiotics and, in certain circumstances, the use of Ig therapy may prevent serious infections and the development of impaired lung function, hearing loss, or injury to other organ systems.

The natural history of individuals with SAD is not completely understood. SAD seems to occur more often in children, probably due to a delay in the natural maturation of the immune response. Children may outgrow SAD over time.

Adults with similar symptoms and poor response to vaccination are less likely to improve over time. Similar to IgG subclass deficiencies, SAD may evolve into CVID. At the present time, it is not possible to determine which individuals will have the transient type of deficiency as opposed to permanent deficiency, or which individuals will progress to a more wide-ranging immunodeficiency, such as CVID. For these reasons, periodic reevaluation of immunoglobulin levels and specific antibody levels is necessary.

This page contains general medical and/or legal information that cannot be applied safely to any individual case. Medical and/or legal knowledge and practice can change rapidly. Therefore, this page should not be used as a substitute for professional medical and/or legal advice.

Adapted from the IDF Patient & Family Handbook for Primary Immunodeficiency Diseases, Sixth Edition 
Copyright ©2019 by Immune Deficiency Foundation, USA