Which symptom characterizes a urinary tract infection that has progressed to the upper tract?

A urinary tract infection (UTI) that has progressed to the upper tract, often referred to as pyelonephritis, is characterized by fever and systemic symptoms. This progression indicates that the infection has moved beyond the lower urinary tract (which typically involves the bladder and urethra) into the kidneys.

In this situation, systemic effects become more pronounced due to the body's immune response to a more severe infection. Fever is a common systemic symptom as the body attempts to fight the infection. Patients may also experience chills, malaise, and other systemic symptoms that signify a more serious condition.

In contrast to a lower tract infection, where symptoms might focus on local discomfort, increased frequency, and urgency of urination, the presence of fever points toward a more widespread physiological response and indicates that the infection could be affecting overall health more significantly. The development of systemic symptoms is an important marker that helps differentiate between the severity and progression of UTIs.