What Is Spirometry, and Does My Child Need It?

What Is Spirometry, and Does My Child Need It?

If your child coughs at night, wheezes with colds, or runs out of breath before the other kids on the soccer field, someone has probably said the word asthma. Spirometry is one of the main tools doctors use to move from “probably asthma” to an actual diagnosis — and to check whether treatment is working once it starts.

What spirometry actually is

Spirometry is a breathing test. Your child breathes into a mouthpiece attached to a machine, and the machine records how much air they can move and how fast they can move it.

That’s it. No needles, no radiation, nothing swallowed. The hardest part is the effort it takes.

The reason it matters is that asthma is, at its core, a problem with air getting out of the lungs. Inflamed, narrowed airways don’t stop a child from breathing in very well. They slow down the breath out. Spirometry is designed to measure exactly that.

What your child has to do

A respiratory tech or nurse will have your child sit up straight, put a soft clip on their nose so no air escapes, and seal their lips around a mouthpiece.

Then they take the biggest breath they possibly can and blast it out as hard and as fast as they can — and keep blowing until they’re completely empty. For young children that means blowing for four to six seconds, which feels like a long time when your lungs are already empty.

They’ll repeat it several times. The test needs at least three good efforts that look similar to each other, so a session usually takes fifteen to thirty minutes including coaching and rest breaks.

Many places use animated software to make this easier — the child blows out birthday candles on a screen, or knocks over a row of blocks. Kids often need a lot of loud encouragement from the person running the test. That’s normal and it’s part of the job.

If the first round shows narrowed airways, your child may be given a dose of albuterol (a quick-relief inhaler medicine) and then repeat the test after about fifteen minutes. Comparing before and after is one of the most useful things spirometry can tell us.

The age question

Spirometry depends entirely on cooperation. A child has to understand the instructions, seal their lips, and give maximum effort several times in a row.

Most children can do a reliable test starting around age five or six. Some four-year-olds manage it beautifully with a patient, experienced coach. Some eight-year-olds have a rough first session and do much better on a second try a few months later.

Below that age, doctors generally diagnose asthma on the pattern of symptoms, the response to a trial of medication, family history, and physical exam findings. That’s a legitimate approach — it’s just less precise, which is why testing is added as soon as a child is developmentally ready.

If a session doesn’t produce usable results, it isn’t a failure. It usually just means trying again when your child is a bit older or feeling better.

What the numbers mean, in plain language

You’ll see a report with abbreviations. Here are the ones that matter most.

FVC (forced vital capacity) is the total amount of air your child blew out. Think of it as lung size on that day.

FEV1 (forced expiratory volume in one second) is how much air came out in the very first second. This is the headline number for asthma. Narrowed airways slow that first second down.

FEV1/FVC ratio compares those two. It tells us whether the problem is airways that are too narrow versus lungs that are simply small. In healthy children this ratio is high — typically above about 0.85 — and it tends to drop when airways are obstructed.

Percent predicted is how your child’s result compares to other children of the same age, height, sex and ethnicity. A number close to 100% means about average for their size.

Bronchodilator response is the change after albuterol. In children, an increase in FEV1 of roughly 12% or more is considered a meaningful improvement and points strongly toward asthma. Airways that open up in response to a rescue medication are, by definition, airways that were reversibly narrowed.

Your child’s doctor will interpret these together, not one at a time, and always alongside the story you tell about symptoms.

Why symptoms and history alone aren’t enough

Asthma gets both over-diagnosed and under-diagnosed, and testing helps with both problems.

Over-diagnosis happens because a lot of things cause coughing and wheezing in children. Recurrent viral infections, post-nasal drip from allergies, reflux, vocal cord dysfunction, and plain deconditioning can all look like asthma from the outside. Some children are put on daily inhalers for years without ever having had asthma.

Under-diagnosis happens because families adapt. Parents describe a child as “just not very athletic” or “always chesty with colds.” Children stop doing the things that make them cough, so the symptoms disappear along with the activity. On a questionnaire, everything looks fine.

Spirometry gives an objective measurement that doesn’t depend on how anyone remembers the last three months.

How results shape treatment

If testing supports asthma, the next question is whether your child needs a daily controller medication — usually a low-dose inhaled steroid — or whether a rescue inhaler used as needed is enough.

That decision rests on how often symptoms occur, how often they wake your child at night, how often the rescue inhaler gets used, whether activity is limited, and how many courses of oral steroids they’ve needed in the past year. Spirometry adds a hard number to that picture. Reduced lung function, even in a child who says they feel fine, generally pushes toward starting a controller.

Once treatment starts, spirometry is repeated to confirm it’s actually working. Guidelines generally suggest repeating it after treatment is established and stabilized, and then periodically — at least every one to two years for children with persistent asthma, and sooner if things change. You can talk with us about a testing schedule that fits your child’s pattern, and about how a written asthma action plan fits alongside it. Our page on asthma care covers what ongoing management involves, and if your child needs a rescue inhaler during the school day, this post walks through the paperwork side.

A normal test does not rule asthma out

This is the part families most often misunderstand.

Many children with asthma have completely normal spirometry when they’re well. Their airways are only narrowed during a flare — triggered by a virus, cold air, exercise, pollen, or smoke. Test them on a calm Tuesday in a quiet exam room and the numbers can look perfect.

So a normal result doesn’t close the case. If the story still strongly suggests asthma, the next steps might include an exercise challenge test, other specialized lung testing, or a monitored trial of controller medication to see whether symptoms improve. Sometimes a referral to a pediatric pulmonologist or allergist makes sense.

The reverse is also true: one abnormal test on a day your child had a cold doesn’t automatically mean lifelong asthma. Patterns over time matter more than any single result.

When to get checked sooner

Don’t wait for a scheduled test if your child is coughing most nights, needs a rescue inhaler more than twice a week, is limiting activity because of breathing, or has needed oral steroids more than once in a year. Those are signs current treatment isn’t holding, and a sick visit is the right move.

Call 911 for severe breathing trouble — struggling to speak in full sentences, skin pulling in around the ribs or at the base of the neck, blue lips, or a rescue inhaler that isn’t helping.

Talk with us

If you’re not sure whether your child’s cough is asthma, bring it up at their next visit or schedule an appointment. We can go through the history, examine your child, and discuss whether breathing testing is the right next step and where it fits. You can also reach out with questions before you come in.