How Immune Pneumonitis Is Diagnosed — The Scans, Tests and Timeline Explained

Getting tested for suspected immune pneumonitis is never something to postpone — report any new or worsening cough, breathlessness, or chest tightness the same day it appears. If breathlessness is severe or sudden, treat it as an emergency, not a symptom to schedule around.

A high-resolution CT scan of the chest is the primary test used to diagnose immune-related pneumonitis. It's arranged urgently once symptoms are reported and is usually completed the same day, since NCCN and ASCO irAE guidance treats new respiratory symptoms on immunotherapy as time-sensitive.

The CT looks for patterns of inflammation across the lung tissue and gives your oncology team something concrete to compare against your recent cancer-monitoring scans, which is how disease progression is ruled out rather than assumed. It's arranged urgently, coordinated between your oncologist and a radiology partner, with a pulmonologist involved if the picture needs a specialist read. Alongside the CT, a pulse oximeter check is done immediately, and a swab or sputum sample is usually sent the same visit to check for infection in parallel — the two possibilities are investigated together, not one at a time.

No, not for every case. Bronchoscopy is used selectively — mainly when the CT and clinical picture aren't clear enough on their own, when infection needs to be ruled out more definitively, or when symptoms are moderate to severe rather than mild.

During the procedure, a thin scope is passed into the airways under sedation to collect a fluid sample and, occasionally, a small tissue sample — helping your team distinguish pneumonitis from infection or another lung condition when the CT alone leaves genuine uncertainty. Many milder, typical presentations are diagnosed and treated from the CT and clinical assessment alone, without this additional step; it's an option reached for when the picture calls for it, not a routine part of every workup.

Pulse oximetry and basic blood tests come back the same day, and a CT chest is usually read and reported within the same day to 24 hours given how urgently these scans are prioritised. Swab or sputum results for infection typically take 24 to 48 hours to fully return.

Onset, typically: pneumonitis most often prompts this workup 8–24 weeks after starting immunotherapy, though it can appear after a single dose or, less commonly, months after treatment ends — one reason results are prioritised over a routine queue. Your team usually acts on the CT and clinical picture without waiting for every test, so treatment isn't held up by one pending result. There is no safe home-management step while results are awaited — complete the workup the same day it's started, or go to the ER for the emergency signs above.

Once reported, the workup follows a structured sequence rather than one test in isolation — infection and disease progression are checked alongside pneumonitis from the start.

1. 1

   Same-day oxygen check and grading

   A pulse oximeter reading and a clinical review grade how the symptom is affecting daily activity — mild, moderate, or severe — following the immune-related adverse event grading referenced in NCCN and ASCO guidance.

2. 2

   Urgent CT scan of the chest

   Arranged the same day, the CT identifies inflammation patterns in the lung tissue and is compared against your baseline cancer-monitoring scans to check for disease progression alongside pneumonitis.

3. 3

   Ruling out infection in parallel

   A swab or sputum sample, and sometimes blood markers, are sent at the same visit — because a chest infection needs antibiotics, not the steroid treatment pneumonitis needs, and both are checked together rather than sequentially.

4. 4

   Bronchoscopy, if the picture is unclear

   When the CT and clinical findings don't give a confident answer, or symptoms are more severe, bronchoscopy with a fluid sample adds detail that imaging alone can't provide.

5. 5

   Diagnosis, steroids, and monitoring for restart

   Once confirmed, steroid treatment usually starts promptly and immunotherapy is paused while your lungs recover; your tumour board then reviews follow-up scans and your response before deciding whether, and when, treatment can safely resume.

No single symptom separates the three — that's why the workup checks all of them together, with the CT pattern, infection tests, and comparison against your own prior scans each ruling things in or out.

These companion pages go deeper into specific parts of the same lung and breathing irAE pathway — worth reading alongside this one.

• Treatment for Immune Pneumonitis and How Long Recovery Takes — what happens after diagnosis, from steroids through to restarting immunotherapy.
• Immunotherapy When You Already Have COPD or Fibrosis — how an existing lung condition changes monitoring and how pneumonitis is told apart from your baseline symptoms.
• Using a Home Pulse Oximeter During Immunotherapy — what an oxygen reading can and can't tell you between visits.
• Immunotherapy at CION Cancer Clinics — how we monitor and support patients through immune-related side effects, from the first infusion onward.

A Fast, Clear Workup Reduces Uncertainty

Patients who report breathing symptoms promptly are supported by the same multidisciplinary team throughout testing and treatment.