Q: Was the flu test done too early at 16 hours? My child's fever spiked to 39°C after a negative flu test. Should we re-test?
- Myeongchan Kim
- 3 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 experiencing a fever and stomachache yesterday evening, so we visited the pediatric clinic this morning. They have no vomiting or diarrhea at all. Just in case, a flu test was done, which came back negative, so we returned home with only stomach medicine and fever reducers. At the hospital, the fever was mild, around 37.5°C, but since coming home, it has spiked to 39°C. My child says their stomach no longer hurts.
The flu test was conducted about 16 hours after the symptoms first appeared. Was the test done too early? If the fever continues to rise, I would like to know if we should do another flu test tomorrow.
Answer:
I understand how worrying it can be to see your child struggling with a high fever.
Regarding your question about the timing of the flu test, your suspicion is correct. At 16 hours after symptom onset, the viral load may not be high enough to be detected. Usually, testing 24 to 48 hours after symptoms begin provides a much more accurate result.
Based on the current situation:
• A high fever of 39°C with an improving stomachache indicates a possible flu infection.
• The absence of vomiting and diarrhea suggests this is not a typical case of enteritis (stomach flu).
• The fever rising after the hospital visit shows that the illness is currently progressing.
Immediate steps to take at home:
Administer fever reducers: Give an appropriate dose based on your child's weight every 4 to 6 hours.
Encourage hydration: Offer water or electrolyte drinks frequently in small amounts to prevent dehydration.
Keep them comfortable: Dress your child in light clothing and maintain a comfortably cool room environment.
We strongly recommend a re-test for the flu tomorrow if:
• The fever consistently remains above 38.5°C.
• Respiratory symptoms like a cough, runny nose, or severe body aches begin.
• Your child has been exposed to anyone diagnosed with the flu recently.
Seek emergency medical care immediately if you notice:
• Difficulty breathing or chest pain.
• Decreased consciousness, extreme lethargy, or inability to wake up.
• Signs of severe dehydration (no tears, no urine for several hours).
• Seizures.
Since early treatment is crucial for the flu (antiviral medications like Tamiflu are most effective when started within 48 hours of symptom onset), it is highly recommended to visit your pediatrician for a re-test tomorrow morning if the high fever and symptoms persist. Please ensure your child rests well tonight and follow up with a doctor in person for a proper clinical evaluation.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
