A spirometry test measures lung function by assessing forced vital capacity (FVC), forced expiratory volume (FEV), and the FEV1/FVC ratio to diagnose respiratory diseases like asthma and COPD. Normal results generally indicate FVC and FEV1 values above 80% of predicted values, while a low FEV1/FVC ratio suggests an obstruction. Doctors interpret these results in relation to normal values based on individual factors, and further testing may be advised if results show abnormalities.

1. A Handy Guide To Help Interpret Spirometer
Readings
• A spirometry test is used to test how well your lungs are functioning. But the results can be a little
confusing. Read on to find out how to compare your readings with normal predicted values and
how to interpret FVC, FEV1 and FEV1/FVC Ratio results.
• If you have been diagnosed with a respiratory disease, like asthma or COPD – Chronic Obstructive
Pulmonary Disease, you may be aware of the spirometry test and its use in the diagnosis of such
conditions.
• But it can be difficult to understand the many different results provided, and how best to
interpret all these readings.
• Read this handy guide to find out just how you and your doctor can interpret spirometry readings
and what this may mean in the long term for your lung condition

2. What Is a Spirometry Test Used For?
• A spirometer is a test to see how well your lungs work. Usually, the
test itself will be conducted with your GP or a practice nurse at your
doctor’s surgery but it can be performed anywhere.
• The test is a helpful way for healthcare professionals to check your
lungs and airways to effectively diagnose a lung condition, such as
asthma, COPD, and restrictive lung disease (such as interstitial
pulmonary fibrosis).
• A spirometry test measures the volume of air you both inhale and
exhale, and how quickly you exhale.

4. There are crucial measurements derived from a
spirometry test and these include:
• ➞ Forced vital capacity (FVC)
• ➞ Forced expiratory volume (FEV)
• ➞ Forced expiratory volume in one second (FEV1)
• ➞ Total lung capacity (TLC)
• What Do Normal, Values in A Spirometry Test Mean?
• Results are given in litres per minute and percentages.

5. Normal readings for this test are different depending on the
person and they are based on the following factors:
• ➞ Age
• ➞ Height
• ➞ Race
• ➞ Gender

6. Your doctor will work out the predicted normal values for you
before you undertake the test.
Once the test is complete, they will then evaluate your test
score against the predicted value. To get a normal result? You
will need to obtain a score that is 80% or more of the
predicted value.
If you want to gain an idea of what your normal value looks
like, you can use a very clever device, called a spirometry
calculator.
Here, you can enter your own individual details – or if you
know your spirometry readings already – and the calculator
will work out what % of the normal, predicted values your
results are.

7. As the spirometry test measures two key
factors…
• ➞ Forced vital capacity (FVC)
• ➞ Forced expiratory volume in one second (FEV1)¬
• If your airways are obstructed, the amount of air you will be able to
quickly exhale from your lungs will be lower than normal.

8. The FEV1/FVC ratio will therefore be lower.
After you have your spirometry test, your doctor
compares your test results to the normal, predicted
values from people who are like you in age, height,
weight, gender, and ethnicity.
Normal results will have an FVC and a FEV1 above 80
percent predicted with a FEV1/FVC ratio that is greater
than 70 percent.
This can come across as a little confusing, so read on to
find out how best to interpret these results.

9. Interpreting Your Spirometry Results
After your spirometry test, your doctor will look at your
results and begin to interpret them. There are several
methods your doctor may choose to interpret your results.
To diagnose asthma, you will have a low FEV1 and low
FEV1/FVC reading. This is due it being more difficult for
the air to leave the lungs. This means that is an airway
obstruction.
Obstructive lung diseases include asthma and COPD
(chronic obstructive pulmonary disease).
When spirometry is used in conjunction with a
bronchodilator test, this usually means that patients will
take four puffs of an albuterol inhaler, wait for 15-20 mins
and then further readings will be taken.

10. The results of which help to separate asthma
from COPD.
• If the FEV1 reading increases by 12% albuterol, it means that the airway blockage is reversible. This reversibility is a sign of asthma.
• ➞ If the numbers for your FVC or FEV1 are decreased, your doctor will then need to look more closely into the results of your test.
• ➞ Your doctor will move on to look at the % (percent) predicted for both your FVC and FEV1.
• ➞ They will begin with looking at the % for your Forced vital capacity (FVC). This is to work out whether it’s in the normal range.
• ➞ If your FVC is lower than normal, something is obstructing your airways/breathing. This could be due to an obstructive lung
disease.
• ➞ The results will be different in both children and adults.
• ➔ Your doctor will likely then investigate the % for your Forced expiratory volume in one second (FEV1), again to see if this in the
normal range.
• ➔ This measurement will tell your doctor the severity of any breathing issues. If your FEV1 is lower than normal, this could mean
that you have a significant breathing obstruction.

11. ➔ As it can be measured quickly and easily at all stages of disease, FEV1 is strongly
recommended as the measurement of choice in COPD as:
➔ According to guidelines from the American Thoracic Society, the figures below show
what’s considered normal and abnormal when it comes to your FEV1 spirometry test
results:
➔ Doctors will then look at calculating your FEV1/FVC ratio.
➔ The higher the % worked out from your FEV1/FVC ratio, (minus a restrictive lung
disease causing an elevated FEV1/FVC ratio), the healthier your lungs are.
➔ A low ratio suggests that something is blocking your airways:
➔ An obstructive lung disease, like COPD, will have a % (percent) predicted of less than
70%.
➔ Your spirometry test results can help your doctor diagnose COPD and other chronic
lung diseases as well as informing your doctor just how much damage there is within
your lungs.
➔ At this point, if your spirometry test readings come back as abnormal, your doctor
may recommend further testing to find out is your breathing problems are caused by a
medical disorder
➔ This can include blood tests and sinus x-rays.
➔ However, your doctor may also be able to split your lung disease into further stages.
➔ Often, doctors will use two different types of staging system: the GOLD System and
the BODE Index.