# Primary Immunodeficiency Warning Signs

> Primary immunodeficiency warning signs for NEET-PG Paediatrics list the ten Jeffrey Modell signs and first screening tests by the part of immunity affected.

- Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/primary-immunodeficiency-warning-signs
- Exam / course: NEET-PG · Subject: Paediatrics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Nelson Textbook of Pediatrics; Ghai Essential Pediatrics; Jeffrey Modell Foundation Ten Warning Signs
- How to cite: "Primary Immunodeficiency Warning Signs", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/primary-immunodeficiency-warning-signs

## Direct answer

Primary immunodeficiency warning signs are recurrent, severe or unusual infections and related features that should prompt immune testing in a child. The Jeffrey Modell Foundation lists ten signs, including four or more ear infections within a year, two or more deep-seated infections and poor weight gain. Screening starts with a complete blood count and serum immunoglobulins, then moves to lymphocyte subsets and functional tests matched to the affected arm.

## What you must remember

- **Ear, sinus and chest:** four or more new ear infections, two or more serious sinus infections, or two or more pneumonias within a year.
- **Antibiotic response:** two or more months on antibiotics with little effect, or a need for intravenous antibiotics to clear an infection.
- **Growth and deep infection:** failure to gain weight or grow normally, recurrent deep skin or organ abscesses, and two or more deep-seated infections including septicaemia.
- **Thrush and family history:** persistent thrush in the mouth or fungal infection on the skin, and a family history of primary immunodeficiency.
- **Antibody defects:** the commonest group, with recurrent encapsulated bacteria such as pneumococcus and Haemophilus influenzae.
- **T cell defects:** opportunistic infections such as Pneumocystis, candida and viral infections, with chronic diarrhoea and failure to thrive.
- **Phagocyte defects:** catalase-positive bacteria and fungi, deep abscesses and poor pus formation.
- **Complement defects:** recurrent Neisseria meningitidis or encapsulated bacterial infections, sometimes with autoimmune disease.

## Choosing the test by the part of immunity affected

The infection pattern points to one arm of immunity, and the first test is chosen to match it. Total counts can look normal in antibody defects, so the test must target the specific arm.

| Part affected | Typical infection | First tests | Example |
|---|---|---|---|
| Antibody (B cell) | Pneumococcus, Haemophilus, Giardia | Serum IgG, IgA, IgM, vaccine titres | X-linked agammaglobulinaemia |
| T cell | Pneumocystis, candida, viral | Lymphocyte count, CD3 and CD4 subsets | Severe combined immunodeficiency |
| Phagocyte | Staphylococcus, Aspergillus, Serratia | Neutrophil count, DHR or NBT test | Chronic granulomatous disease |
| Complement | Neisseria, encapsulated bacteria | CH50, C3 and C4 | Terminal complement deficiency |

A child with two or more of the warning signs needs immunological evaluation, and a sibling or male cousin with the same problem strengthens the case. Screening should start with the complete blood count, immunoglobulins and vaccine responses before any specialised functional test is ordered. Infants under about six months may still carry maternal IgG, so low values are read with age in mind.

## Where the exam tests warning signs

Questions focus on the number of signs, the test matched to the immune arm and the safety of live vaccines.

- **Trap:** dismissing recurrent infections as bad luck and waiting for them to stop. — **Correct:** the Jeffrey Modell warning signs define when to test, and the infection pattern shows which immune arm to check.
- **Trap:** ordering only a complete blood count and calling immunity normal. — **Correct:** total counts can be normal in antibody defects, so immunoglobulins and vaccine responses are needed.
- **Trap:** giving live vaccines before the immune profile is known in a suspected T cell defect. — **Correct:** live vaccines are contraindicated in severe T cell defects, including BCG, until the diagnosis is excluded.

## Frequently asked questions

### How many warning signs suggest primary immunodeficiency?

The Jeffrey Modell Foundation lists ten warning signs for primary immunodeficiency. Two or more of these signs in a child suggest the need for immunological evaluation.

### Which first tests screen for primary immunodeficiency?

Screening starts with a complete blood count with differential and serum quantitative immunoglobulins IgG, IgA and IgM. Lymphocyte subsets and vaccine antibody responses are added next, with functional tests reserved for specific suspicions.

### Why are live vaccines dangerous in severe combined immunodeficiency?

Live vaccines can cause disseminated infection in severe combined immunodeficiency because the child cannot clear the attenuated organism. BCG is a notable example, so live vaccines are withheld until immune status is known.

### Does a family history add weight to primary immunodeficiency warning signs?

A family history of primary immunodeficiency, such as affected male relatives in an X-linked disorder, raises suspicion considerably. It is one of the ten warning signs and should prompt testing even when the child's own infections seem milder.