Acute Respiratory Distress Syndrome (ARDS): Diagnosis Make an Appointment Refer a Patient Ask a Question Reviewed by James K. O'Brien, MD, FACP, FCCP (April 16, 2020) How is acute respiratory distress syndrome (ARDS) diagnosed? A variety of diagnostic tests are used to help diagnose ARDS. These tests determine how well the lungs are functioning, rule out other conditions with similar signs and symptoms, and identify the source of the infection. Tests for acute respiratory distress syndrome can include imaging, blood tests, analyzing sputum (the mixture of saliva and mucous that is coughed up) identify possible sources of acute respiratory distress syndrome. Chest X-rays show images of organs, tissues and bones in the chest area. It can show abnormalities including fluid or pneumonia in both lungs. Sometimes a patient with ARDS will be mistaken for having heart failure. Blood cultures examine blood samples for infection caused by bacteria, yeasts, fungi and viruses. These tests identify the infection in the blood and help the doctor determine what is causing ARDS. Blood gas tests show low oxygen levels in the blood. Sometimes the CO2 level will be low because the patient is hyperventilating to maintain their oxygen level. This test indicates how well the lungs are working. Sputum samples look at the substance that is coughed up to help identify the infection. Sputum, also called phlegm, contains white blood cells, dead cells, foreign debris that’s inhaled, bacteria and other immune cells. Computerized tomography (CT) scans take cross section images of the area around the heart and lungs to identify possible sources of acute respiratory distress syndrome. Heart Tests can rule out certain heart conditions that can be mistaken for ARDs. An electrocardiogram (ECG) test measures the heart’s rhythm and activity. An echocardiogram uses ultrasound to show if the heart muscle and valves are working correctly. Acute Respiratory Distress Syndrome (ARDS): Signs & Symptoms Acute Respiratory Distress Syndrome (ARDS): Treatment Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.