Frequent Colds in Adults: Which Lab Tests Actually Help

“I’m sick every month, my immune system must be weak” — that is how the conversation starts in a primary care office in autumn and winter. The request usually follows: order me an immunity test, something that will show why my body can’t cope.

The conversation is worth starting with two inconvenient facts. First: frequent colds in an adult are rarely a problem with the immune system — far more often the explanation lies in the nose, in habits, and in the surroundings. Second: the “immunity test” people picture does not exist, but a short set of tests does, and it answers specific questions — is there hidden inflammation, undiagnosed diabetes, an antibody deficiency, or protein loss.

Below: how many respiratory infections a year count as normal, what most often masquerades as colds, which tests are worth running, and which signs call for an appointment rather than a lab slip. Every marker mentioned here has its own page in our lab test reference, so we won’t repeat them twice.

How many colds a year is normal

Let’s start with the number that removes half the worry. According to the US Centers for Disease Control and Prevention, adults average two to three colds a year, and children noticeably more. Other major sources give a slightly wider range: two to four episodes for an adult and six to ten for a child, and among children in daycare or school the count reaches twelve a year.

There are predictable differences between people, too. Women aged 20–40 get sick more often than men — largely because they have more contact with children. After 60 the average frequency drops below one episode a year: a lifetime accumulates immunological memory against hundreds of respiratory virus variants. That is exactly why “I never used to get sick and now it’s every month” in a young parent is almost always a story about daycare rather than about a broken immune system.

Children follow their own logic: through the first two or three years of daycare a child works through dozens of new viruses, and a dense run of episodes from autumn to spring is the expected picture, not a sign of malfunction.

The practical conclusion: the number of episodes on its own is a poor criterion. What matters far more is how each cold behaves. An ordinary respiratory infection lasts about a week, resolves without antibiotics or complications, and does not keep you from getting back to your life. A different picture is the one that warrants attention: a drawn-out course lasting more than ten days without improvement, recurrent purulent ear and sinus infections, pneumonias, the need for antibiotics several times a year.

What often masquerades as frequent colds

Before hunting for a fault in the immune system, it is worth testing a simpler hypothesis: are these colds at all? Adults often call any blocked nose with a runny discharge a “cold,” and that has plenty of causes.

• Allergic rhinitis. Year-round allergy (dust mites, pets, mold) produces congestion, sneezing and clear discharge that are easy to mistake for an endless run of infections. The distinguishing features are itching in the nose and eyes, the absence of fever, and a link to a place and a season. When IgE and skin tests are needed and when a trigger diary is enough is covered in our guide to allergies and atopy.
• Chronic rhinosinusitis. This is no longer a series of episodes but continuous inflammation of the nasal and sinus lining lasting 12 weeks or more. According to the StatPearls review, it is marked by congestion, thick discharge, a sense of facial pressure, and reduced sense of smell, and confirming it requires endoscopy or a CT scan rather than a blood test. In US statistics about 12% of adults reported it in the past year — and some of them spend years being treated for “allergies.”
• Vasomotor and rebound rhinitis. Persistent congestion without allergy or infection, including after months of using decongestant nasal sprays.
• Cough-variant asthma and postnasal drip. If every “cold” ends in a cough that lasts three or four weeks, the question belongs to a pulmonologist.
• Reflux. Acid reaching the throat causes a morning cough, throat clearing and hoarseness, which also read as an “eternal cold.”

Then there is contact frequency. An open-plan office, rush-hour public transport, a preschooler at home and monthly flights genuinely increase the number of encounters with viruses. That is not about immunity but about exposure, and no lab marker will show it.

Sleep, smoking and daycare: what actually raises the risk

Some factors have direct evidence behind them, and the first of these is sleep. In an experiment using rhinovirus challenge, where the sleep of 164 healthy volunteers was recorded for a week with a wrist actigraph before the virus was dropped into everyone’s nose, the risk of falling ill in those who slept less than 6 hours was roughly four times higher than in those who slept more than 7 hours (odds ratio 4.24 for 5–6 hours and 4.50 for under 5 hours). In people sleeping 6–7 hours there was no significant rise — meaning the threshold sits at around six hours.

What else shifts the probability of getting sick:

• Smoking and vaping — damage to the ciliated epithelium that normally clears mucus and viral particles out of the airways.
• Sleep apnea. Snoring, breathing pauses and daytime sleepiness mean broken, low-quality sleep every night. How to suspect apnea at home and when a sleep study is needed we covered separately in the piece on sleep apnea and snoring.
• Chronic stress — sustained strain changes how immune cells work; this is not a reason to “get cortisol tested,” but it is a reason to take your routine seriously.
• Inactivity, excess weight, low dietary protein — a more modest contribution, but a real one.
• Missed vaccinations. Flu and pneumococcal vaccines do nothing against rhinoviruses, but they remove from the year precisely the episodes most likely to end in complications.

If the feeling of “being sick all the time” comes bundled with fatigue that does not lift after a holiday, it helps to look at the situation more broadly — which markers sit behind that is covered in the piece on why you always feel tired.

The baseline set of tests for frequent colds

International guidance builds the workup in two stages, and the first is entirely doable at the primary care level. According to a 2025 review of immunodeficiencies in adults, the starting set looks like this:

Two important caveats. First: these tests are worth running not at the height of a cold but 4–6 weeks after an acute infection — otherwise both the differential and the immunoglobulins will show the response to current inflammation rather than your baseline. Second: where tuberculosis is common, chest imaging and TB testing belong in the basic workup, especially if the colds come with a lingering cough; whether that is routine depends on where you live.

What to do with the results if the form comes back with abnormal inflammatory markers is covered in detail in the piece on CRP, ESR and the complete blood count.

Red flags: when you need a doctor rather than a test

The European Society for Immunodeficiencies (ESID) lists the signs that mean the workup should go deeper — one from the list is enough:

• Four or more infections a year requiring antibiotics — ear infections, bronchitis, sinusitis, pneumonia.
• Two or more severe bacterial infections — osteomyelitis, meningitis, sepsis, cellulitis.
• Two radiographically confirmed pneumonias within three years.
• An infection in an unusual site or caused by a rare organism.
• A family history of primary immunodeficiency.

In adults, that list is extended with bronchiectasis of unclear origin, chronic diarrhea with weight loss, persistently enlarged lymph nodes and spleen, poor response to vaccination, and the appearance of autoimmune disease. It is worth understanding the limits of such lists: for a similar set of criteria from the Jeffrey Modell Foundation, sensitivity is around 56% at a specificity of 16% — in other words, this is a filter for referring someone to a specialist, not a test that confirms or excludes anything.

Immunoglobulins IgG, IgA and IgM: what the “immunity test” shows

If any test deserves the name “immunity check” in the first line, it is immunoglobulin levels — the antibody proteins produced by B lymphocytes. There are three main classes: IgG (the main defense, long-term memory), IgA (protection of mucosal surfaces — nose, bronchi, gut) and IgM (the first response to a new infection).

Selective IgA deficiency is the most common inborn immune defect: according to StatPearls, prevalence in European populations is estimated at between 1 in 150 and 1 in 3,000. The diagnosis is made after age four when IgA is below 7 mg/dL with normal IgG and IgM. An honest detail matters here: most people with this deficiency do not get sick more often than anyone else and learn about it by chance. Some do have recurrent respiratory and gut infections, allergies and autoimmune disease.

Common variable immunodeficiency (CVID) is rarer, but it is the most common symptomatic immunodeficiency in adults, and it can declare itself at 20, at 30 and at 40. The picture is not made up of recurrent bronchitis and pneumonia alone: a third of patients have autoimmune features, and chronic diarrhea, enlarged lymph nodes and bronchiectasis occur. The 2025 review names IgG below 4 g/L as the threshold for a deeper workup, with pneumonia risk rising markedly below 3 g/L.

Wizey’s chief medical officer, Dr. Aigerim Bissenova, notes that a low IgG or IgA on a single form is not yet a diagnosis: the values need rechecking outside an acute infection and must be read against the medications the person is taking. The next steps — lymphocyte subsets, assessment of the antibody response to tetanus and pneumococcal vaccines, and genetic testing where needed — are the immunologist’s territory.

Vitamin D, iron and zinc: what to expect from them

This is the most popular trio of requests when colds are frequent, and two things need separating here: finding a deficiency is useful, but expecting that correcting it will remove respiratory infections from your life is not.

Vitamin D. Back in 2021 a pooled analysis of 37 trials showed a small protective effect. The updated 2025 meta-analysis, covering more than 61,000 people across 40 trials, did not confirm that conclusion: the odds ratio for acute respiratory infection was 0.94 (95% CI 0.88–1.00) at p=0.057, with no differences by age, dose or baseline vitamin D level. Checking vitamin D still makes sense — deficiency is common at higher latitudes from late autumn through early spring, and the vitamin matters for bone and muscle. How to read the result by season and how not to overdo the dose we covered in the pieces on vitamin D norms and correction and on vitamin D overdose.

Iron and ferritin. “Low iron means more colds” sounds logical, but the data in adults do not support it. In three years of follow-up in the DO-HEALTH trial among people over 70, iron deficiency did not increase the frequency of upper respiratory infections (rate ratio 0.97). It was, however, associated with more severe infections requiring hospitalization. Checking ferritin is worth doing — but for fatigue, hair shedding, breathlessness and anemia, not for the cold counter.

Zinc. According to the 2024 Cochrane review, zinc probably does not prevent colds; it may shorten one already under way by about two days, but the certainty of that evidence is low and adverse effects (taste disturbance, nausea) are more common. Routinely measuring zinc in blood for frequent respiratory infections adds little: the test poorly reflects tissue stores.

Secondary causes: diabetes, medications, HIV and protein loss

In adults, acquired (secondary) causes of a weakened immune response are far more common than inborn ones — and a large part of the baseline test set is aimed precisely at them. According to the same 2025 review, the main groups are:

• Medications — the most common cause. Glucocorticoids, methotrexate, mycophenolate, TNF-α inhibitors (infliximab, etanercept), rituximab, JAK inhibitors, some anticonvulsants.
• Metabolic and endocrine conditions — diabetes, obesity, cortisol excess, thyroid dysfunction.
• Chronic infections — HIV above all; infection risk tracks directly with the CD4 lymphocyte count.
• Protein loss — nephrotic syndrome, inflammatory bowel disease, celiac disease: along with protein, the body loses antibodies.
• Chronic organ disease — kidney failure, liver cirrhosis, and the state after removal of the spleen.
• Undernutrition — a shortfall of protein and calories, and with them zinc, iron, and vitamins A and D.
• Blood cancers — leukemias, lymphomas, myeloma and their treatment.

Hence the logic of the set: HbA1c looks for diabetes, albumin for protein loss, the HIV test closes off the infectious cause — and the question “which medicines do you take regularly?” solves the problem more often than an extended immunology panel does.

Why an extended immune panel is not the first step

Panels marketed as an “immune status check” — dozens of parameters at once, sometimes with a promise to select an immunomodulator by the result — are easy to order in many places, including direct-to-consumer. Frequent colds are usually named right there in the indications. Here is why that is a poor starting point.

First, the order of the workup is reversed. Simple tests come first, looking for common and treatable causes; only then come lymphocyte subsets, vaccine response testing and complement activity. An extended panel without clinical context produces a set of numbers that is almost impossible to interpret: abnormal values turn up in healthy people, and a normal result does not exclude immunodeficiency.

Second, some of what these panels sell has no place in international guidance at all. “Interferon status with selection of immunomodulators” is a practice that exists mainly in certain national traditions of medicine; the diagnostic guidelines for immunodeficiency do not include it. The main risk here is not the price of the test but that its result becomes the justification for courses of immune-boosting drugs with unconvincing evidence behind them.

Third, most people who complain of frequent colds do not have a primary immunodeficiency — and the money spent on a thirty-parameter panel would do more good at an ENT appointment with nasal endoscopy. This does not mean an in-depth immunological workup is never needed: with the red flags listed above it is essential — but it is ordered by an immunologist and follows the results of the first stage.

Frequently asked questions

How many colds a year is normal? For an adult the benchmark is two to three colds a year; for a child in daycare or school, six to ten episodes — sometimes up to twelve — is considered normal. People over 60 get sick less often. What matters is not the count so much as the course: an ordinary cold clears within a week without antibiotics and without complications.

Which lab tests should I run for frequent colds? The first line is a complete blood count with differential, C-reactive protein and ESR, glucose or HbA1c, an HIV test, total protein and albumin, TSH, and immunoglobulins IgG, IgA and IgM. Vitamin D and ferritin are not tested “for immunity” but to find common deficiencies. Test 4–6 weeks after an acute infection rather than in the middle of one.

Do I need an immune panel if I get sick every month? Not as a first step. The workup for immunity runs in two stages: simple tests first (complete blood count, immunoglobulins, ruling out HIV, diabetes and protein loss), and only if something is off — or a warning sign is present — lymphocyte subsets and vaccine response testing. An extended panel is ordered and interpreted by an immunologist.

Does vitamin D help you get fewer colds? In pooled data from 40 randomized trials and more than 61,000 participants (2025), vitamin D supplementation did not significantly reduce the risk of respiratory infections: odds ratio 0.94 with p=0.057. The effect did not depend on baseline vitamin D level or dose. Checking 25(OH)D and correcting a deficiency is worth doing for other reasons, not as cold prevention.

When are frequent colds a reason to see an immunologist? If the past year brought four or more infections needing antibiotics, two or more severe bacterial infections, two radiographically confirmed pneumonias within three years, an infection in an unusual site or caused by a rare organism — and also with bronchiectasis, chronic diarrhea with weight loss, or a family history of immunodeficiency.

My child is sick every month — is that an immunodeficiency? Usually not. In the first two or three years of daycare a child meets dozens of new viruses, and six to ten episodes a year is the expected picture, particularly between autumn and spring. What is concerning is not the colds themselves but recurrent ear infections and pneumonias, severe bacterial infections, and faltering growth and weight.

Conclusion

Frequent colds in an adult are more often a story about the nose, sleep and surroundings than about the immune system. The sensible route looks like this: count the episodes and their severity honestly, rule out allergic rhinitis and chronic rhinosinusitis, look at sleep, smoking and medications, run the short baseline set of tests outside a flare — and only with red flags go to an immunologist for a deeper workup.

If the forms have already piled up and you would rather see them together than one at a time, that is what we build Wizey for: it helps connect markers to one another and put together questions for your doctor. It is not a substitute for an appointment, but a way to arrive at one prepared.