GPAtlas🧭 When to suspect
Acute pyelonephritis is infection of the renal pelvis and parenchyma – an upper urinary tract infection (UTI) – usually arising when bacteria ascend from the bladder, most commonly Escherichia coli. The classic presentation is loin or flank pain with fever, rigors and systemic upset, frequently (but not always) accompanied by lower urinary tract symptoms such as dysuria and frequency.
The clinical danger is twofold: under-calling it as “just cystitis”, and over-calling it from a positive dipstick alone. In older or frail patients the only clue may be new delirium, falls, or functional decline. The complications that matter are sepsis, acute kidney injury (AKI), renal abscess, an obstructed infected kidney, and – in pregnancy – preterm labour and fetal loss.
The core tasks in primary care are to recognise it, screen for sepsis, decide community versus hospital care, send a midstream urine (MSU) sample before starting antibiotics, and treat for longer than simple cystitis.
| Feature | Lower UTI (cystitis) | Upper UTI (pyelonephritis) |
|---|---|---|
| Symptoms | Suprapubic discomfort, dysuria, frequency, urgency | Loin/flank or back pain, renal angle tenderness, often with lower UTI symptoms |
| Systemic upset | Usually absent or mild | Fever, rigors, nausea/vomiting, malaise – systemically unwell |
| Risk | Often self-limiting; low risk | Risk of sepsis, AKI and abscess; can be life-threatening |
| Management | Short oral course; culture often not required | 7–10 day course; MSU mandatory; assess for admission |
Raise suspicion particularly in those who are pregnant, diabetic or immunocompromised, who have kidney stones or a structural urinary tract abnormality, who are catheterised, or who are male (a febrile UTI in a man is uncommon and warrants investigation for a structural or prostatic cause).
Source: NICE NG111 · NICE NG253
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