Pyelonephritis is derived from the Greek "pyelo" (pelvis), "nephros" (kidney), and "-itis" (inflammation). It is severe infectious inflammatory disease within the kidney. it can be acute recurrent or chronic.

Mostly caused by gram negative bacteria. Escherichia coli causes approximately 60% to 80% of uncomplicated infections.Other gram-negative pathogens include Proteus mirabilis (responsible for about 15% of infections) as well as Klebsiella (approximately 20%), Enterobacter , and Pseudomonas species. Less commonly, gram-positive bacteria such as Enterococcus faecalis , Staphylococcus saprophyticus , and S aureus may be seen

Complicated pyelonephritis occurs in older patients, diabetic patient, immuno-compromised patients and patients with complex urological problems or renal calculi

foreign body in urinary tract (e.g renal calculi, catheter)

full blood count. Leukocytosis is present in acute infection