Krygen XL As a result, the question "when to worry" or "better," when to act "about fever, is usually considered like a high-grade fever. Low-level fever that lasts more than 4-7 days needs to be investigated by a doctor while persistent fever (whether low, medium, or high level) should be explored further.Other terms are used to describe a fever or type of fever Prolonged or persistent fever is fever that lasts longer than 10-14 days; This is usually a low grade fever.Acute fever is fever with a sudden onset of illness that produces fever symptoms, an increase in body temperature set point .Constant fever is also called continuous fever; usually low-grade fever and has not changed much (around 1 ° C for 24 hours).Chronic fever : Fever lasts more than 3 days; some doctors consider intermittent fever that recurs several months to years as "chronic" fever. http://www.nizuni.com/