Cytokine Release Syndrome (CRS): Symptoms, Causes, Grading, Treatment and Outlook
Updated: 2 hours ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Quick answer
Cytokine release syndrome (CRS) is a flood of immune-system proteins called cytokines into the bloodstream, causing widespread inflammation that can damage organs. It most often follows cancer immunotherapy, especially CAR-T cell therapy and bispecific antibodies, and can also be triggered by infections or autoimmune diseases. Symptoms range from flu-like (fever, chills, fatigue) to life-threatening organ failure, and the condition can worsen quickly, so any fever after immunotherapy needs immediate medical care.
TL;DR
CRS occurs when an overreacting immune system releases excessive cytokines, producing fever, fatigue, body aches and, in severe cases, organ damage. It is graded 1 to 4, with higher grades more serious. Treatment includes corticosteroids and cytokine-targeting medications such as tocilizumab, siltuximab, and anakinra, and people with mild CRS after immunotherapy typically recover within one to two weeks.
What this guide can and cannot tell you: This guide is based on a single medically reviewed clinical source (Cleveland Clinic, updated July 14, 2025). It does not include prevalence or mortality figures, so none are given here. Timing and recovery ranges are typical, and your own course depends on the cause, the grade, and how quickly care begins.
What is cytokine release syndrome?
Cytokine release syndrome (CRS) is inflammation that happens when your immune system releases excessive amounts of cytokines into your bloodstream.
Cytokines are proteins that are part of a healthy immune system. They help control the growth and activity of your blood cells and immune cells. But a flood of cytokines may cause widespread inflammation.
This can lead to serious and sometimes life-threatening conditions, including organ failure. Excessive amounts of cytokines cause widespread inflammation that damages organs and tissues. CRS may happen after immunotherapy (see our guide to immunotherapy for breast cancer for one example of how these treatments work). Other causes are bacterial and viral infections or autoimmune diseases.
Cytokine release syndrome falls under the medical condition cytokine storm. A related overreaction of the immune system to infection is described in our guide to sepsis.
What are the symptoms of cytokine release syndrome?
Cytokine release syndrome symptoms can be mild. You may feel like you have the flu. But the syndrome may affect different areas of your body.
Symptom | Description |
Chills and high fever | Fever with chills, often the first sign |
Confusion and dizziness | Mental changes and lightheadedness |
Diarrhea | Gastrointestinal involvement |
Difficulty swallowing | Throat or esophageal involvement |
Headaches | Common in mild cases |
Joint and muscle pain | Body aches, similar to flu |
Nausea and vomiting | Gastrointestinal symptoms |
Skin rash | Skin involvement |
Tiredness | Fatigue |
Because symptoms can resemble the flu, people receiving immunotherapy must stay alert and report any fever promptly.
What causes cytokine release syndrome?
The syndrome happens when your immune system overreacts and releases large amounts of cytokines.
Immunotherapy for cancer, particularly CAR-T cell therapy and bispecific antibodies, is the most common trigger. CRS may also happen due to bacterial and viral infections or autoimmune diseases.
What increases the risk?
Having an autoimmune disease or certain genetic conditions that affect your immune system may increase your risk. Hemophagocytic lymphohistiocytosis (HLH) is an example of a genetic condition that can lead to cytokine release syndrome.
What are the complications of cytokine release syndrome?
Cytokine release syndrome can cause severe inflammation in your kidneys, liver, or lungs. It may also damage your blood vessels or heart. Without prompt treatment, CRS may cause serious medical issues. Some may be life-threatening.
Life-threatening complication | What it involves |
Capillary leak syndrome | Fluid escapes from tiny blood vessels into tissues |
Cardiomyopathy and heart failure | Heart muscle damage and weakened pumping |
Kidney failure | Loss of kidney function |
Liver failure | Loss of liver function |
Lung failure and very low oxygen levels (hypoxemia) | Severe breathing impairment |
How is cytokine release syndrome diagnosed?
Healthcare providers diagnose CRS in different ways depending on the cause.
If you receive immunotherapy, your provider will watch for CRS symptoms. Those symptoms may show up within 24 hours or up to two weeks after your treatment. If you develop symptoms, your provider may do tests including a complete blood count (CBC), cytokine levels, C-reactive protein test and other tests to check inflammation levels, and kidney and liver function tests.
How is CRS graded?
Cytokine release syndrome grades range from 1 to 4. The higher the number, the more serious the condition. Your healthcare provider will consider the following issues to establish a grade.
Grading factor | What it indicates |
High fever, low blood pressure, or fast heartbeat | Vital-sign instability at lower grades |
Steps needed to keep vital signs stable | More aggressive supportive care required |
Need for mechanical ventilation | Higher-grade severity |
Organ failure symptoms (weakness, fast shallow breathing) | Grade 4, the most serious |
How is cytokine release syndrome treated?
Your treatment will vary depending on the reason why you have CRS. Treatment for severe CRS from immunotherapy may include:
Treatment | What it does |
Corticosteroids | Reduce inflammation |
Cytokine-targeting medications | Block specific cytokines: siltuximab (Sylvant), tocilizumab (Actemra), and anakinra (Kineret) |
Medication for very low blood pressure | Supports stable blood pressure |
Mechanical ventilation | Supports breathing in severe cases |
How long does recovery take?
Your recovery time depends on your situation. People with mild CRS symptoms after immunotherapy usually recover within one to two weeks. Your recovery may take longer if an infection causes CRS. You may feel better within a few days after treatment for mild CRS symptoms from immunotherapy, while it will take longer to recover from severe CRS.
When should I seek care?
Contact your healthcare provider if immunotherapy causes a fever or other CRS symptoms. The condition can worsen quickly, which increases your risk of life-threatening complications. It's important that you get medical care right away.
A note from the clinical source: "A cytokine release syndrome (CRS) diagnosis may make you anxious because it can cause serious or life-threatening complications. You may feel frustrated having to cope with another medical issue when you're already trying to manage cancer or cancer treatment. Your healthcare team understands these feelings. They'll explain symptoms that may mean you're developing CRS. Knowing what to look for may help you feel less anxious. So will knowing that your providers are keeping a very close eye on you and your health. Don't hesitate to share any concerns about changes in your body. Early diagnosis and treatment can help keep CRS from becoming a serious medical issue."
What is the outlook for cytokine release syndrome?
What you can expect if you have CRS depends on the cause and your symptoms. For example, you may feel better within a few days after treatment for mild CRS symptoms from immunotherapy. It will take longer to recover from severe CRS.
Conclusion: knowing what to watch for makes all the difference
Cytokine release syndrome is a serious immune reaction in which a flood of cytokines causes widespread inflammation that can damage organs and, in severe cases, become life-threatening. It most often follows cancer immunotherapy, particularly CAR-T cell therapy and bispecific antibodies, and symptoms can appear anywhere from 24 hours to two weeks after treatment. (For broader background on the disease itself, see our complete guide to cancer.)
The essentials are simple but critical: expect your care team to monitor you closely after immunotherapy, treat any fever as urgent, and report symptoms like chills, confusion, rashes, or difficulty breathing right away. When caught early, CRS is treatable with corticosteroids and cytokine-targeting medications, and people with mild cases typically recover within one to two weeks.
Your next step: If you are scheduled for or recovering from cancer immunotherapy, review the warning signs with your care team before treatment begins. If you develop a fever or any CRS symptoms, contact your healthcare provider immediately. The condition can worsen quickly.
Frequently asked questions
What is cytokine release syndrome?
Cytokine release syndrome (CRS) is inflammation that happens when your immune system releases excessive amounts of cytokines into your bloodstream, causing widespread inflammation that can damage organs and tissues.
What are cytokines?
Cytokines are proteins that are part of a healthy immune system. They help control the growth and activity of your blood cells and immune cells.
Is cytokine release syndrome the same as cytokine storm?
CRS falls under the medical condition called cytokine storm, a broader category of excessive cytokine-driven inflammation.
What causes cytokine release syndrome?
It happens when your immune system overreacts and releases large amounts of cytokines. Immunotherapy for cancer, particularly CAR-T cell therapy and bispecific antibodies, is the most common trigger. Bacterial and viral infections and autoimmune diseases can also cause it.
When do CRS symptoms start after immunotherapy?
Symptoms may show up within 24 hours or up to two weeks after treatment.
What do CRS symptoms feel like?
Symptoms can be mild, like the flu, and include chills and high fever, confusion and dizziness, diarrhea, difficulty swallowing, headaches, joint and muscle pain, nausea and vomiting, skin rash, and tiredness.
Why does CRS feel like the flu?
The widespread inflammation produces fever, body aches, and fatigue, symptoms similar to a flu infection.
Is cytokine release syndrome life-threatening?
Without prompt treatment, CRS may cause serious medical issues, some of which may be life-threatening, including organ failure.
What complications can CRS cause?
Severe inflammation can affect the kidneys, liver, or lungs, and may damage blood vessels or the heart. Life-threatening complications include capillary leak syndrome, cardiomyopathy and heart failure, kidney failure, liver failure, and lung failure with very low oxygen levels.
Who is at higher risk for CRS?
People with an autoimmune disease or certain genetic conditions that affect the immune system have increased risk. Hemophagocytic lymphohistiocytosis (HLH) is an example of a genetic condition that can lead to CRS.
How is CRS diagnosed?
Providers use a complete blood count (CBC), cytokine level tests, C-reactive protein and other inflammation tests, and kidney and liver function tests. After immunotherapy, providers watch closely for symptoms.
What tests check for cytokine release syndrome?
Cytokine levels, C-reactive protein (CRP) test, complete blood count, and kidney and liver function tests.
How is CRS graded?
CRS grades range from 1 to 4, and the higher the number, the more serious the condition. Grading considers fever and vital signs, steps needed to stabilize vital signs, need for mechanical ventilation, and organ failure symptoms.
What does Grade 4 CRS mean?
Grade 4 is the most serious, involving organ failure symptoms such as weakness and fast, shallow breathing.
How is CRS treated?
Treatment depends on the cause. Severe CRS from immunotherapy may be treated with corticosteroids, cytokine-targeting medications (siltuximab, tocilizumab, anakinra), medication for very low blood pressure, and mechanical ventilation.
What medication stops cytokine release syndrome?
Medications that target specific cytokines, siltuximab (Sylvant), tocilizumab (Actemra), and anakinra (Kineret), block the cytokines driving the syndrome. Corticosteroids reduce inflammation.
When is mechanical ventilation needed for CRS?
Mechanical ventilation may be required in severe CRS when the patient cannot breathe adequately on their own, and it factors into higher CRS grades.
How long does it take to recover from CRS?
People with mild CRS symptoms after immunotherapy usually recover within one to two weeks. Recovery may take longer if an infection causes CRS, and severe CRS takes longer to recover from than mild cases.
Can you recover fully from cytokine release syndrome?
Many people feel better within a few days after treatment for mild CRS. Early diagnosis and treatment can help keep CRS from becoming a serious medical issue, though outcomes depend on the cause, grade, and how quickly care begins.
What should I do if I have a fever after CAR-T cell therapy?
Contact your healthcare provider immediately. The condition can worsen quickly, and getting medical care right away is important to prevent life-threatening complications.
Is CRS always caused by cancer treatment?
No. While cancer immunotherapy (especially CAR-T and bispecific antibodies) is the most common trigger, bacterial and viral infections and autoimmune diseases can also cause CRS.
Does CRS happen with all immunotherapy?
Not with all immunotherapy, but CRS is especially associated with CAR-T cell therapy and bispecific antibody treatment. Your provider will explain your specific risk.
How will I know if I'm developing CRS?
Your healthcare team will explain the symptoms to watch for. Knowing what to look for helps reduce anxiety, and providers keep a very close eye on your health after immunotherapy.
What does it mean if my oxygen levels drop with CRS?
Very low oxygen levels (hypoxemia) and lung failure are among the most serious complications, often requiring mechanical ventilation and immediate treatment.
Can autoimmune disease cause cytokine release syndrome?
Yes. Autoimmune diseases and autoimmune disease-related conditions can trigger CRS, and having an autoimmune disease increases risk.
External references
Cleveland Clinic: Cytokine Release Syndrome (CRS) (primary source, medically reviewed, last updated July 14, 2025)
References
Disclaimer: This article is for general educational purposes only and does not constitute medical advice. It is based on a single referenced clinical source and should not replace professional diagnosis or treatment. If you are receiving immunotherapy and develop a fever or other CRS symptoms, contact your healthcare provider immediately. The condition can worsen quickly.
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