Medical Terminology for Kidney Infection Secondary to UTI
The medical term for a kidney infection secondary to a urinary tract infection is acute pyelonephritis. 1, 2
Definition and Pathophysiology
Acute pyelonephritis is the specific medical term used to describe infection of one or both kidneys that occurs when bacteria ascend from the lower urinary tract (bladder) through the ureters to reach the renal parenchyma and renal pelvis. 1, 2
- This represents an upper urinary tract infection, distinguishing it from cystitis, which is confined to the bladder (lower tract). 1
- The infection typically ascends from the urethra via the bladder into the upper urinary tract, with Escherichia coli causing 70-90% of cases. 3
- Less commonly, the kidney may be seeded by blood-borne infection (hematogenous spread). 3
Clinical Distinction from Lower UTI
Pyelonephritis is diagnosed based on specific clinical features that differentiate it from simple cystitis:
- Systemic symptoms including fever >38°C (100.4°F), malaise, nausea, and vomiting characterize upper tract involvement. 1, 2
- Flank pain or costovertebral angle tenderness is nearly universal in acute pyelonephritis and serves as the key distinguishing feature from lower tract infections. 1, 2
- Pyuria and/or bacteriuria must be present on urinalysis, along with fever, flank pain, or tenderness for diagnosis. 1
- Between 50-64% of children with febrile UTI show defects on renal cortical scintigraphy indicating acute pyelonephritis. 1
Important Clinical Caveat
Up to 20% of patients with pyelonephritis may lack typical bladder symptoms (dysuria, frequency, urgency), but flank pain remains the predominant feature. 4, 2 This is a common pitfall—the absence of lower urinary tract symptoms does not exclude pyelonephritis if fever and flank pain are present. 2
Long-term Sequelae
Pyelonephritis can cause renal scarring, which represents the most severe long-term complication and can lead to hypertension and chronic renal failure. 1 However, contrary to earlier beliefs, the long-term risk of chronic renal disease from pyelonephritis-related scarring is now recognized as low, with many previously attributed scars actually representing congenital renal dysplasia. 1