Dr. Jon Hallberg: When to be concerned about a fever

It's not unusual for children to develop a fever. But many parents are unsure at what point they should seek treatment.

MPR's medical analyst Dr. Jon Hallberg discussed all things fever with Tom Crann of MPR News Tuesday. Hallberg is a physician in family medicine at the University of Minnesota and medical director of the Mill City Clinic.

An edited transcript of that interview is below.

Dr. Jon Hallberg: It really varies on the age of the child or the adult. It can even vary in time of day. We all agree that a fever starts somewhere around 100.4 [degrees Fahrenheit]. If you've got a little kid at home, a baby, an infant that's less than three months of age, you've really got to take that seriously and figure that out. Most of the time though, we don't really need to worry about it as much.

Tom Crann: What's actually going on in the body with fever?

Hallberg: It's really a fascinating cascade of events that's occurring.

Let's say you've been exposed to a virus or a bacteria. There are certain interactions going on with white blood cells, part of the immune system. Proteins, little markers, are sent through the bloodstream and they're picked up by a part of the brain called a hypothalamus, which is sort of the thermostat of the brain. It increases the set point; it turns on the thermostat, so your body goes from being 98.6 degrees to 102 or 103 [degrees Fahrenheit].

Crann: More common in children or adults?

Hallberg: We probably see it more in kids, frankly it's probably because kids are getting exposed to viruses and bacteria for the first time in their lives. A lot of us who have made it through childhood, we don't mount the same response because we've seen those microbes before.

Crann: How dangerous can a fever be at its worst?

Hallberg: There's actually some debate about fevers, are they good or are they bad? On the good side, they might be doing something to slow down the growth and the reproduction of viruses and bacteria.

On the bad side, we've all seen it in our kids, people look pretty miserable. The higher the fever, the worse you feel.

It's not until it gets to 106 [degrees Fahrenheit] or so that it gets dangerous, but again, if you have a little kid, an infant with a fever, it doesn't need to be that high to be potentially serious.

Crann: At what point and how to we start to treat a fever?

Hallberg: That's also debatable. You don't have to treat a fever. I think as parents we always feel obligated to treat because we want to do something. I think kids are going to look pretty uncomfortable if it's 102, 103 [degrees] or higher, and the big issue is that if it's going on and not just self-limited, stopping on its own, we need to be looking for a cause. Again, this is really true with little kids and infants. The longer it persists, the higher the fever. We've got to figure out why it's happening.

Crann: What don't parents know about fever that you as a doctor wish they did?

Hallberg: People often think that fever in and of itself is sort of a disease. It's not. It's just a physiologic response to exposure to something. And also it can happen if it's really hot outside. Once it gets to 95 Fahrenheit, the body has a very hard time cooling itself, so the temperature can rise.

The bottom line is that typically there's a reason it's happening. It's often something benign like a virus that's going to burn itself out pretty quickly. It doesn't have to be treated.

And people often feel, 'Tylenol is not working, now what do I do?' And they can switch to something else like Ibuprofen. Again, it's more watching, being reassured, and if it persists and it's high, figure out what's going on.

Crann: Is there a bottom line here, a temperature at which you should bring the child to the doctor?

Hallberg: Everyone pretty much agrees that if you have a child who is three months old or less, 100.4 [degrees] is the point at which you really need to investigate and do a workup. Beyond that, I think that most parents are going to be pretty uncomfortable with their kids at 102, 103, 104 [degrees].

It's not just the temperature, it's what does the kid look like. If they're running around and they look great, it's not such a big deal. But if it's a kid who's not eating, burning up, looking really uncomfortable, not very active, that needs and warrants a workup.

Interview transcribed and edited by Jon Collins, MPR reporter.

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