AKT · Renal & urology/Infection & obstruction

Pyelonephritis

Ascending (or haematogenous) bacterial infection of the renal pelvis/parenchyma — E. coli commonest

Overview

Infection of the upper urinary tract (renal pelvis and parenchyma), usually ascending from the bladder. It presents with the triad of fever/rigors, loin pain and lower urinary symptoms, and can progress to urosepsis. The critical exam move is recognising an OBSTRUCTED, infected system (a pyonephrosis) — which needs emergency drainage, not just antibiotics.

Recognise

Fever, rigors and loin/flank pain with renal angle tenderness, often with lower urinary symptoms (dysuria/frequency); nausea/vomiting
Systemic upset; may progress to sepsis/septic shock
Risk factors: female, pregnancy, stones/obstruction, diabetes, immunosuppression, catheter, structural abnormality

Red flags

OBSTRUCTED + infected kidney (pyonephrosis) — stone/obstruction with infection → EMERGENCY decompression (nephrostomy/stent) plus antibiotics
Sepsis/septic shock → Sepsis Six; emphysematous pyelonephritis (gas, often diabetic) → surgical emergency

Differentials & how to tell them apart

Lower UTIno fever/loin pain/systemic upset

Renal/ureteric stonecolicky loin-to-groin pain; but a stone can co-exist and obstruct an infected system

Other acute abdomen (appendicitis, biliary, gynae)different examination/imaging; always pregnancy-test

Investigations

Urine dipstick + MSU culture, blood cultures, FBC/CRP/U&Es/lactate; imaging — ultrasound/CT to exclude OBSTRUCTION or abscess (especially if not improving, diabetic, or a stone history); pregnancy test.

Management

Broad-spectrum antibiotics (7–10 days) + resuscitation; decompress an obstructed infected kidney

1Recognise fever + loin pain + urinary symptoms → send urine/blood cultures and start empirical antibiotics (IV if unwell), with fluids and Sepsis Six if septic.Gate: Image to exclude OBSTRUCTION: an obstructed, infected kidney (pyonephrosis) → EMERGENCY decompression (nephrostomy/stent) — antibiotics alone will not clear it.
2Target antibiotics to culture for 7–10 days; investigate underlying stones/structural abnormality; admit pregnant women for IV therapy. Consider abscess/emphysematous pyelonephritis if not improving.

Empirical broad-spectrum antibiotics (e.g. cefalexin, co-amoxiclav, ciprofloxacin, or trimethoprim per sensitivities) — 7–10 days — IV if systemically unwell/vomiting; then targeted to culture

IV fluids + Sepsis Six if septic — resuscitate; analgesia and antiemetics

Urgent decompression of an obstructed infected system — nephrostomy or ureteric stent — the key non-antibiotic intervention for pyonephrosis

Pregnancy: admit + IV antibiotics (e.g. cefuroxime) — lower threshold to admit; avoid contraindicated agents

Key points

Fever + rigors + loin pain + urinary symptoms = pyelonephritis → cultures + broad-spectrum antibiotics + resuscitate. THE trap: an obstructed infected kidney (stone + infection = pyonephrosis) needs EMERGENCY decompression (nephrostomy/stent), not just antibiotics. Image to exclude obstruction; admit pregnant women.

Monitor & prognosis

Clinical/sepsis response, cultures, renal function; imaging if not improving.

Good with prompt treatment; obstruction/sepsis/diabetes worsen outcome.

Source: NICE NG111 (pyelonephritis); cross-ref acute_care (sepsis)