Genetic testing for pediatric immune disorders: pre-test checklist

The same variant may matter very differently in a child with absent B cells, recurrent viral infections, or a family history of early deaths. Genetic testing preparation for pediatric immune disorders therefore begins before a sample is collected: with a clear immune phenotype, a useful family history, and an honest discussion of what the test can—and cannot—answer.

The aim is not to make every case fit a molecular diagnosis. It is to give the laboratory enough relevant information to interpret findings responsibly, while choosing an assay that matches the clinical question.

Establishing the Clinical Baseline Before Molecular Testing

Molecular testing is most useful when it follows a defined clinical and immunological assessment. The exact workup depends on the child’s symptoms and the questions raised by the treating specialist, but quantitative immunoglobulins and lymphocyte phenotyping often provide an essential starting point.

• Serum immunoglobulins: IgG, IgA, and IgM—and IgE when clinically relevant—help describe the humoral immune compartment. A pattern of low or absent immunoglobulins may direct attention toward particular pathways or genes, but results must be interpreted in light of age, treatment, and clinical history.
• Lymphocyte subsets: Flow cytometry can measure the number and proportion of T cells, B cells, and natural killer (NK) cells. A pattern such as low or absent T cells, or a marked reduction in B cells, can help narrow the differential diagnosis and guide assay selection.
• Newborn screening results: If available, records of T-cell receptor excision circle (TREC) or kappa-deleting recombination excision circle (KREC) screening may add useful context about early T- or B-cell development. The immunologist should interpret these results alongside subsequent tests and treatments rather than treating them as a substitute for a current assessment.

Clinical documentation for pediatric genetic screening should make the phenotype legible to someone who has not met the child. Include the age at symptom onset, infection types and severity, unusual or persistent infections, relevant laboratory findings, and major treatments. A short, specific summary is more useful than a generic indication such as “immune problem.”

Family history: more than a list of diagnoses

Gathering family medical history for genetic testing means asking about patterns, not only confirmed diagnoses. Early deaths, recurrent severe infections, autoimmune disease, unexplained cytopenias, lymphoproliferation, and granulomatous disease may all be relevant, even when relatives were never given a formal immune diagnosis.

Record which relatives are affected and how they are related to the child. Ask about both sides of the family, and note consanguinity when applicable. A history of affected boys connected through the maternal line, for example, may raise a different set of questions from a pattern affecting several siblings of different sexes.

If the testing strategy may include parental samples, establish whether those samples are available and whether the parents are willing to participate. Trio testing can help clarify whether a finding is inherited or arose de novo, but it does not replace careful clinical interpretation.

A sequence result needs a clinical frame. The immune phenotype and family history are part of the evidence, not paperwork added after the test.

Navigating Vaccine Safety and Immunological Contraindications

Vaccine history belongs in both the clinical assessment and the laboratory request. In a child with suspected severe T-cell deficiency, SCID, or combined immunodeficiency, live vaccines require particular care. Decisions about vaccination should be made with the child’s clinical team; a general checklist cannot determine whether an individual child should receive a vaccine.

The immunologist should review whether the child has received, or is scheduled to receive, live-attenuated vaccines. Depending on the child’s history and local immunization program, this may include MMR, rotavirus, varicella, BCG, oral polio vaccine, yellow fever, or live-attenuated influenza vaccine. Record the vaccine and timing as accurately as possible.

The concern in significant cellular immune deficiency is that a live vaccine may cause infection rather than the intended limited immune exposure. If SCID or another serious T-cell defect is suspected, seek specialist guidance before a live vaccine is administered. If a child has already received one, that history should prompt timely clinical review; it should not be reduced to a note on a requisition.

Vaccine history can also matter when interpreting later investigations. For example, detection of vaccine-strain rotavirus in stool may complicate the assessment of prolonged diarrhea after vaccination. The relevance depends on the clinical question and timing, so the laboratory and clinician need the context rather than a bare yes-or-no vaccination field.

Pre-test counseling for childhood immunodeficiency should make clear that genetic testing is not a substitute for urgent clinical management. When a child’s presentation raises concern for severe immune dysfunction, decisions about precautions, infection evaluation, and referral should proceed on clinical grounds while molecular testing is arranged.

Selecting Diagnostic Modalities: From Targeted Panels to WGS

A targeted panel, whole-exome sequencing (WES), and whole-genome sequencing (WGS) differ in the regions they examine and in the kinds of findings they may detect. There is no universal best first test. The choice depends on the child’s phenotype, the suspected mechanism, the test’s technical scope, and the laboratory’s interpretation and reporting policies.

Coverage and detection capabilities vary by laboratory. A panel may be updated over time; exome and genome tests differ in how well they detect copy-number changes, structural variants, and other variant classes. Before ordering, confirm what the laboratory’s specific assay can and cannot detect. The assay name alone does not settle that question.

A focused panel may be a sensible choice when clinical and immunological findings point toward a narrower group of genes. Broader sequencing may be considered when the phenotype is less specific, when a focused test has not resolved the case, or when the clinician is concerned about variant types outside the first assay’s scope. That is a clinical trade-off, not a general claim that one approach is more efficient or more cost-effective.

The diagnostic workup checklist for rare immune diseases should therefore include a question for the ordering clinician: what result would change the next clinical decision? The answer helps determine whether a narrow test is appropriate, whether broader analysis is warranted, or whether additional functional studies should come first.

Managing Pre-Test Counseling and Complex Genetic Findings

Informed consent for pediatric molecular diagnostics should be a conversation, not just a signature. Before testing, families need to understand the purpose of the assay, its limits, the categories of findings that may be reported, and how results could affect the child and relatives. The discussion should reflect the specific test and the laboratory’s policies.

Several possible outcomes deserve plain-language explanation:

• A pathogenic or likely pathogenic finding may support a suspected diagnosis, but its significance still needs to be considered alongside the child’s clinical and immunological findings.
• A variant of uncertain significance (VUS) is a genetic change for which the evidence is not sufficient to determine whether it causes disease. A VUS is not, by itself, a diagnosis and should not be treated as one.
• No explanatory finding does not rule out an immune disorder. The test may not cover the relevant region or variant type, the responsible gene may not yet be known, or the cause may not be detectable by the assay used.
• Unexpected findings may arise, depending on the test and reporting policy. Discuss in advance whether findings unrelated to the original question may be reported and what choices the family has.
• Family implications may follow from an inherited result. A finding in the child can raise questions about relatives, future pregnancies, or testing of parents and siblings.

The consent process should also cover sample and data handling in line with the laboratory and clinic’s policies. Families should know who will receive the result, how it will be discussed, and whom to contact with questions. If parental samples are requested, explain why they may help and what participation involves.

A negative result is not a clean bill of health, and a VUS is not a hidden confirmation. Both require the clinical team to return to the whole picture: symptoms, immune testing, family history, and the technical limits of the assay. Reanalysis may be worth discussing when the phenotype changes or when new evidence becomes available; whether and how it is offered depends on the laboratory and the clinical service.

The result is one part of the diagnosis. When sequencing is inconclusive, clinical assessment and functional immunology still matter.

Optimizing Sample Collection for Patients with Hematological Risks

Sample choice is usually straightforward for germline testing, but certain clinical histories change the calculation. Follow the receiving laboratory’s current instructions for sample type, container, minimum quantity, labeling, and transport; requirements differ between services and assays.

For many patients, a blood sample is used. Some laboratories accept saliva or a buccal swab for germline analysis. These alternatives are not interchangeable in every situation, and the laboratory should confirm whether they are suitable for the test being ordered.

Peripheral blood may not be an appropriate source of germline DNA after hematopoietic stem cell transplantation, in some hematological malignancies, or when somatic reversion or other blood-cell-specific changes are suspected. In these circumstances, discuss sample choice with the clinical genetics or laboratory team before collection. Cultured skin fibroblasts may be considered as a non-blood source, but they involve a different collection and processing pathway.

The requisition should state relevant treatment and transplant history. Immunoglobulin replacement, immunosuppression, prior transfusions, and cellular therapy may affect the wider clinical interpretation or the choice of sample, even when they do not alter the inherited sequence being tested. Do not assume the laboratory will infer these details from the medical record.

What the laboratory needs to see

A useful requisition connects the sample to the clinical question. Include, as applicable:

• A concise phenotype summary, including age at onset and the main infection or immune features.
• Relevant immune investigations, such as immunoglobulin levels and lymphocyte subsets; include newborn screening results if available.
• Family history, including affected relatives and consanguinity when relevant.
• Vaccination history, with live vaccines noted where known.
• Previous treatments, transfusions, and transplant history.
• The sample type and collection details requested by the laboratory.
• The ordering clinician’s contact information and the specific diagnostic question.

If records are incomplete, say so. A clear account of what is known—and what remains uncertain—gives the laboratory a better basis for interpretation than a confident but generic label. When the phenotype is complex, a brief discussion between the ordering team and the laboratory may clarify whether the requested assay and sample are appropriate.

The strongest preparation is not the longest requisition or the broadest sequencing test. It is a coherent account of why testing is being done, what the child’s immune findings show, and what the result might help the team decide. Molecular testing can sharpen that picture. It cannot replace the clinical work that makes the picture understandable.