If you are coughing or having difficulty with your breathing, one of the first things to do is to consult with your healthcare provider. From there, you are likely to undergo a series of diagnostic tests for respiratory disorders to narrow down a possible cause.

Diagnostic tests assess various abilities of your lung function. Some check whether you can take in air properly, while others assess whether your lungs are utilizing the oxygen you breathe in. Further tests can screen for anything disrupting lung function. Finally, more invasive tests check internal structures and tissues within the respiratory tract.

This article will explore the different types of diagnostic tests and occasions during which they are generally recommended.

Non-Invasive Respiratory Tests

Standard Pulse Oximeter Testing

A pulse oximeter is one of the basic tests to assess oxygen capacity. It is often given a preliminary assessment for both underlying heart and lung conditions. The most frequently used pulse oximeters are attached to the tip of your fingers. However, others can be placed on the toes, nose, feet, ears, and forehead. Within a few seconds, it measures your pulse and oxygen saturation in percentage. Ideal oxygen saturation is above 95%¹.

Spirometry

This simple lung function test evaluates your ability to breathe. Before this test, you might need to stop taking certain medications and inhalers. Smokers should abstain for a minimum of six hours. During the test, you take a deep breath in and breathe out through a tube as quickly and completely as you can. Subsequently, you will get medication to open up the airways and assess whether your breathing is better.

This is often a simple preliminary test for underlying conditions which limit breathing capacity such as chronic obstructive pulmonary disease (COPD)².

Pulmonary Challenge Tests

Another name for these tests is provocation tests. The challenge or provocation can be a chemical or exercise.

The chemical challenge test is for those who might present to their doctor with signs of asthma³. Initially, the doctor conducts a spirometric evaluation (which we described above) to assess your baseline lung function. Following this, they will give a drug - methacholine. This narrows your airways, limiting your breathing. Spirometry is conducted every time the dose is increased. The doctor will stop the test when you experience wheezing and significant difficulty in breathing.

The exercise variant of this test is for those who notice asthma symptoms while exercising. With this test, your doctor will tell you to run on a treadmill (instead of giving you a chemical) and then will assess your pulmonary capacity through spirometry.
Peak Flow Capacity

Measuring your peak flow capacity is a relatively easy test. It measures the airflow out of your lungs. After taking a deep breath you will forcibly exhale through a plastic tube. You will repeat this at least three times for a more accurate assessment. A result of over 80% is good. However, consistently decreased values should point to further assessment for conditions such as asthma.⁴

Diffusion Capacity Test

During this lung function test, the doctor will give you a small dose of carbon monoxide along with tracer gas during inhalation. This will not be enough to cause harm. Tracers such as neon, helium, or methane are frequently used gases for this test. Once you breathe this mixture in, along with all the other natural gases, you will hold your breath for about ten seconds. Following this, you will blow out the air through a tube which will measure the amount of carbon monoxide absorbed.

This evaluates how well your lungs absorb oxygen. Conditions like COPD or occupational lung conditions⁵ can limit the amount of oxygen reaching the blood via the lungs.

Fractional Exhalation of Nitric Oxide (FeNO) Test

This test is specifically for those who have asthma. It helps to assess underlying inflammation. Similar to a few of the previous tests listed, in this test you will exhale through a tube until you feel your lungs are empty.

The results help to understand whether steroids will be useful in managing your asthma⁶. If steroids are already being used, their efficacy will be evaluated.

Plethysmography

For this pulmonary function test, you will sit in an enclosed space and breathe through a tube for 15 minutes. Plethysmography helps to assess the amount of air your lungs are capable of inhaling as well as the amount of air exhaled⁷: in short, your total lung volume. It helps to understand whether your surroundings or habits impact your lung capacity.

There are a few precautionary measures to make the results more accurate. These include no smoking for an hour before, along with no meals or alcohol for at least two hours prior. Patients who are on oxygen support will be taken off it for the duration of the procedure.

Non-Invasive Imaging Tests

Chest X-ray

You have likely had at least one chest X-ray in your lifetime. It is the most basic test done if there is a suspicion of possible underlying lung disease⁸. During a chest X-ray, you will sit or stand between a machine emitting the X-rays and a plate collecting the images.

Before the X-rays, you will be asked to take a deep breath. This is because lungs filled with air, along with the surrounding structures, are easier to visualize. In addition, you will, per instructions, move in different positions that assist with assessing different parts of the lungs.

Chest Computed Tomography

While the chest X-ray can visualize bigger opacities caused by infection such as pneumonia or larger lung tumors, small changes are often difficult to see. This is usually where a computed tomography, or CT, scan helps. With this scan, they create in-depth, two-dimensional images through cross sections at different levels of the chest.

During a CT scan, you will lie down on a table and the doctor will move you through the scanner. You might have to change into a gown depending on what area of your body they want to scan.

Due to the detailed images provided, a CT scan often helps to conclude diagnoses for conditions like pneumonia, tumors⁹, and conditions like pulmonary embolism¹⁰.

Chest Positron Emission Tomography

A positron emission tomography scan – a PET scan – follows similar principles to a CT scan; however, it helps to understand the innate metabolic functions of tissues and organs beyond simple images. A radioactive tracer dye is injected before scanning to help visualize both normal and abnormal metabolic functions.

PET scans often can detect abnormal metabolic activity from tissues before they show up as symptoms. A key use for PET scans is to detect lung cancers¹¹.

Chest Ultrasound

A chest ultrasound can help to assess the structures within the thorax such as the lungs, trachea, heart, aorta, and esophagus¹². Often an ultrasound is used to assess whether fluid is collected within the lungs or pleural cavity (surrounding the lungs). This fluid can be due to underlying inflammation, cancer, or infections.

Chest ultrasounds can help guide procedures such as thoracocentesis, which helps drain excess lung fluid, or assist with needle biopsies.

Angiogram of the Pulmonary Vessels

An angiogram generally helps to visualize blood vessels. A pulmonary angiogram assesses the function of the blood vessels coursing through the lungs. During angiography, a catheter is inserted either through your groin or arm and guided towards the heart and lungs. A contrast dye is injected through an IV line. The doctors take images while the dye moves through the blood vessels.

Angiograms help to note narrowing of blood vessels, widening of blood vessels (aneurysms), blockages such as noted with pulmonary embolism¹³ and if foreign bodies are trapped with blood vessels. This test can also help treat underlying clots if required during the procedure.

Invasive Respiratory Tests

Bronchoscopy

During this diagnostic test, a small, thin, flexible tube with a camera is slowly passed through your respiratory passages. The camera within the tube helps to highlight tumors, sources of bleeding, or obstruction with the respiratory passages. Bronchoscopy also allows physicians to collect biopsy samples for further testing.

Patients are under sedation for the duration of the procedure. To prevent complications, patients should stop eating or drinking a minimum of 12 hours before the procedure.

Today, technological advances have enabled robotic-assisted bronchoscopy¹⁴. These bronchoscopes are smaller and are operated by a robot that is controlled by the physician. The bronchoscope is guided through the lungs, creating 3-D maps of the internal structures.

Mediastinoscopy

Following a similar principle as that of a bronchoscope, a mediastinoscope investigates the area between the two lungs and the breast bone. The physician will make a small incision in your chest to allow for the scope to pass through.

This procedure is scarcely used. It is primarily considered to assess the extent of metastasis in cancers¹⁵, by taking lymph node samples. Additionally, it helps guide the course of treatment following the investigation.

Endobronchial Ultrasound

An endobronchial ultrasound (EBUS) uses a bronchoscope along with an ultrasound probe to assess parts of the respiratory pathway. It looks at the structures of the lung, surrounding organs, and lymph nodes. It can help define results observed during preliminary tests such as an X-ray.

Lung Biopsies

During preliminary diagnostic tests, such as chest X-rays or CT scans, nodules or abnormal masses can be noted¹⁶. To confirm a diagnosis in such cases, and to rule out cancer, a biopsy may be required.

Various ways to collect samples for biopsy include CT-guided biopsy or during a bronchoscopy. For pleural biopsies, a needle is passed between the ribs from the back into the pleura. Samples collected are sent to a pathology lab for a further conclusive diagnosis.

This is often a last resort diagnostic test when other tests are inconclusive or malignancy needs to be ruled out¹⁷.

Conclusion

Diagnostic tests for coughs are often recommended based on the severity and duration of the cough. In some instances, symptoms that are coupled with a cough such as fever, weight loss, or chest pain can indicate a possible underlying cause that can guide to the right types of diagnostic tests.

Additionally, along with routine tests for the lungs, other tests such as an EKG or echocardiogram might be suggested to rule out possible causes linked to the heart. Routinely, doctors also ask for blood work to have baseline indicators for any health conditions.

Finally, it is crucial to follow all the instructions given by your physician for any of the tests that are recommended. This will allow for a seamless experience during the diagnostic test.

1. Vold, M. L., Aasebø, U., Hjalmarsen, A., & Melbye, H. (2012). Predictors of oxygen saturation ≤95% in a cross-sectional population-based survey. Respiratory medicine, 106(11), 1551–1558. https://doi.org/10.1016/j.rmed.2012.06.016[↩]
2. Walker, P. P., Mitchell, P., Diamantea, F., Warburton, C. J., & Davies, L. (2006). Effect of primary-care spirometry on the diagnosis and management of COPD. The European respiratory journal, 28(5), 945–952. https://doi.org/10.1183/09031936.06.00019306[↩]
3. Seo, H. J., Lee, P. H., Kim, B. G., Lee, S. H., Park, J. S., Lee, J., Park, S. W., Kim, D. J., Park, C. S., & Jang, A. S. (2018). Methacholine bronchial provocation test in patients with asthma: serial measurements and clinical significance. The Korean journal of internal medicine, 33(4), 807–814. https://doi.org/10.3904/kjim.2017.043[↩]
4. Mehta, B., Garg, K., Ambwani, S., Bhandari, B., & Bhagat, O. L. (2016). Peak Expiratory Flow Rate: A Useful Tool for Early Detection of Airway Obstruction in School Children. In Open Medicine Journal (Vol. 3, Issue 1, pp. 159–165). Bentham Science Publishers Ltd. https://doi.org/10.2174/1874220301603010159[↩]
5. Hieba, E.G., Shaimaa, E.E., Dina, S.S. et al. (2020). Diffusion lung capacity for carbon monoxide correlates with HRCT findings in patients with diffuse parenchymal lung disease. Egypt J Bronchol 14, 39. https://doi.org/10.1186/s43168-020-00042-x[↩]
6. Heffler, E., Carpagnano, G. E., Favero, E., Guida, G., Maniscalco, M., Motta, A., Paoletti, G., Rolla, G., Baraldi, E., Pezzella, V., Piacentini, G., & Nardini, S. (2020). Fractional Exhaled Nitric Oxide (FENO) in the management of asthma: a position paper of the Italian Respiratory Society (SIP/IRS) and Italian Society of Allergy, Asthma and Clinical Immunology (SIAAIC). Multidisciplinary respiratory medicine, 15(1), 36. https://doi.org/10.4081/mrm.2020.36[↩]
7. Criée, C. P., Sorichter, S., Smith, H. J., Kardos, P., Merget, R., Heise, D., Berdel, D., Köhler, D., Magnussen, H., Marek, W., Mitfessel, H., Rasche, K., Rolke, M., Worth, H., Jörres, R. A., & Working Group for Body Plethysmography of the German Society for Pneumology and Respiratory Care (2011). Body plethysmography--its principles and clinical use. Respiratory medicine, 105(7), 959–971. https://doi.org/10.1016/j.rmed.2011.02.006 [↩]
8. Kelly B. (2012). The chest radiograph. The Ulster medical journal, 81(3), 143–148. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3632825/[↩]
9. Purandare, N. C., & Rangarajan, V. (2015). Imaging of lung cancer: Implications on staging and management. The Indian journal of radiology & imaging, 25(2), 109–120. https://doi.org/10.4103/0971-3026.155831[↩]
10. Moore, A., Wachsmann, J., Chamarthy, M. R., Panjikaran, L., Tanabe, Y., & Rajiah, P. (2018). Imaging of acute pulmonary embolism: an update. Cardiovascular diagnosis and therapy, 8(3), 225–243. https://doi.org/10.21037/cdt.2017.12.01[↩]
11. Greenspan B. S. (2017). Role of PET/CT for precision medicine in lung cancer: perspective of the Society of Nuclear Medicine and Molecular Imaging. Translational lung cancer research, 6(6), 617–620. https://doi.org/10.21037/tlcr.2017.09.01[↩]
12. Saraogi A. (2015). Lung ultrasound: Present and future. Lung India: official organ of Indian Chest Society, 32(3), 250–257. https://doi.org/10.4103/0970-2113.156245[↩]
13. Alshumrani, G., Al Bshabshe, A., & Mousa, W. F. (2021). Diagnostic yield of CT pulmonary angiography for pulmonary embolism in clinically suspected patients. Medicine, 100(22), e26213. https://doi.org/10.1097/MD.0000000000026213[↩]
14. Agrawal, A., Hogarth, D. K., & Murgu, S. (2020). Robotic bronchoscopy for pulmonary lesions: a review of existing technologies and clinical data. Journal of thoracic disease, 12(6), 3279–3286. https://doi.org/10.21037/jtd.2020.03.35[↩]
15. Zhao, H., Wang, J., Liu, J., Li, J., Jiang, G., Li, Y., Yang, F., Liu, Y., & Zhou, Z. (2008). Zhongguo Fei ai za Zhi = Chinese journal of lung cancer, 11(5), 672–674. https://doi.org/10.3779/j.issn.1009-3419.2008.05.029[↩]
16. Anzidei, M., Porfiri, A., Andrani, F., Di Martino, M., Saba, L., Catalano, C., & Bezzi, M. (2017). Imaging-guided chest biopsies: techniques and clinical results. Insights into imaging, 8(4), 419–428. https://doi.org/10.1007/s13244-017-0561-6[↩]
17. Borelli, C., Vergara, D., Simeone, A., Pazienza, L., Castorani, G., Graziano, P., Di Micco, C., Quarato, C., & Sperandeo, M. (2022). CT-Guided Transthoracic Biopsy of Pulmonary Lesions: Diagnostic versus Nondiagnostic Results. Diagnostics (Basel, Switzerland), 12(2), 359. https://doi.org/10.3390/diagnostics12020359[↩]

Dr. Michelle Frank

Michelle is a healthcare consultant and content creator with over six years of experience in the FemTech space. She contributes extensively to health forums, especially those centered on enabling wellness, advancing digital health, and FemTech solutions. She loves classic rock music, reading classic literature, and finding new spots in town for good food and some chai.