A body temperature above 36.5°C-37.5°C. Generally the higher it is the worse. Above 42°C you are pretty much dead.
Everyone has had a fever at some point. Even the Queen. It is an excellent diagnostic indicator for someone being unwell.
Its an interesting one. Basically, chemicals called pyrogens make the hypothalamus raise the body temperature. Sometimes these chemicals are on the cell walls of bacteria, sometimes the immune system releases them.
The reason you get shivers and feel cold is that the pyrogens make the hypothalamus think that the correct temperature to aim for is higher, say 38.5°C. Even though you are at 37°C, which is normal, your body now thinks it is 1.5°C too cold. So it starts shivering, vasoconstricting and feeling chilly, aiming for that new temperature. When the level of pyrogens goes down, the hypothalamus resets back to a normal temperature level.
The mechanism of exactly why fever is utilised by the body is not completely understood. What a shock. The theories imply that its good because it allows white cells to reproduce faster, for phagocytosis to happen quicker, and to reduce the effect of endotoxins released by bacteria. The argument against is that if you have a temperature of 712°C, it doesn't really matter how fast you are phagocytosing, you are still screwed.
Clinical and Associated Features
High temperature is obviously the key one.
- Feeling hot to the touch.
- Complaining of being hot or cold.
- Being red and flushed.
Other symptoms that might be mentioned include:
- Feelings of cold
- Increased heart rate
- Increased muscle tone (stiffness)
- Infection is the biggie. By a long way
- Medicines such as antibiotics, narcotics, barbiturates, and antihistamines. These cause "drug fevers" due to adverse reactions, withdrawal, or by the drug's design.
- Trauma or injury such as a heart attack, stroke, embolisms, heatstroke, heat exhaustion, or burns.
- Haemolysis and haematological cancers.
- Other stuff - skin inflammation, arthritis, hyperthyroidism, some cancers, lupus, inflammatory bowel disease, metabolic disorder and gout.
You are hunting for infection, so:
- Blood tests:
- Sputum, urine and stool tests.
- Cultures, to give a positive confirmation, and helpful guide to correct antibiotics.
- Xray can diagnose chest infection, sinusitis, tuberculosis, bone infection.
Usually you don't actually treat a fever. You may treat the underlying infection or cause, but the raised temperature itself is usually not targeted.
The main thing to do is to make sure the patient is hydrated, and if they are drinking lots, make sure they take sports drinks to keep the blood salts topped up.