5 Common mistakes when performing Spirometry

Spirometry is the most commonly performed test of pulmonary function and it plays a central role in the diagnosis and surveillance of respiratory disease.  Accurate spirometry testing, interpretation, and follow-up are vital to ensure patients are diagnosed correctly, placed on the correct treatment pathway and monitored effectively. 

Although the principles for achieving accurate and repeatable testing seem simple, performing accurate testing has many obstacles some of those most common are outlined below.


Patient demographics

It’s vitally important when performing spirometry that the correct demographics’ information is obtained prior to starting the test. This includes the patient’s date of birth, birth gender, height, weight and ethnicity. 

It is important that all this information is recorded correctly as it will have a significant impact on the interpretation of the test. In some centres with busy clinics, patients’ height may be measured with shoes on, or be estimated by the patient. This will give false predicted values and have an adverse effect on the interpretation, whereby you are most likely to see a false-positive result. Patients who are unable to stand should have their height estimated by the correct arm span equations.

The birth gender and date of birth are also crucially important, but common mistakes when performing Spirometry include the gender being input incorrectly. It’s extremely important this information is checked by the performing physiologist and/or health professional, prior to starting the test.

Confirming the patients’ ethnicity is also important, as the Global Lung Initiative have further developed correction values related to ethnicity, which should be available within your Spirometry software. 



Calibration is vitally important when performing measurements of flow and volume, regular and accurate calibration helps those performing spirometry trust the results generated.

Formally calibration is the process for establishing the relationship between sensor-determined values of flow or volume and the actual flow or volume. A 3-L calibration syringe is used to carry out calibration checks, this is the process used to validate that the device is within calibration limits, e.g. ±3% of true value. Calibration checks must be undertaken daily or more frequently if there are large temperature changes within the test area or if specified by the manufacturer.

To help reduce test errors, a calibration log should be recorded, and equipment which cannot successfully be calibrated should not be used. Biological controls, whereby a member of the laboratory staff regularly performs spirometry, helps further reduce the risk of equipment or calibration faults. There are also devices now available which are supplied with pre-calibrated flow sensors which saves valuable time within buy clinics, these can be verified by using the calibration syringe to maintain Quality Control.


Hesitation and or Slow start

Spirometry is a test of maximal effort, therefore, a slight hesitation or a delayed start can affect results, and so is one of the common mistakes when performing Spirometry. A hesitation in blowing out before the initial blast affects most spirometry test results early in the manoeuvre. Similarly, a test which is performed slowly or in a will have a delayed peak flow and in circumstances will falsely elevate the FEV1 – affecting test interpretation.

A manoeuvre showing these errors must not be used to measure  FEV1, but it may be used to validate the FVC  if it is consistent with other acceptable but less than perfect curves.

Since hesitation and or a slow start occurs early in the test, it is most easily seen in the flow-volume curve, which has its peak flow displaced to the right. 

Hesitation can falsely elevate the FEV1 and allow for misinterpretation of the flow-volume loop. 

In instances where this occurs, the subject/ patient should be asked to blow immediately or encouraged to blow with more force.

a.)   Flow volume loop

b.)flow volume loop

Figure 1. Demonstrates a clear hesitation before exhalation in picture a) due to the patient breath-holding before blasting out and in b) slow to reach peak flow. Both types of errors will affect FEV1 and these traces as such should be discarded  


Test selection

Common mistakes when performing Spirometry include incorrect test selection. This is made whereby non-acceptable or non-repeatable manoeuvres are selected, this error can often be made by novices or those who perform spirometry infrequently.

This can happen when those performing the test are more focused on the numerical data and not the flow-volume curve.

With changes in technology, the use of flow-volume curves is commonplace, but some centres may still use volume time curves (whereby cough can be less easily identified).

Poor test selection can quite often lead to false-negative or false-positive results. If you see the result below here, FEV1 is performed within ATS criteria for reproducibility, but we see an unacceptable manoeuvre with cough present, which has the highest FEV1. The selection of tests should not solely be focused on the highest attained numbers for FEV1 and FVC but should be performed with technically accepted manoeuvres free from significant artefact.   

flow volume loop

Figure 2. Demonstrates three manoeuvres with reproducible numbers for FEV1, however, the best-selected test had a cough – and it’s not a technically acceptable test the numbers for this although the best attained should not be used.


Glottis  Closure or  Breath Holding            

Commonly you can see airflow during exhalation suddenly cease before the lungs have been completely emptied.

Closing the vocal cords (glottis closure) and breath-holding both causes the volume-time curve to show an abrupt horizontal line. The flow-volume curve drops sharply to zero flow. This is another common mistakes when performing Spirometry.

The FVC is falsely reduced and may be misinterpreted as indicating a restrictive impairment. In addition, the FEV1/FVC ratio may be falsely elevated, resulting in a normal FEV1/FVC ratio even hiding a potentially obstructive impairment. Aside from this as the patient continues to blow there would be a distinct loud noise as the patient attempts to carry on blowing through a closed glottis. 

Glottis closure may be involuntary and should be documented when it cannot be corrected.  However, for breath-holding, it’s important to coach the subject/patient to blow ‘UNTIL TOLD TO STOP’, or encouraged to relax the throat and squeeze from the diaphragm until empty, glottis closure can be difficult to correct, a slow vital capacity may be beneficial and help validate vital capacity. 

flow volume loop

Figure 3. Demonstrates glottis closure, seen by a sudden drop in the flow volume loop to 0 flow and in the volume time graph by a distinct plateau. Here we can see the patient had attempted to carry on the blow this would most likely be a noisy part of the manoeuvre.


Want to Learn More?

If you are interested in finding out more about our range of Spirometry and PFT products, why not drop our sales team a message at sales@lovemedical.com or give us a call on 0161 976 2744 and one of our team will be happy to talk to you!



What is Spirometry?


Spirometry is considered a method of assessing Lung Function by measuring the “useful” volume of air in a patient, in simple terms, it is a dynamic breathing test to look at how much air an individual can inhale and exhale and how fast this can be done. Spirometry  is used to help monitor and diagnose asthma and chronic obstructive pulmonary disease (COPD) as well as several other conditions which affect breathing, and may also be used to monitor the effect of any treatments for chronic lung conditions. 

Spirometry systems are generally available as handheld devices and desktop-based devices which are generally more sophisticated and give more detailed results.


Indications for Spirometry

Some of the reasons why an individual may be referred for a spirometry test include: 

  • Persistent cough
  • Increased phlegm
  • Shortness of Breath
  • Dyspnoea
  • Wheeze 
  • Two or more chest infections over 12 months
  • Increase or change in respiratory symptoms
  • History of smoking + symptoms >35yrs of age
  • History of childhood asthma + symptoms
  • Significant occupational history + symptoms


Why is Spirometry used?

A Spirometry test may be performed to assess any signs or symptoms that may be caused by a chronic lung condition as it can help tell if narrowed or inflamed airways are obstructing your breathing. Conditions such as:

If a chronic lung condition has already been diagnosed, Spirometry may be used periodically to check the efficacy of medications and to monitor and control breathing problems. Spirometry may also be used before any planned surgery to check lung function is adequate for the rigours of an operation and is also being used within occupational health to screen for occupational-related lung conditions.


What does Spirometry involve?

Spirostik USBSpirometry manoeuvres should be performed with the subject in a sitting position, and the tests require the subject to breathe through a flow sensing device in several predetermined manoeuvres. The patient should use a nose clip to ensure air is blown through the mouthpiece.

The spirometry test involves 2 main parts, the first is a Relaxed or Slow Vital Capacity (SVC) test, which involves taking 3 tidal breaths followed by a big breathe in and then a long steady blow out until the subject’s lungs are empty. 

The second part is Forced Vital Capacity (FVC) test, which involves taking 3 tidal breaths followed by a big breath in and a hard and fast blow out until the lungs are completely empty. Each part should be repeated 3 times to ensure consistent results.

The patient may then be asked to perform a reversibility test to test an inhaler or another form of medication to see if this improves the patient’s breathing.



What does Spirometry measure?

Slow Vital Capacity (SVC) – This is the amount of air the patient can blow out during the relaxed manoeuvre.

Slow Vital Capacity (SVC)
Slow Vital Capacity (SVC)

Forced expiratory volume (FEV) – This is how much air the subject can force from the lungs it is usually expressed as FEV1 the amount of air that can be exhaled in one second. This measurement helps assess the severity of breathing problems. Lower FEV-1 readings may indicate a more significant obstruction.

Forced vital capacity (FVC) – This is the largest amount of air that can be forcefully exhaled after a single deep breath. A lower than normal FVC reading may indicate restricted breathing.

By looking at the curves created by the software, it is possible to understand the problems the patient may have. They usually follow one of 3 patterns, normal, obstructive and restrictive.

Normal – Results are within a normal range based on the reference values for someone with the patients demographic.

normal air flow
Normal flow loop

Obstructive – When air flows out of the patient’s lungs slower than it should (low FEV1) an obstructive pattern is seen, this is caused by conditions which narrow the lungs airways such as asthma and COPD. 

Obstructive Flow Loop
Obstructive Flow Loop

This can then be graded according to the severity with the help of a reversibility test.


FEV1 80%+ Predicted value


 FEV1 50-79% Predicted value


 FEV1 30-49% Predicted value

Very Severe

 FEV1 > 30% Predicted value


Restrictive – When there is a reduction in the amount of air you can breathe in, but the speed in which you breathe out is preserved, a restrictive pattern is seen. Conditions such as Pulmonary Fibrosis which affect the lungs ability to expand and hold a normal amount of air could be the cause, although this can also be seen in obese patients.

Restrictive Flow Loop
Restrictive Flow Loop

Occasionally both obstructive and Restrictive patterns can be seen in patients with severe emphysema or cystic fibrosis.

Depending on the spirometry results patients may be sent for further lung function testing, such as lung volumes which could be done via Body Plethysmography, Helium Dilution or Nitrogen Washout, or a Diffusion test.



Are there any risks to Spirometry tests?

Spirometry is generally a safe test. The subject should perform the test from a sitting position, in the event that the subject feels a shortness of breath the sitting position prevents falls.

As some of the tests requires some exertion, it isn’t generally performed in subjects who have had a recent heart attack or some other heart condition. Rarely, the test may trigger severe breathing problems.


Want to Learn More?

If you are interested in finding out more about our range of Spirometry and PFT products, why not drop our sales team a message at sales@lovemedical.com and one of our team will be happy to talk to you about how we can help!