Common Variable Immunodeficiency Test Panel: IgG, IgA, IgM, Vaccine Response, and Diagnosis

A common variable immunodeficiency test panel evaluates whether the body makes enough antibodies and whether those antibodies respond normally to vaccines. The core findings are persistently low IgG, usually low IgA and/or IgM, and impaired specific antibody production after other causes of hypogammaglobulinemia have been excluded. No single blood result confirms CVID.

Testing often begins after repeated sinus, ear, or lung infections, but CVID can also present with autoimmune blood-cell destruction, chronic diarrhea, enlarged lymph nodes, granulomatous disease, bronchiectasis, or unexplained inflammation. The evaluation must account for age, previous vaccinations, medicines, protein loss, cancer, infection, and any immunoglobulin replacement therapy. Vaccine titers are particularly time sensitive: they are usually measured before a diagnostic vaccine and again several weeks afterward. An immunologist combines this pattern with symptoms and additional immune studies to decide whether CVID, another antibody deficiency, or a secondary condition is more likely.

• CVID is not diagnosed by low IgG alone: IgG is usually reduced on repeat testing, with low IgA and/or IgM and impaired antibody function.
• Vaccine titers test antibody quality: Pneumococcal, tetanus, or diphtheria antibodies may be checked before and about 4–8 weeks after vaccination.
• Secondary causes must be excluded: Medicines, lymphoma, nephrotic syndrome, intestinal protein loss, and other disorders can mimic CVID.
• Immunoglobulin treatment changes the panel: Replacement IgG raises serum levels and contains donor vaccine antibodies, making some diagnostic tests unreliable.
• B-cell numbers may be normal: CVID often reflects poor B-cell maturation or antibody production rather than absence of all B cells.
• The panel also looks for complications: Blood counts, liver tests, lung assessment, lymphocyte subsets, and other studies are chosen from the clinical picture.

Table of Contents

• What a CVID Panel Is Designed to Show
• Symptoms and History That Prompt Testing
• Core Immunoglobulin Measurements
• How Vaccine Response Testing Works
• Additional Tests That Complete the Evaluation
• Excluding Secondary Hypogammaglobulinemia
• How Results Support or Argue Against CVID
• What Happens After Diagnosis

What a CVID Panel Is Designed to Show

Common variable immunodeficiency, or CVID, is a group of antibody-deficiency disorders rather than one uniform disease. The word “variable” reflects differences in age at onset, infection burden, immune complications, laboratory patterns, and genetic causes. Most patients have too little IgG and reduced ability to make effective antibodies against specific microbes.

A diagnostic panel addresses four separate questions:

1. Are total immunoglobulin concentrations low? IgG is central, with IgA and IgM providing classification and context.
2. Can the patient make antigen-specific antibodies? Vaccine-response testing evaluates function rather than total quantity alone.
3. Are B cells and other lymphocytes present? Flow cytometry can identify another combined or B-cell disorder.
4. Is there a secondary explanation? Protein loss, medication, malignancy, infection, or organ disease must be considered before CVID is assigned.

The panel is not standardized to one fixed list at every laboratory. A clinician may order quantitative immunoglobulins first and add vaccine titers, lymphocyte subsets, B-cell phenotyping, serum protein studies, and genetic testing in stages. This approach avoids drawing conclusions from a large panel without clinical context.

CVID is generally diagnosed after age four, because antibody levels and vaccine responses in younger children can still be maturing and transient hypogammaglobulinemia may resolve. Some patients are not recognized until adulthood even though earlier infections or immune symptoms were present.

A related immunoglobulin panel measures antibody classes, but a CVID evaluation goes further by testing function and excluding mimics. The diagnosis belongs to the whole pattern, not to the panel name printed on an order form.

Symptoms and History That Prompt Testing

Repeated bacterial respiratory infections are the classic reason to investigate CVID. Patients may have recurrent sinusitis, otitis media, bronchitis, or pneumonia, often with organisms such as Streptococcus pneumoniae or Haemophilus influenzae. Persistent infections can damage airways and lead to bronchiectasis.

Testing may also be appropriate when infections are unusually severe, require repeated antibiotics, recur soon after treatment, involve several anatomic sites, or occur with a family history of antibody deficiency. The number of common colds alone is less informative than culture results, imaging, treatment intensity, and complications.

CVID can present without a dramatic infection history. Other clues include:

• Autoimmune thrombocytopenia, autoimmune hemolytic anemia, or neutropenia
• Chronic diarrhea, weight loss, malabsorption, or inflammatory enteropathy
• Enlarged spleen, persistent lymph nodes, or unexplained liver abnormalities
• Granulomatous inflammation in the lungs, lymph nodes, liver, skin, or other organs
• Interstitial lung disease or declining lung function
• Recurrent Giardia or other gastrointestinal infection
• Poor growth in a child or adolescent
• Unexplained low globulin or total protein on routine chemistry testing
• A weak or absent response to vaccines despite documented vaccination

The history should include the age when problems began, infection sites, organisms, antibiotic courses, hospitalizations, chest imaging, autoimmune diagnoses, gastrointestinal symptoms, and cancers. Family history can reveal relatives with recurrent infections, low immunoglobulins, autoimmunity, early death, or lymphoma.

Medication history is equally important. B-cell-depleting agents such as rituximab, corticosteroids, some antiseizure drugs, immunosuppressants, and certain cancer therapies can lower immunoglobulins. The timing between treatment and the first low IgG result may identify a secondary cause.

A clinician also reviews previous immunoglobulin values. A new low IgG in an older adult with weight loss and enlarged nodes is approached differently from low levels documented since adolescence. Stable trends can help distinguish longstanding immune deficiency from an acquired change.

Core Immunoglobulin Measurements

The basic blood tests are IgG, IgA, and IgM. Results must be compared with age-adjusted laboratory ranges, especially in children. Adult reference intervals also vary among laboratories and assay platforms.

IgG

IgG is the main antibody class in blood and tissues. It supports opsonization, toxin neutralization, viral defense, and long-term responses to many vaccines. CVID requires a meaningful reduction in IgG, often defined relative to the laboratory mean or lower limit rather than one universal cutoff.

Low IgG should usually be confirmed on at least two measurements, separated in time, unless the deficiency is profound and treatment cannot safely wait. Temporary reductions can occur during acute illness, after certain medicines, or with protein loss.

The IgG blood test does not show whether the antibodies recognize the right targets. A patient can have moderately low IgG with adequate vaccine antibodies, or a near-borderline IgG with poor specific responses and significant clinical disease.

IgA

IgA protects mucosal surfaces in the respiratory and gastrointestinal tracts. Most diagnostic frameworks expect low IgA and/or low IgM in addition to low IgG. Markedly low IgA with normal IgG can indicate selective IgA deficiency rather than CVID, although some patients evolve over time.

The IgA level can help explain respiratory and gastrointestinal susceptibility, but the severity of symptoms does not track perfectly with the number.

IgM

IgM is important in the early antibody response and in defense against encapsulated bacteria. It may be low, normal, or occasionally elevated in patients being evaluated for CVID. Persistently high IgM with low IgG and IgA raises consideration of hyper-IgM syndromes or other immune dysregulation, particularly in younger patients.

IgG subclasses

IgG1, IgG2, IgG3, and IgG4 may be measured in selected cases, but subclass testing does not replace total IgG and vaccine responses. Low subclasses can occur in healthy people, and values vary with age and laboratory. A clinically meaningful subclass deficiency requires compatible infections and impaired antibody function.

How Vaccine Response Testing Works

Vaccine-response testing determines whether B cells can produce specific antibodies after a known antigen challenge. It is one of the most important functional parts of a CVID evaluation, but it requires careful timing and interpretation.

The clinician first measures baseline antibodies to selected vaccine antigens. A diagnostic vaccine may then be given, followed by repeat titers about four to eight weeks later. Common choices include pneumococcal polysaccharide antibodies and protein-antigen antibodies such as tetanus or diphtheria.

Pneumococcal antibody testing

A pneumococcal antibody titer test measures IgG against multiple pneumococcal serotypes. Interpretation considers how many serotypes reach a protective level, the fold increase from baseline, age, the vaccine used, prior conjugate vaccines, and the laboratory method.

There is no single percentage or concentration that applies to every patient. A high baseline titer may not rise fourfold even when protection is adequate, while a large fold rise from an extremely low baseline may still remain below a useful concentration. Modern vaccine history also matters because previous conjugate vaccines prime responses to overlapping serotypes.

Pure polysaccharide challenge has traditionally been useful for evaluating T-cell-independent antibody production, but vaccine recommendations and product availability change. The immunologist chooses an approach that is clinically and ethically appropriate for the patient’s age and current immunization status.

Protein-antigen titers

Tetanus and diphtheria antibodies assess response to protein antigens. A person may respond normally to protein vaccines but poorly to pneumococcal polysaccharides. This pattern can fit specific antibody deficiency or an IgG subclass problem rather than classic CVID, depending on total immunoglobulins and symptoms.

A diphtheria antibody test or tetanus titer should be interpreted using the laboratory’s protective threshold and the date of the last dose.

Effects of immunoglobulin replacement

Intravenous or subcutaneous immunoglobulin contains donor IgG, including antibodies to common vaccines. Once replacement therapy begins, serum IgG and vaccine titers no longer reflect only the patient’s own production. Diagnostic vaccine challenges are therefore best completed before treatment when clinically safe.

Stopping immunoglobulin solely to retest endogenous production can leave a patient unprotected and requires specialist supervision. The washout interval is long because infused IgG persists for weeks. In many established cases, clinicians rely on pretreatment records rather than interrupting effective therapy.

Preparing for vaccine-response testing is mostly about documentation. The patient should bring immunization records, dates of recent vaccines, prior titer reports, and any record of immunoglobulin infusions. The clinician should decide in advance which serotypes or protein antibodies will be measured and which laboratory will perform both the pre- and post-vaccine samples. Switching methods between the two draws can create apparent differences that reflect the assay rather than the immune response.

The post-vaccine sample should be collected within the requested window. Drawing too early may miss the full response, while drawing months later may confuse initial production with antibody persistence. If the patient becomes ill or receives immunoglobulin between samples, the specialist should decide whether the challenge remains interpretable. A missed time point is better acknowledged than forced into a misleading conclusion.

Protection and diagnostic response are related but not identical. A titer above a population-based protective threshold may reduce risk for one infection, yet CVID diagnosis depends on the breadth and quality of the response across antigens. Conversely, a low antibody concentration does not guarantee that a vaccinated person will become ill. Laboratory results support clinical judgment; they do not predict every future infection.

Additional Tests That Complete the Evaluation

The next tests are selected to distinguish CVID from other inborn errors of immunity and to identify complications.

A complete blood count with differential looks for lymphopenia, neutropenia, anemia, and thrombocytopenia. Cytopenias may reflect autoimmunity, infection, medication, hypersplenism, marrow disease, or another immune disorder. Reticulocyte count, bilirubin, haptoglobin, and direct antiglobulin testing may be added when hemolysis is suspected, although antibody-based tests can be less sensitive in an antibody-deficient patient.

Flow cytometry commonly measures:

• Total T cells (CD3)
• Helper T cells (CD4)
• Cytotoxic T cells (CD8)
• B cells (CD19 or CD20)
• Natural killer cells

Most people with CVID have circulating B cells, but some have reduced numbers. Very low or absent B cells may suggest X-linked agammaglobulinemia or another B-cell-development disorder. Significant T-cell deficiency may point away from uncomplicated CVID toward a combined immunodeficiency.

Specialized B-cell phenotyping can measure class-switched memory B cells, transitional B cells, plasmablasts, and CD21-low B cells. These patterns can support classification and may correlate with autoimmunity, lymphoid enlargement, or granulomatous complications. They do not replace the required clinical and immunoglobulin assessment.

Other studies may include:

• Serum protein electrophoresis and immunofixation
• Kidney and liver function tests
• Urinalysis and urine protein measurement
• Stool alpha-1 antitrypsin for intestinal protein loss
• HIV testing and other infection studies
• Chest CT and pulmonary function testing
• Tests for Giardia or chronic gastrointestinal infection
• Evaluation for celiac-like enteropathy, inflammatory bowel disease, or liver disease
• Bone marrow or lymph-node assessment when malignancy is suspected

Genetic testing is increasingly useful, especially with early onset, severe immune dysregulation, unusual infections, affected relatives, or features suggesting a defined monogenic disorder. Genes such as NFKB1, NFKB2, TNFRSF13B, CTLA4, LRBA, and others can produce CVID-like phenotypes. A variant does not always prove causation, and many patients have no identifiable single-gene explanation.

Excluding Secondary Hypogammaglobulinemia

CVID is a diagnosis of exclusion. The same low-IgG pattern can arise because antibodies are not produced, are being lost, are diluted, or are suppressed by treatment or disease.

Category	Examples	Helpful clues or tests
Medication	Rituximab and other B-cell therapies, corticosteroids, immunosuppressants, some antiseizure medicines	Drug timeline, B-cell counts, prior normal immunoglobulins
Protein loss	Nephrotic syndrome, protein-losing enteropathy, severe burns	Urine protein, serum albumin, stool alpha-1 antitrypsin
Blood or lymphoid disorder	Chronic lymphocytic leukemia, lymphoma, plasma-cell disease	Blood count, examination, electrophoresis, imaging, hematology evaluation
Infection	HIV and selected chronic infections	Targeted infectious testing
Other immune disorder	Combined immunodeficiency, agammaglobulinemia, thymoma-associated immunodeficiency	Lymphocyte subsets, age, imaging, genetics
Physiologic or transient	Infancy, temporary post-illness reduction	Age-adjusted ranges and repeat testing over time

The distinction matters because treatment and prognosis differ. Protein-loss disorders may improve when the underlying kidney or intestinal disease is controlled. Medication-induced deficiency may recover slowly after treatment ends, although some patients still need immunoglobulin replacement. Lymphoid malignancy requires its own evaluation and management.

Albumin and total protein can provide clues. Low IgG with low albumin suggests broad protein loss or reduced synthesis more than isolated antibody-production failure. Normal albumin does not exclude every secondary cause.

A careful pre-illness record is valuable. If immunoglobulins were normal before rituximab and fell afterward, secondary deficiency is more likely. If levels were already low and infections preceded treatment, an underlying primary disorder may have been unmasked.

How Results Support or Argue Against CVID

A typical supportive pattern includes recurrent or otherwise characteristic immune problems, repeatedly low IgG, low IgA and/or IgM, impaired response to vaccines, and no better secondary explanation. B cells are often present, although their mature subsets may be abnormal.

Findings that strengthen the case include:

• IgG clearly below the age-adjusted reference interval on more than one occasion
• Low IgA, with or without low IgM
• Poor response to both polysaccharide and protein antigens
• Reduced class-switched memory B cells
• Recurrent bacterial respiratory infection or bronchiectasis
• Autoimmune cytopenia, granulomatous disease, lymphoproliferation, or CVID-like enteropathy
• A pathogenic variant known to cause a compatible antibody-deficiency syndrome

Findings that argue for another diagnosis include absent B cells, profound T-cell lymphopenia, a clear medication cause, major protein loss, normal immunoglobulin concentrations with isolated poor pneumococcal response, or low IgA alone.

Specific antibody deficiency can produce recurrent respiratory infections and poor pneumococcal responses while total IgG, IgA, and IgM remain normal. Selective IgA deficiency involves very low IgA with generally preserved IgG and IgM. IgG subclass deficiency requires a reproducible subclass pattern plus clinically meaningful antibody dysfunction. These conditions can overlap or evolve, so follow-up matters.

A borderline IgG should not be dismissed or automatically called CVID. The immunologist considers the depth and persistence of the reduction, vaccine function, infection burden, complications, and whether treatment would change outcomes. Some patients are monitored as unspecified hypogammaglobulinemia until the pattern becomes clearer.

Autoantibody tests can be misleading in CVID because poor antibody production may produce false-negative ANA, tissue transglutaminase IgA, or other serology. Diagnosis of autoimmune or gastrointestinal complications may require imaging, biopsy, cell-based testing, or IgG-based alternatives rather than relying on absent antibodies.

What Happens After Diagnosis

Immunoglobulin replacement is the main treatment for clinically significant CVID. It can be given intravenously every few weeks or subcutaneously at shorter intervals. Dosing is individualized to reduce infections and protect organs, not simply to place the IgG number within a generic range.

Before treatment, clinicians often document baseline infection frequency, lung imaging, pulmonary function, blood counts, liver tests, kidney function, and vaccine responses. After treatment begins, follow-up tracks infections, antibiotic use, trough IgG when relevant, infusion reactions, lung health, gastrointestinal disease, autoimmunity, lymph-node or spleen changes, and cancer risk.

Replacement IgG helps prevent many bacterial infections but does not correct every immune abnormality. Patients can still develop viral infections, autoimmune disease, inflammatory lung disease, enteropathy, or lymphoma. New symptoms should not be attributed automatically to “low immunity.”

Vaccination plans are individualized. Inactivated vaccines are generally safe, but the antibody response may be weak and replacement products may affect measured titers. Live vaccines may be avoided in some patients depending on T-cell function and specialist guidance. Household vaccination and routine infection prevention can add protection.

Seek prompt medical care for high fever, breathing difficulty, chest pain, confusion, dehydration, persistent severe diarrhea, or signs of sepsis. Recurrent pneumonia, coughing blood, unexplained weight loss, enlarging lymph nodes, or falling blood counts also require timely assessment.

A well-designed CVID panel does more than produce a list of low values. It shows whether antibody quantity and quality are impaired, rules out treatable secondary causes, identifies a broader immune defect, and creates a baseline for protecting the lungs and other organs before irreversible damage develops.

Patients can make the evaluation more accurate by gathering pharmacy records, vaccine dates, old laboratory reports, imaging, culture results, and the number of antibiotic courses used in the previous year. Recording the organism and site of each infection is more useful than simply reporting that infections are “frequent.” A specialist can then compare objective disease burden with the immune findings and avoid both underdiagnosis and unnecessary lifelong treatment.

Normal results at one point do not always end follow-up. Immunoglobulin levels can decline over time in some patients with selective IgA deficiency, subclass deficiency, or an evolving CVID-like disorder. Repeat testing is guided by new infections, autoimmune features, falling globulin, or other clinical change rather than performed on a rigid schedule for everyone.

References

• Common Variable Immunodeficiency 2025 (Official Guidance)
• Common Variable Immunodeficiency 2025 (Review)
• Common Variable Immunodeficiency Disorders 2025 (Review)
• Current concepts: Common variable immunodeficiency 2025 (Review)
• Autoimmune Cytopenias in Common Variable Immunodeficiency Are a Diagnostic and Therapeutic Conundrum: An Update 2022 (Review)
• Diagnosis and Management of Antibody Immunodeficiencies 2021 (Guideline)

Disclaimer

CVID diagnosis requires specialist interpretation of repeated immunoglobulin levels, vaccine responses, age, symptoms, treatments, and alternative causes. This article is educational and cannot determine whether an individual needs immunoglobulin replacement or another therapy. Seek prompt care for severe infection, breathing difficulty, confusion, dehydration, or other rapidly worsening symptoms.