Is 100.8 °F a fever in a child?

Notes

• One reading is not a diagnosis. Temperature moves with the hour of day — about 1 °F between the early-hours low and the late-afternoon high — as well as where on the body it is measured. A clinician reads it against your history and usually against a repeat, not on its own.
• Reference ranges differ between laboratories. The bands above follow the CDC and AAP definition of fever at 100.4 °F (38.0 °C). Your own report prints the range its analyser was calibrated against, and that printed range is the one to compare against — a difference of a few units between labs is normal and does not mean either is wrong.
• Where you measure changes the number. Rectal is the reference and reads highest; ear and forehead scanners are close to it; oral runs about 0.5 °F lower, and armpit about 1 °F lower again. The 100.4 °F threshold is defined on a rectal or equivalent reading, so 100.8 °F under the arm is not the same finding as 100.8 °F rectally. Whichever site you use, use the same one each time.
• Normal is a range, not 98.6 °F. That figure comes from a study published in 1868, and modern series put the adult average nearer 97.9 °F, drifting down slightly over the last century. Body temperature also swings through the day by about 1 °F — lowest in the early hours, highest in the late afternoon — so an evening reading of 100.8 °F and a morning reading of 100.8 °F do not carry the same weight.
• How the person looks matters more than how high the number is. In adults and older children, the height of a fever tracks poorly with how serious the cause is. Drinking, alertness, breathing effort and skin colour are what clinicians weigh. A fever that lasts more than three days, one that returns after settling, or one with a stiff neck, rash that does not fade under pressure, difficulty breathing, confusion or dehydration needs assessment regardless of the reading.