[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Kidney](https://durgical.com/en/general-pathology/areas/kidney/) › Acute pyelonephritis # Acute pyelonephritis - Lesion Bacteria climbing from the bladder infect the renal pelvis and interstitium, forming abscesses and pus in the tubules. Updated Nov 12, 2026 ## Key points - Organisms: E. coli first, then Proteus, Klebsiella, Enterobacter, Enterococcus; staphylococci suggest blood-borne spread. - Hallmark: white blood cell casts in the urine (pus formed in the tubules). - Predisposing: female sex, pregnancy, catheters, obstruction (stones, prostate), reflux, diabetes. - Complications: papillary necrosis, pyonephrosis, perinephric abscess, emphysematous pyelonephritis, sepsis. - Glomeruli resist infection and are usually spared. ## What it is Acute pyelonephritis is suppurative infection of the kidney's pelvis, tubules and interstitium. Almost always it ascends from the bladder, carried by gut gram-negative rods, most often Escherichia coli, helped by short female urethras, catheters, obstruction and vesicoureteral reflux. Less often, bacteria arrive in the blood (septicemia, endocarditis). Diabetes, obstruction and sickle cell disease favour the severe complications. ## Structure - Patchy, wedge-shaped yellow abscesses on the surface and cut face; one or both kidneys. - Neutrophils fill tubules and interstitium; tubules are destroyed and abscesses coalesce. - Papillary necrosis: grey-white to yellow necrotic papillary tips, sharply demarcated, with coagulative necrosis. - Pyonephrosis: pus trapped above an obstruction fills the pelvis and calyces. - Healing leaves scars that pull in the surface and flatten the calyx below them. ## Step by step - Gut bacteria colonize the periurethral area and distal urethra. - Adhesins (P fimbriae) help them stick to urothelium and climb into the bladder. - Catheters, urinary stasis and incomplete emptying let them multiply. - Vesicoureteral reflux pushes infected urine up the ureter to the pelvis. - Intrarenal reflux through open papillary ducts carries bacteria into the parenchyma, mostly at the poles. - Neutrophils flood tubules and interstitium, forming abscesses and white cell casts. ## Clinical notes - Sudden fever, flank pain and costovertebral tenderness, with dysuria and frequency from the coexisting cystitis. - Papillary necrosis presents with hematuria, colic or pieces of papilla in the urine; common in diabetes, sickle cell disease and analgesic abuse. - Recurrent infections on top of reflux or obstruction lead to chronic pyelonephritis. ## In the lab - Urine with pyuria, bacteriuria and white cell casts; culture identifies the organism. ## Memory aid Up from the bladder, in through the papilla, out as white cell casts. ## Test yourself Think of the answer, then tap the question to see it. ## What urine finding places a urinary infection in the kidney? White blood cell casts, which form in the renal tubules. ## What is the most common route of infection in acute pyelonephritis? Ascending infection from the lower urinary tract, helped by vesicoureteral reflux. ## Which three conditions predispose to papillary necrosis in pyelonephritis? Diabetes mellitus, urinary obstruction and sickle cell disease (analgesic abuse also). [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/acute-pyelonephritis/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer](https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/) ## Connections ## Related 5 - [Chronic pyelonephritis and reflux nephropathy](https://durgical.com/en/general-pathology/chronic-pyelonephritis-and-reflux-nephropathy/) - [Cystitis and bladder metaplasias](https://durgical.com/en/general-pathology/cystitis-and-bladder-metaplasias/) - [Urinary tract obstruction and hydronephrosis](https://durgical.com/en/general-pathology/urinary-tract-obstruction-and-hydronephrosis/) - [Diabetic nephropathy](https://durgical.com/en/general-pathology/diabetic-nephropathy/) - [Outcomes of acute inflammation: resolution, abscess, scar or chronic inflammation](https://durgical.com/en/general-pathology/outcomes-of-acute-inflammation-resolution-abscess-scar-or-chronic-inflammation/) ## Related conditions 10 - [Acute pyelonephritis](https://durgical.com/en/conditions/acute-pyelonephritis/) - [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/) - [Vesicoureteral reflux](https://durgical.com/en/conditions/vesicoureteral-reflux/) - [Renal papillary necrosis](https://durgical.com/en/conditions/renal-papillary-necrosis/) - [Catheter-associated urinary tract infection](https://durgical.com/en/conditions/catheter-associated-urinary-tract-infection/) - [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/) - [Benign prostatic hyperplasia](https://durgical.com/en/conditions/benign-prostatic-hyperplasia/) - [Diabetic kidney disease](https://durgical.com/en/conditions/diabetic-kidney-disease/) - [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/) - [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/) ## Microorganisms 3 - [Escherichia coli](https://durgical.com/en/microbiology/escherichia-coli/) - [Proteus mirabilis](https://durgical.com/en/microbiology/proteus-mirabilis/) - [Enterococcus](https://durgical.com/en/microbiology/enterococcus/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Acute Pyelonephritis](https://www.ncbi.nlm.nih.gov/books/NBK519537/) (StatPearls (NCBI Bookshelf), 2024); [Renal papillary necrosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000488.htm) (MedlinePlus, US National Library of Medicine, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/acute-pyelonephritis/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/acute-pyelonephritis/