Q: My child tested negative for the flu, but the fever is rising. Should we test again?
- Myeongchan Kim, MD
- Jun 10
- 2 min read
Updated: Jul 8
Medically reviewed by Sang Hyun Ahn, MD
Content edited by Myeongchan Kim, MD
This post is a dramatization of a question and answer session experienced by our actual medical reviewers. Please note that this content is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
Question:
My child developed a fever of 38.3°C on Saturday morning. Knowing that immediate testing might not be accurate, we waited and got a flu test on Sunday afternoon (about 32 hours after symptoms started). The result was negative. The doctor mentioned a mild cough, some phlegm, and a slightly swollen throat, and prescribed symptom-relief medications and fever reducers.
However, today is Monday, and the fever is getting worse. It fluctuates but has gone up to 38.8°C, so we are alternating two types of fever reducers. Since the first test was done 32 hours after symptoms appeared, is it possible for a retest to come back positive now? Can a flu test be negative at first and then turn positive later?
Answer:
It is completely understandable that you are worried, as your child's fever continues to rise despite the initial negative test.
Regarding the timing and the need for a retest: Testing 32 hours after the onset of symptoms is generally an appropriate timeframe. However, while relatively uncommon, it is possible for an initial negative result to later turn positive. This can occur (acting as a false negative) especially during the early stages of the illness or if the viral load was too low to be detected at the time of the swab. If the fever continues to rise and persists into the third day, a retest is certainly worth considering.
The fact that the fever has climbed to 38.8°C and persisted from Saturday to Monday requires careful observation.
Seek immediate medical attention if your child shows any of the following signs:
Difficulty breathing or chest pain
Severe dehydration (e.g., not urinating for more than 8 hours)
Decreased consciousness, extreme lethargy, or unusually slow responses
New rashes or changes in the color of the lips or nail beds (such as a bluish or pale tint)
Even if it is not the flu, the ongoing fever could be caused by a different viral infection or a secondary complication such as pneumonia. Because the high fever has persisted for three days and the symptoms are worsening, a medical re-evaluation is necessary.
When you revisit the clinic, please inform the doctor about:
The exact fever pattern (peak temperatures and how well the fever responds to the medications).
Your interest in potentially retesting for the flu.
The need to check for other viral infections or secondary bacterial infections like pneumonia.
Please consult your pediatrician promptly for a thorough in-person assessment and proper guidance.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
