“A weak immune system” can mean many different things. It does not tell you which part of the immune system is affected, how serious the problem is or what care is appropriate. A useful explanation starts with a specific diagnosis.
Primary and secondary describe the cause
Primary immunodeficiencies, also called inborn errors of immunity, arise from problems intrinsic to the immune system. Some are recognised in childhood; others are diagnosed later. Secondary immunodeficiencies develop because of another condition or treatment, such as certain infections or immune-suppressing medicines.
The distinction does not rank severity. “Secondary” does not mean minor, and “primary” does not mean that everybody has the same risks. The Immune Deficiency Foundation’s terminology guide explains these terms.
Immune deficiency is different from autoimmunity
Immune deficiency involves inadequate immune protection. Autoimmunity involves an immune response directed against the body’s own tissues. They are different concepts, although some people experience both. An autoimmune diagnosis should not automatically be relabelled as immune deficiency.
The immune system has several interacting parts, including antibodies and different cells. Different disorders affect different functions. Read IDF’s explanation of how the immune system works for background.
There is more than one antibody deficiency
CVID and selective IgA deficiency are examples of distinct diagnoses, not interchangeable labels. Other conditions can affect different antibodies, immune cells or defence pathways. Treatment that helps one person may not be needed or suitable for another.
Our separate guides explain common variable immune deficiency (CVID) and selective IgA deficiency. Use them to prepare questions, not to assign yourself a diagnosis from symptoms or one blood result.
What happens during assessment?
Your medical history, examination and pattern of illness guide testing. Blood tests may assess different parts of immune function, and selected people need genetic investigations. The IDF diagnosis guide describes the approach. A clinician interprets results alongside the clinical history.
If you are concerned about repeated or unusually severe infections, bring a record of what actually happened. Dates, diagnoses, treatment and hospital visits are more useful than trying to remember everything under pressure. Include medicines that could affect immune function; do not stop them yourself.
Prepare a short record
- List infections, where they occurred and whether laboratory results are available.
- Record treatment, how well it worked and whether you needed hospital care.
- Bring previous blood results and a complete medicine list.
- Note family history and other symptoms you want to discuss.
- Write down your main question: diagnosis, treatment, prevention or follow-up.
Ask which findings remain uncertain and who will explain the next results. If you are referred, confirm where to go and what documents to bring. Our appointment guide can help.
Get an individual prevention and illness plan
Ask your clinician which symptoms need prompt contact and what to do out of hours. Severe breathing difficulty, collapse or new confusion needs emergency help, not a routine message. If you already have a specialist illness plan, follow it.
Vaccination advice depends on the condition and treatment. Check your own plan rather than assuming all vaccines are either suitable or unsuitable. See IDF’s vaccine information. Practical support with transport, appointments and daily tasks can be discussed through our Support Hub.
General health information, not an individual diagnosis or treatment plan. Sources checked on 16 September 2026. International sources may describe services or medicines that differ from those available in South Africa. The featured image is illustrative.
Prepare for the next assessment
- List important infections, hospital stays and unusual treatment responses with dates.
- Bring previous blood results and a full medicine list.
- Write down relevant family history without assuming relatives have the same condition.
- Ask which tests are needed and who will explain the results.
Keep a copy
Save the agreed plan and review date with your appointment notes. Our resources can help you find further information.
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