The goals of testing are to diagnose lung diseases, determine their causes where possible, and evaluate their severity. Many health practitioners will order blood gases to evaluate oxygen and carbon dioxide levels, lung or pulmonary function tests (PFTs) to help diagnose and monitor lung function, and chest x-rays and or CT (computed tomography) scans to look at lung structure. Other testing is performed to help diagnose specific conditions.
Some tests may be performed to help determine a person's health status and how well the lungs are working. Examples include:
- Blood gases – a blood sample collected from an artery is used to evaluate blood pH, oxygen and carbon dioxide
- Complete blood count (CBC) – to evaluate blood cells and check for anemia
- Comprehensive metabolic panel (CMP) – to evaluate organ function and chemical and electrolyte balances
Additional tests may be performed to help diagnose certain lung conditions:
- Cystic fibrosis tests
- Alpha-1 antitrypsin – to determine if a person has AAT deficiency
- Pleural fluid analysis – to investigate the cause of fluid accumulation between the chest wall and the outside of each lung; it may be due to, for example, cancer or infections.
- Allergy tests – may be ordered to determine asthma triggers
- Tests for pneumonia or other specific infections:
- Bacterial sputum culture and Gram stain – to diagnose lung infections caused by bacteria or fungi
- AFB testing – to diagnose tuberculosis or a nontuberculous mycobacteria (NTM) infection
- Blood cultures – to diagnose bacteria and sometimes yeast infections that have spread into the blood
- Influenza tests – to diagnose influenza (flu)
- Respiratory syncytial virus (RSV)
- Pertussis – to diagnose whooping cough
- Fungal tests
- Mycoplasma tests
- Legionella tests
- Tests for autoantibodies may help determine if an autoimmune disorder is affecting the lungs:
- Lung biopsy – to evaluate lung tissue for damage or for cancer (see the article on Anatomic Pathology for more on this)
- Lung cancer tests for targeted therapy – the following tests may be performed on biopsy samples to help determine whether treatments that target certain types of lung cancer will be effective:
- EGFR gene mutation – if present, a person is more likely to respond to tyrosine kinase inhibitor drug therapies such as gefitinib and erlotinib.
- KRAS gene mutation – if present, a person is less likely to respond to tyrosine kinase inhibitors.
- ALK gene mutation / gene rearrangement (EML4-ALK) – if a mutation is present, the cancer is more likely to respond to ALK kinase inhibitors such as crizotinib and less likely to respond to tyrosine kinase inhibitors.
- ROS1 gene mutation – those with gene rearrangement are more likely to respond to crizotinib and less likely to respond to tyrosine kinase inhibitors.
- Sputum cytology – to evaluate lung cells for abnormal changes or for cancer
- Soluble mesothelin-related peptides (SMRP) – to monitor mesothelioma, a specific type of lung cancer
- Drug screen – to detect drugs in overdoses that can lead to decreased respiration or acute respiratory distress
- Fetal lung maturity (FLM) tests – used to evaluate the lung maturity of a fetus and may include tests for lecithin/sphingomyelin (L/S) ratio, phosphatidylglycerol (PG), foam stability index (FSI), or lamellar body counts (LBC); may be used to determine age of gestation before cesarean delivery or when a preganant woman is having symptoms of premature labor.
Lung function tests (pulmonary function tests, PFT)
A few of the more common tests are listed below. For more complete information, visit the web site for Johns Hopkins Medicine: Pulmonary Function Laboratory.
- Spirometry – measures the amount and rate of air exhalation as a person blows out through a tube; it is performed to evaluate narrowed or obstructed airways.
- Oximetry – measures the oxygen saturation of the blood using a small device placed on a person's finger
- Exercise stress test – monitors lung function on a person while they are on a stationary bike or treadmill
- Air flow with a peak flow meter – measures the rate of exhalation; it can be used at home by people with asthma to help monitor their condition.
- Lung volume – the quantity of air a person takes into their lungs and how much is left in the lungs after exhalation; it helps evaluate the elasticity of the lungs, the movement of the rib cage, and the strength of the muscles associated with respiration.
- Diffusing capacity measurement – assesses the transfer of oxygen from the lung air sacs to the bloodstream by evaluating how much carbon monoxide is absorbed when a small quantity is inhaled (not enough to harm)
- Chest x-ray – to look at lung structure and chest cavity
- CT (computed tomography) scan – a more detailed evaluation of lung structure
- MRI (Magnetic resonance imaging) – detailed pictures of organs and vessels in the chest
- Ultrasound – used to detect fluid between the pleural membranes
- Nuclear lung scanning – used to help detect pulmonary embolism and, rarely, to evaluate the effectiveness of lung cancer treatment
- Positron emission tomography (PET) scans – used to help diagnose lung cancer
For more on these, see the RadiologyInfo.org website.