Most people who end up getting evaluated for a primary immunodeficiency did not start out thinking that was the problem. They started out noticing they were sick again. Another sinus infection. Another round of antibiotics. Another month where they never quite felt well before the next thing arrived. At some point a doctor, or the patient themselves, started asking why.
That question is where the workup begins.
Primary immunodeficiency disorders, of which there are now well over 400 recognized types, are conditions where some part of the immune system is either missing, too low, or not working the way it should. They are not rare in the way people assume. Mild to moderate forms are frequently underdiagnosed, partly because the symptoms look exactly like ordinary bad luck with infections for years before anyone thinks to look deeper.
If you or someone in your family has been referred for an immunodeficiency evaluation, here is what to actually expect.
It Starts With the History, and That Part Matters More Than You Think
Before a single blood test gets ordered, a good immunologist spends a significant amount of time in conversation. Not as a formality but because the pattern of illness in someone’s life is often more informative than any one lab result.
The questions tend to cover a lot of ground. How many infections per year, and what kind. Whether infections tend to require antibiotics to clear or resolve on their own.
Whether standard vaccines produced normal responses or seemed not to take. Whether certain types of infections, bacterial, viral, fungal, parasitic, tend to recur more than others.
Family history, because many primary immunodeficiencies follow inheritance patterns. Whether the person had any unusual infections, the kind that tend not to bother healthy immune systems at all.
That last category is particularly telling. Certain organisms that the immune system of a healthy person handles without incident become recurrent problems when specific immune pathways are not functioning.
Knowing which organisms keep showing up helps point toward which part of the immune system to examine first.
The Initial Blood Work and What It Is Actually Measuring
The first round of laboratory testing in a primary immunodeficiency workup is usually a broad survey. The goal at this stage is not to identify a specific disorder but to understand which areas of the immune system warrant closer attention.
A complete blood count with differential tells the physician how many of each immune cell type are circulating. Low lymphocyte counts, low neutrophil counts, or abnormalities in the ratios between cell types can each suggest different categories of immune dysfunction.
Immunoglobulin levels, specifically IgG, IgA, and IgM, measure the major antibody classes the body produces to fight infection. Low levels across the board suggest one category of problem. Low levels in a single class with normal levels in others point somewhere different. The pattern matters.
Beyond the totals, the workup often includes vaccine antibody titers. The question being asked is not just whether immunoglobulin levels look adequate on paper but whether the immune system actually produced a useful response to specific challenges it was supposed to have mounted a response to. A patient can have borderline immunoglobulin levels and make robust responses to vaccines, or they can have normal levels on paper and demonstrate very poor functional antibody production. Functional testing changes the picture considerably.
Looking More Closely at T Cells, B Cells, and Beyond
If initial testing suggests something is off, the next layer of evaluation goes into specific lymphocyte populations. Lymphocyte subset panels identify the numbers and percentages of T cells, B cells, and natural killer cells. From there, further analysis can break those populations down into subsets, naive versus memory B cells, helper versus cytotoxic T cells, and so on.
This matters because different conditions affect different populations. A person who looks relatively normal on a basic blood count might have a severe reduction in a specific T cell subset that only becomes visible when someone goes looking for it.
Complement testing is another component that gets added depending on the clinical picture. The complement system is a set of proteins that works alongside antibodies to clear infections and damaged cells. Deficiencies in complement, particularly in the later components, are associated with very specific vulnerability to certain bacterial infections. If that pattern shows up in the history, complement levels get checked directly.
Neutrophil function testing comes into play when there is a history suggesting problems with how the body handles bacterial and fungal infections despite what looks like normal cell counts. Having the right number of neutrophils matters less than whether they are actually capable of killing what they engulf.
Genetic Testing and When It Enters the Picture
While certain immunodeficiencies have an identified genetic basis. In select circumstances, most notably when a particular disorder is highly clinically and laboratory suspected, genetic testing can establish or confirm the diagnosis as well as the precise mode of inheritance and guide medical management and family counseling considerations.
For most workups, genetic testing is not the first approach. Usually, it comes later, once the clinical and laboratory picture has already pointed somewhere quite clearly. Pinpointing the exact genetic etiology, particularly in children, can lead to alterations in management.
Diagnosis Is Not Always a Clean Line
One thing worth saying plainly is that immunodeficiency workups do not always end with a clear answer immediately. Some patients have lab findings that fall in ranges where clinical judgment, longitudinal follow-up, and repeat testing over time are part of how the picture eventually becomes clear. Others get a straightforward answer in the first round.
The workup is not a one-time event in every case. Some conditions require monitoring of immunoglobulin levels over time, or repeat functional testing after deliberate vaccine challenges, before a diagnosis can be made confidently.
Sitting with an incomplete answer for a period of time is uncomfortable, especially when the question behind it is why you keep getting sick. The point of working with an immunologist who has done this for a long time is that they can tell the difference between a pattern that needs to be watched and one that needs to be acted on now.
Why Seeing an Immunologist Specifically Makes a Difference
Primary care physicians can order initial labs and notice patterns that raise concern. Moving beyond that point requires training and clinical experience that is specific to immunology. The interpretation of a complex lymphocyte subset panel, the decision about when a functional vaccine challenge is warranted, the ability to recognize a presentation that fits a less common primary immunodeficiency, these are not standard primary care territory.
Dr. Laura Ispas at Allergy Asthma Immunology has spent over 25 years evaluating and managing immune-related conditions in both children and adults in the Leesburg, Virginia area. The practice sees patients for primary and secondary immunodeficiency alongside the full spectrum of allergy and asthma care.
If you or your child has a history of frequent, severe, or unusual infections and have not been evaluated by a specialist, the workup is far less intimidating than most people expect. Same-week appointments are available when the schedule allows.
Call or text (571) 399-5132 or book directly at allergy-asthma-immunology.com
