Q: The flu test was negative, but the fever has returned. Could it still be the flu and should we retest?
- Myeongchan Kim
- 10 hours ago
- 2 min read
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 started having a fever at 3:30 PM yesterday. We went to the clinic around 7:00 PM, and a flu test came back negative. The fever returned during the night, so I gave them a fever reducer, which brought the temperature down. They were fever-free during the day today, but the fever is starting to rise again right now. Is it possible that it is still the flu? Should we get tested again?
Answer:
I completely understand your concern. It is actually quite common to get a false-negative result on a flu test during the very early stages of the illness.
Flu Test Timing & Accuracy
Within 12 to 24 hours of symptom onset: 30-50% accuracy.
After 24 to 48 hours: 80-90% accuracy.
The virus needs enough time to multiply in the body for the swab test to detect it.
Evaluating the Current Situation
Since the fever started at 3:30 PM yesterday and the test was performed just a few hours later at 7:00 PM, it is very likely that the test was done too early. A fluctuating fever pattern—where the temperature goes up and down—is a typical symptom of both the flu and the common cold.
When to Consider Retesting
At least 48 hours after the symptoms first began.
If a high fever persists and is accompanied by worsening symptoms like severe muscle aches, headaches, or a harsh cough.
If another family member is officially diagnosed with the flu.
What You Should Do Now
Administer fever reducers regularly (every 4-6 hours) as needed to keep your child comfortable.
Encourage plenty of fluids to prevent dehydration.
Keep a log of their symptoms, noting the fever pattern and any new signs of illness.
⚠️ When to Visit a Doctor Immediately
Please seek immediate medical evaluation if your child experiences any of the following:
Difficulty breathing or chest pain.
A high fever that lasts for more than 3 days.
Signs of dehydration, such as a significant decrease in urine output or no tears when crying.
Whether it is the flu or another respiratory virus, the initial supportive care and management are exactly the same. Continue to monitor your child's symptoms closely, and consult your pediatrician tomorrow to determine if another in-person evaluation or a retest is necessary.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
