Diagnosis using fever, and fever reducing drugs

Factual Questions
1

Fever is an important diagnostic tool. Supposedly, aspirin and ibuprofen and naproxen and other drugs can reduce or eliminate fever.

Why isn’t it important, when using fever to diagnose illness, to consider whether the patient has taken fever reducing drugs, and how much and how recently?

Whenever I’m asked about fever, I usually point out whether I’ve taken fever reducing drugs and how much and how recently. Nurses and doctors and other medical folks never make a note of this, near as I can tell. If I don’t offer the information, they never ask. I’ve asked a couple of people why the information wouldn’t be important, and they seem (to me) to blow off the question, something like “Well I guess maybe it could matter but we really don’t use it” or something like that.

So - what good is information about fever, if the drugs that influence it are not noted?

2

Interesting question - I’m posting here partly to see what others say.

I do know that guidelines for a child returning to school after an illness often include “no fever for 24 hours” and also state that this has to be “without fever-reducing meds”. In other words, Junior has to be med-free and still fever-free for 24 hours, no dosing him with Tylenol round the clock so you can send him back to school before the fever is truly gone.

3

>…state that this has to be “without fever-reducing meds”…

Well, thank you. That’s interesting, and it’s the first thing I’ve ever heard anybody else say that addresses the point!

4

This happened to me very recently, when I had pneumonia and bronchitis. Before seeing the doctor, I was pre-examed by a nurse, who took my temperature but didn’t care about aspirin I had taken. The doctor, however, did ask me about it.

5

You’re right, fever is important in diagnosis.
Examples 1: When seeing someone in clinic who presents with a fever we ask what they’ve been taking for the fever and whether Tylenol/whatever has been sufficient to control it. If you’re taking Tylenol every 4 hours and still have a fever of 103 I’m more concerned than if you present with sniffles and a mild fever that is adequately controlled with Tylenol.
Example 2: When I’ve had hospitalized patients with post-surgical infection we tracked how frequently they are requiring acetaminophen to control symptoms and when planning discharge we generally wanted them to have been afebrile for at least 24 hours.

IANAD. I am a med student doing clinical rotations.

6

My “fever” and your “fever” might not be the same things.
I don’t get excited until it’s over 38 degrees celsius (100.4 F). At that point I’ll take blood cultures and worry about you. Anything under that level gets paracetamol (acteominophen) only.

If you’re afebrile and you took antipyretics recently, well, good for you, they’re working and you aren’t that sick.

If your temp is mildly elevated (say 37.6) and you took antipyretics, I’ll just make sure you get some more when you’re due them and keep an eye on you.

If you’re really sick, no anti-pyretic in the world is going to get your temp down to normal. If it’s over 38 degrees C and you’ve taken an antipyretic…I’m more worried than if you hadn’t, but I don’t do anything differently.

If it’s over 38 degrees C and you haven’t taken an antipyretic, you get blood cultures, I worry about you and you’ll also get an antipyretic.

Usually they don’t ask because it doesn’t matter… your temp is high, you get blood cultures and an anti-pyretic, it isn’t, you don’t. If you’ve taken an antipyretic more than 4 hours ago, it doesn’t matter anyway.

Temps under 38 are not going to do you any harm, you’ll probably get a fan and a cool washcloth, but not too much else in the way of specific treatment for the fever itself if you’ve already had your antipyretic.

Paracetamol is only of the weakest painkillers, most hospital inpatients are written up for it QID for pain, if they’re still spiking temps with that, they’re not going home, even if the pain is controlled. Fevers are signs of infection (usually).

Whether that is a bacterial infection, requiring antibiotics, or a viral infection, requiring supportive treatment only, has nothing to do with how high your fever is, and everything to do with how sick you are and the source of the infection.

7

Our kid’s preschool had the same rule. I’m guessing it’s pretty standard.

8

Well, this is all interesting. I still don’t have a good sense of why standard practice works well.

I take 6 Naproxen tablets a day, 1320 mg, for arthritis. Meanwhile, I have chronic bronchitis and often get bacterial infections, for which I keep Levaquin on hand, and start a 10 day treatment of 750 mg once per day, if the combination of cough and phlegm and feeling feverish and measured temperature suggest infection. The Levaquin often gets extended out to 20 days or even more, if stopping it brings symptoms back quickly. This whole setup has been worked out and adjusted over the last 20 years with my pulmonologist, whom I just saw an hour ago, but who will of course be nominally unavailable for the next three days of holiday weekend.

So, I see the role that temperature measurement plays, but I also see the Naproxen probably influences it, and since I’m not starting and stopping Naproxen to try to bring the fever down but rather taking it year round for another problem, I still am guessing it is a poorly characterized source of error in this whole process. I’d like to find a good thorough analysis of this somewhere, including a list of what temperature you would have had without meds, given that you took so much of a given drug and then measure a given temperature. A correction chart for the influence of meds, that’s what I’d like to find.

But, I have Dr’s orders to follow, correction chart or not.

9

You won’t find such a thing.

All human beings fluctuate their body temperature from minute to minute, so that even if your temp measure 36.8 now, it could be 37.1 in two hours.

Likewise, antipyretics don’t work the same for everyone, and while they will not reduce a temp of 39 to a temp of 36, exactly how well they work depends on the person, their normal temp and the particular illness they have.