Yes, a pulmonary embolism (PE) can cause fever. Studies have found that anywhere from 14% to 50% of PE patients develop a fever, depending on how the temperature threshold is defined. The fever is typically low-grade, rarely climbing above 101°F (38.3°C), and it usually resolves on its own within a week.
How Common Is Fever With PE?
The numbers vary across studies because researchers use different temperature cutoffs. One study of 311 PE patients with no other explanation for their fever found that 14% had an elevated temperature. Other research using a lower threshold of 99.5°F (37.5°C) found fever in up to 50% of acute PE patients. The takeaway: fever is not the hallmark symptom of PE the way shortness of breath or chest pain is, but it’s far from rare.
In uncommon cases, fever can actually be the only symptom. A 2025 case series in The American Journal of Medicine described four patients who came to the emergency department with unexplained fever and no classic PE symptoms at all. Only after routine workups failed to find an infection did imaging reveal blood clots in the lungs.
Why PE Causes a Temperature Spike
When a blood clot lodges in the lung’s blood vessels, it damages tissue and triggers an inflammatory response. The body releases signaling molecules that raise your core temperature, the same basic process behind any inflammation-driven fever. If the clot cuts off blood flow long enough to cause a small area of lung tissue to die (called a pulmonary infarction), that dead tissue creates an even stronger inflammatory signal. The result is a low-grade fever that typically peaks the same day the clot arrives and tapers off over the following days.
What the Fever Typically Looks Like
PE-related fever follows a fairly predictable pattern. It tends to peak on the day the embolism occurs, stays in the low-grade range (under 101°F or 38.3°C in most cases), and gradually fades within about a week. High fevers above 102.2°F (39°C) can happen but are unusual. A fever that lasts longer than six days, or one that exceeds 101.3°F (38.5°C) and keeps climbing, should raise suspicion for something else, such as a secondary infection or pneumonia developing alongside the PE.
Fever Signals More Severe Clots
Fever with PE is not just an incidental nuisance. Research published in BMJ Open Respiratory Research found that PE patients who developed fever had significantly worse outcomes than those who stayed afebrile. Patients with fever were more likely to have massive or submassive clots (56% vs. 37%) and were nearly twice as likely to also have deep vein thrombosis in their legs (33% vs. 17%).
The clinical consequences were stark. About 70% of PE patients with fever needed intensive care, compared to 36% of those without fever. The need for mechanical ventilation was roughly five times higher (31% vs. 7%). In-hospital mortality was also elevated: 22% of febrile PE patients died during their hospitalization, compared to 10% of those without fever. Hospital stays averaged about 20 days for the fever group versus 12 days for the non-fever group.
This doesn’t mean that having a fever with PE guarantees a bad outcome. But it does suggest that fever can be a marker of a larger clot burden and a more dangerous situation overall.
How PE Fever Differs From Pneumonia
One of the biggest diagnostic traps with PE-related fever is that it can look like pneumonia. Both conditions cause shortness of breath, chest pain, and elevated temperature, and both can produce abnormal findings on a chest X-ray. A retrospective study spanning seven years found that 25 patients initially diagnosed with a lung infection actually had PE. The overlap in symptoms, including elevated inflammatory markers and visible lung infiltrates on imaging, had led clinicians down the wrong path.
There are patterns that help distinguish the two. Pneumonia typically presents with higher fevers, chills, productive cough, and much higher levels of inflammatory markers in the blood. PE more often starts with sudden-onset shortness of breath or sharp chest pain that worsens with breathing, and the fever tends to be milder. But these are tendencies, not rules. When fever is present alongside breathing difficulty and the cause isn’t obvious, imaging of the lung blood vessels (CT pulmonary angiography) is the definitive way to check for clots.
Fever Resolves Quickly With Treatment
Once anticoagulation therapy (blood thinners) is started for the PE itself, a fever caused purely by the clot typically breaks within 48 to 72 hours. In the case series from The American Journal of Medicine, all four patients whose unexplained fevers turned out to be PE became afebrile within three days of starting treatment. One patient’s fever resolved in just 48 hours.
This rapid response is actually useful diagnostically. If a fever persists well beyond 72 hours of appropriate anticoagulation, it suggests either an additional source of infection or a complication that needs further investigation. The speed of fever resolution can serve as a practical signal that the underlying PE is being effectively treated.