What counts as a fever during chemotherapy?

During chemotherapy, a fever is a temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher. The CDC calls a fever during chemotherapy a medical emergency and says to call your doctor immediately at that temperature.

Here is what each source says, in its own words:

• CDC, writing for people getting chemotherapy: "Call your doctor immediately if you have a temperature of 100.4ºF (38ºC) or higher."
• American Cancer Society: "For people with cancer, a fever is defined as a temperature of 100.4℉ (38℃) or higher."
• National Cancer Institute: lists a "fever of 100.5 °F (38 °C) or higher" as a sign of infection to report to your health care team. This site uses the lower, more cautious CDC figure of 100.4 °F (38 °C).

The numbers differ by a tenth of a degree because 38.0 degrees Celsius converts to 100.4 degrees Fahrenheit, and NCI's 100.5 is a rounding of that same reading.

Your own team may give you a number of their own. The American Cancer Society says: "Ask your cancer care team what temperature they consider to be a fever. It might be different depending on your situation, but 100.4°F (38°C) is often used." If your temperature is close to the number and you are not sure, call. Care teams would rather hear from you early.

This matters because some cancers and treatments like chemotherapy lower your white blood cells, the cells that fight infection, so an infection can become serious quickly. Other signs of infection include chills, cough or sore throat, diarrhea, and redness or swelling where a catheter enters the body.

The CDC says a fever during chemotherapy might be an infection, which is life-threatening and needs to be seen quickly. If you cannot reach your team, go to the nearest emergency department or call 911. The CDC says to tell the person checking you in that you are a cancer patient having chemotherapy.