Few chief complaints in pediatrics are as common—or deceptively simple—as fever in children. Especially when that fever shows up in toddlers without a clear source.
We talk a lot about fever in infants under 3 months. And for good reason: there are detailed algorithms and evidence-based flowcharts for managing febrile infants. But once a child hits 3 months of age, the protocols fade, and things get a little murky. For kids aged 3 to 36 months, clinical decisions often depend on nuanced judgment.
Which is why I was so thankful for the chance to sit down and discuss this topic with Pediatric Infectious Disease specialist Dr. Eddie Lyon of Children’s Mercy Hospital in Kansas City. He walks us through a practical framework for making sense of this common dilemma.
First step in fever evaluation: sick or not sick?
The first step in evaluating a toddler with fever is the classic: sick vs. not sick. It sounds basic, but it's an advanced clinical skill. Vital signs matter, of course, but so does your observation: Are they interactive? Hydrated? Breathing comfortably?
In most well-appearing, immunized toddlers, serious bacterial infections are less common thanks to vaccines for Hib and pneumococcus. Still, invasive bacterial infections (IBIs) remain part of the differential diagnosis, and your clinical antennae need to stay alert.
Can't-Miss Diagnoses
Here are the infectious diagnoses you can’t afford to miss in a febrile toddler:
▪️Meningitis
▪️Bacteremia
▪️Pneumonia
▪️Retropharyngeal abscess
▪️Ostomyelitis or septic arthritis
▪️Urinary tract infection
Don’t forget to keep some non-infectious causes on your radar, such as:
▪️Kawasaki disease
▪️Oncologic processes like leukemia or lymphoma
▪️Autoimmune disorders like Lupus or Systemic Juvenile Idiopathic Arthritis (JIA)
Most Toddlers? It’s Viral
In most toddlers aged 3 to 36 months, fever without a source is due to viruses, so good old-fashioned supportive care is your best bet. Think roseola, adenovirus, enterovirus, EBV, or CMV. It can help to give the parents a heads up about the roseola rash, since that’s a diagnosis we can only make after the fever has resolved.
Remember that seasonal illnesses like influenza, RSV, or COVID-19 can show up without the typical respiratory symptoms. So it may be worth testing depending on the season and your patient’s risk of complications.
Red flags during a febrile child exam:
Keep yourself on the alert for any:
▪️Refusal to bear weight
▪️Pinpoint pain
▪️Neck stiffness
▪️Petechiae or purpura
▪️Unexplained lymphadenopathy
▪️Abnormal lung sounds
▪️New neurologic signs
Fever workup in children 3 to 36 months old: when to order tests
The key question for most clinicians is: “Do I need to do any tests?”
In well-appearing, vaccinated children with no red flags, you might do no workup or check a urinalysis. UTIs are a leading cause of fever without a source in females less than 2 years old and uncircumcised boys younger than 6 months. But the risk can depend on other factors, like how high the fever is and how long it’s been around. Use a UTI risk calculator when in doubt.
Consider COVID or flu testing during respiratory virus season. If a child has had 5 days of fever, start considering Kawasaki Disease—especially if they have mucosal changes, conjunctivitis, or extremity findings. In that case, CBC, CRP, ESR, LFTs, and BMP may help.
Routine blood cultures? Usually not helpful in vaccinated kids. But if the child is unvaccinated or immunocompromised, their risk for bacteremia goes up. So consider sending a blood culture for any child who is unvaccinated or immunocompromised.
What About Fever Management?
One of the most common questions we get in pediatric or urgent care settings is: “Should I treat the fever?”
Parents often worry about whether treating a fever will make the illness “last longer.” It helps to reassure them there’s no evidence for that. If the child is uncomfortable, treat it. If they’re playing and drinking despite a temp of 102°F, you can hold off.
Ibuprofen is often a favorite among pediatric clinicians. It lasts longer, and some studies show it reduces fever faster than acetaminophen. A 2024 study in Pediatrics showed better fever reduction with ibuprofen at 4 hours post-dose, though the effects were similar by 6 hours.
Alternating acetaminophen and ibuprofen? Totally fine if parents want to, especially with prolonged or high fevers. But you don’t need to recommend it routinely—it’s more important that parents dose correctly and monitor for effectiveness.
When to Reassess
If the fever lasts more than 5 days without a clear diagnosis, it's time to reassess. Return visits should also be prompted by new symptoms, worsening appearance, or evolving exam findings. Encourage caregivers to keep a fever diary—it helps both them and you.
Final Thoughts
Whether you’re working in primary care, the ED, or urgent care, managing fever in toddlers aged 3 to 36 months is one of the most common—and nuanced—tasks you do. Trust your clinical instincts, use your tools wisely, and remember: not all fevers need labs.
Clinical Takeaways:
▪️History and physical exam are your best tools in evaluating pediatric fever.
▪️Most febrile toddlers have viral infections. Stay alert for red flags.
▪️A UA is often the only test needed.
▪️Consider broader workups for unvaccinated or immunocompromised kids.
▪️Treat fevers if the child is uncomfortable. Ibuprofen may work slightly faster.
▪️Use your judgment, and don’t underestimate the power of a well-timed follow-up.
Need a quick refresher for your next shift? Check out our full conversation with Dr. Eddie Lyon on Peds Reviews and Perspectives podcast segment, "MOCA: Managing fever in children 3-36 months," for a deeper dive into managing fever without a source in 3 to 36-month-olds.