Fever during cancer treatment: When to seek care

We often warn our cancer patients here at UT MD Anderson to alert their care teams if they develop a fever.

But how high does your body temperature have to go in order to qualify as one? What’s the difference between a low-grade fever and a high-grade fever? And, when should you start to worry?

Here’s what to know about fevers, including when to seek help and why the rules are different for cancer patients.

What body temperature is considered a fever?

By definition, a fever in humans is any body temperature above 100.4 degrees Fahrenheit. But what constitutes a fever can actually vary from person to person.

That’s because the average human body temperature is about 98.6 degrees. But the range of normal human body temperatures is between 97.0 and 99.0 degrees. So, if you naturally run a little lower than average, 99.5 might feel like a low-grade fever.

What’s the difference between a low-grade fever and a high-grade fever?

Anything less than 101.5 degrees is considered a low-grade fever. Anything above that is considered a high-grade fever.

But people typically differentiate between the two based on how they feel.

With low-grade fevers, you might not feel too bad. Just a little tired or run down. Once you get above 102, though, you start experiencing additional symptoms, like:

• Flushed skin
• Headaches
• Lethargy
• Muscle aches
• Rigors (the shaking/shivering that can come with chills)

Some people describe a high fever as feeling like they’re walking through wet cement. Even something as simple as lifting their head off a pillow or sitting up in bed takes incredible effort.

What’s the most effective way to measure body temperature?

Oral and axillary (armpit) thermometers are probably the most accurate. But forehead thermometers are the easiest and most convenient.

Just keep in mind that forehead thermometers can be affected by your environment. So, if you’re in bed and covered up with a lot of blankets, for instance, your reading might be artificially high. But if you’re in a cold room and dressed in very thin clothing, your reading might be artificially low.

When should you worry about a fever?

That actually varies, too, depending on your situation.

Certain conditions are known to cause a fever, so it’s expected and therefore nothing alarming. If you have the flu and a temperature of 101F, for instance, we’ll probably just focus on managing your symptoms, assuming you’re otherwise healthy. We’ll likely tell you to take some acetaminophen, and let us know if the fever doesn’t resolve on its own.

But if you’re a cancer patient, our rule of thumb is to seek medical attention immediately for any fever above 100.4F. That means going to an emergency room ASAP, whether it’s ours here at UT MD Anderson or the one nearest you.

If you’re immunocompromised and have an infection, we need to get you started on IV antibiotics right away. Time is of the essence in those situations, because your condition can deteriorate very rapidly. We don’t want you going into sepsis.

You should also call a doctor immediately if you have fever of 104.0 or higher, regardless of your situation. Once your temperature reaches a certain point, the proteins in your body start to harden, so they don’t work as well anymore. Your blood pressure can begin fluctuating, and other body systems may start shutting down.

Any temperature above 106 degrees is considered incompatible with human life. The protein in your body will start solidifying at that point, like a fried egg. So, you need to get it down, and fast.

You also should seek help immediately if you develop a rash, have trouble breathing or start vomiting when you have a high temperature.

What’s the quickest way to reduce a fever?

Over-the counter medications like acetaminophen and ibuprofen are probably the fastest, but cooling blankets and cold pads also work. They just take a little longer to be effective.

If you can’t take NSAIDs (aspirin, ibuprofen, naproxen, etc.) due to kidney dysfunction, stomach ulcers/acid reflux or low blood counts, we might use steroids. In really urgent situations, you may need to consider an ice bath.

Is it ever better to let a fever go untreated (i.e. to “burn out” or kill an infection)?

In this day and age, I would say no.

Fevers are a wonderful protective mechanism. In the days before antibiotics, they were the body’s best way of fighting an infection. Unfortunately, they’re not always effective. And, if left untreated, both high fevers and infections can lead to other issues, such as dehydration, seizures, organ failure, and even death.

With all the resources we have available today, it’s just not necessary to let a fever go unchecked, especially if it’s making you uncomfortable.

Is fever ever a symptom of cancer itself?

Yes. It can sometimes be a symptom of certain cancers such as lymphoma. Unexplained fevers are something we typically look for with that disease.

Fevers can also be the result of some solid tumors, because they prompt the body to release the same cytokine proteins that activate the immune system against infections. Usually, fever is not a presenting symptom with those, though, so the cancer would need to be pretty advanced to see that.

Tejo Musunuru, M.D., is a general oncologist at UT MD Anderson. 

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