01OverviewDefinition, clinical context and the essential points that orientate the chapter.
An obstructed infected kidney combines impaired urinary outflow with a source that can rapidly cause systemic illness. The presentation may include fever and colic, but neither dramatic pain nor complete anuria is required. A unilateral obstruction can exist while the other kidney continues producing urine, and older or immunosuppressed patients may have muted symptoms. The important inference is anatomical: infected urine cannot drain adequately, so antimicrobial treatment alone may be insufficient.
Decompression relieves the emergency; it does not necessarily remove the stone. Manipulating a stone during uncontrolled infection can worsen the clinical situation. Urology, anaesthesia, radiology and the acute team therefore coordinate a timely drainage procedure while treating sepsis and kidney injury. The chosen route must be feasible promptly and appropriate for the patient, with definitive correction planned once infection and physiology permit it.
Key points
- Infection with an obstructed collecting system requires urgent drainage as well as antibiotics; stone size does not remove that emergency.
- Contact urology immediately and coordinate imaging, cultures, antibiotics, resuscitation and a stent or nephrostomy decision.
- When pyonephrosis is suspected with acute kidney injury, obtain urinary tract ultrasound immediately, within six hours of assessment; necessary drainage should occur as soon as possible.
- Ureteric stenting and percutaneous nephrostomy both decompress the collecting system; choose using anatomy, physiology, access and expertise rather than an assumed universal superiority.
- Obtain urine from the drained system for culture, because a bladder sample may not represent infected urine trapped above the obstruction.
- Defer definitive stone treatment until the infection is controlled and sepsis has resolved, with a documented plan to avoid a forgotten stent or nephrostomy.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Obstructing calculus
A ureteric stone can impede flow from the kidney while bacteria infect the retained urine. Location and functional obstruction matter more to the emergency than stone diameter alone.
Other obstructing lesions
Stricture, tumour, external compression or altered postoperative anatomy can also obstruct an infected collecting system. The same need to assess urgent drainage applies beyond stone disease.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Pressure and stasis
Impaired outflow increases pressure within the collecting system and prevents normal clearance of infected urine. Ongoing pressure and inflammation can reduce the function of the affected kidney.
- 2Undrained infected material
A concentrated infected source can persist despite an active antibiotic. Decompression provides a route for infected urine to escape and creates an opportunity for direct upper tract culture.
- 3Systemic inflammatory injury
Infection can drive circulatory dysfunction and organ injury, while renal obstruction adds a separate physiological burden. Effective management must address both the systemic response and the blocked source.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Suspect the combination when fever or systemic illness accompanies renal colic, hydronephrosis, a known ureteric stone or another obstructing lesion. A relatively small stone can still obstruct a critical location.
A solitary functioning kidney, bilateral obstruction, acute kidney injury or anuria increases urgency. Continued urine output is not reassuring enough to exclude a unilateral infected obstruction.
Hypotension, tachypnoea, confusion, rising lactate or reduced perfusion signals escalating risk. Call senior and critical care help while the drainage pathway is being arranged, rather than completing a sequential series of referrals.
Pain may be less prominent after analgesia or in patients with altered sensation. A bladder culture can be negative after antibiotics or when infected urine is trapped upstream; combine results with imaging and clinical findings.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Urgent urinary tract imagingFirst step - Why
- Identify dilation and the likely site of impaired drainage.
- Interpretation and limitations
- In suspected pyonephrosis with acute kidney injury, NICE calls for immediate ultrasound within six hours of assessment. CT may define an obstructing stone or complicated anatomy more clearly; choose additional imaging with urology and radiology without postponing an urgent source intervention.
- 02
Blood and urine cultures - Why
- Identify organisms while urgent empirical treatment is organised.
- Interpretation and limitations
- Take blood cultures in systemic illness and obtain an appropriate urine specimen before antibiotics if this causes no meaningful delay. Send a new sample from the upper tract during decompression, as it can differ from bladder urine.
- 03
Renal function lactate and electrolytes - Why
- Measure organ effects and guide resuscitation and prescribing.
- Interpretation and limitations
- Compare creatinine with baseline and monitor potassium, acid-base state and urine output. Lactate and perfusion trends help assess systemic response, while rapidly changing renal function makes a single estimated filtration value an imperfect dosing guide.
- 04
Procedure readiness assessment - Why
- Identify factors that change the safest available drainage route.
- Interpretation and limitations
- Review haemodynamics, coagulation, antithrombotic medicines, prior reconstruction, pregnancy status and anaesthetic risk. Share relevant imaging directly with the procedural team; a route that cannot be delivered in time is not a satisfactory source-control plan.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Uninfected renal colic
A stone can cause severe colic without infection. Fever, rigors, inflammatory illness or organ dysfunction should prompt reassessment for the dangerous combination rather than being attributed to pain alone.
Unobstructed pyelonephritis
Kidney infection without impaired drainage may respond to antibiotics and supportive care. Imaging and clinical risk factors help identify when an apparently similar presentation has an additional source-control requirement.
Renal abscess
A focal renal or perinephric collection can maintain fever and pain without a ureteric blockage. Cross sectional imaging helps distinguish the anatomy and plan the appropriate source intervention.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Worked caseDrain the infected collecting systemFirst stepA fifty one year old woman has fever and an obstructing distal ureteric stone.+
- 1She has rigors, right flank pain, creatinine 156 from a baseline of 72 and lactate 2.7, with blood pressure 104/64. Imaging shows a six millimetre distal stone with hydronephrosis. Urology and the senior acute clinician are contacted immediately; cultures and resuscitation proceed together.
- 2Microbiology selects ceftriaxone 2 g intravenously daily using a recent susceptible isolate and the current renal risk, while urgent retrograde stenting is arranged because access is straightforward and the team is immediately available. This is drainage, not ureteroscopic stone fragmentation; pus obtained above the stone is sent for culture.
- 3The drained urine grows ceftriaxone- and cefalexin-susceptible Escherichia coli. Within twelve hours her lactate falls to 1.4, blood pressure improves and urine output is satisfactory. Creatinine falls to 96 over the next two days, supporting successful decompression and recovery rather than relying on the procedure note alone.
- 4DefinitiveOnce clinically well and taking oral medicines, she changes after three intravenous treatment days to cefalexin 500 mg orally three times daily for seven more days, completing ten days as agreed with the team. Definitive stone removal is booked after infection clearance, with a named clinician responsible for stent tracking and removal.
02Drainage choiceSelect a route that can work promptlyImaging confirms an infected obstruction requiring emergency decompression.+
- 1Ask whether retrograde ureteric access is likely to succeed and whether the patient can tolerate the planned anaesthetic approach. Prior reconstruction, impacted obstruction or difficult access may favour percutaneous drainage. A bladder catheter cannot bypass a stone obstructing a ureter, so lower-tract drainage does not replace the required upper-tract intervention.
- 2PreferredAssess the feasibility and risks of nephrostomy, including coagulation and the available safe access route. Ureteric stents and nephrostomies have comparable effectiveness for decompression; comparative evidence does not justify a blanket preferred route for every patient.
- 3Agree the procedure, timing, operator and contingency if the first route fails. In acute kidney injury due to upper tract obstruction, NICE advises drainage as soon as possible and within twelve hours of diagnosis when nephrostomy or stenting is used.
03After decompressionResolve infection and the underlying lesionDrainage has been performed but the patient still requires coordinated ongoing care.+
- 1Confirm that the stent or nephrostomy is functioning, review the drained culture and tailor antibiotics. Continued deterioration prompts reassessment for inadequate drainage, another collection, resistance or a different source.
- 2Monitor perfusion, renal recovery, electrolytes and post-obstruction urine losses. Excessive output needs an individual replacement and monitoring plan rather than automatic matching of every millilitre with intravenous fluid.
- 3DefinitiveDelay definitive stone treatment until infection is cleared and sepsis has resolved; arrange follow-up for the obstructing cause and temporary device. Explain symptoms that require urgent return, including recurrent fever, poor drainage or worsening pain. Improvement after drainage is not proof that the retained stone has passed; a normal creatinine or reduced pain alone does not establish that a temporary drain can be removed.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Ceftriaxone 2 g intravenous infusion
In the microbiology-selected example, administer 2 g intravenously every twenty four hours over at least thirty minutes; review culture and intravenous need within forty eight hours.This example is not universal empirical cover for ESBL organisms or every post-instrumentation infection. Exclude hypersensitivity to ceftriaxone or any other cephalosporin, as well as severe hypersensitivity to a different beta lactam; check renal plus hepatic status. Avoid concurrent calcium-containing intravenous infusions and flush shared lines for sequential adult use; never use lidocaine diluent intravenously. Reassess if neurological changes, severe diarrhoea or a serious rash occurs.
Cefalexin 500 mg capsules after stabilisation
For the susceptible oral continuation shown, prescribe 500 mg orally three times daily, counting previous active intravenous days within the agreed ten day total course.Do not use an oral switch to compensate for persisting obstruction or shock. Do not prescribe after cefalexin, formulation or cephalosporin hypersensitivity. A severe penicillin-reaction history requires specialist antibiotic choice. Check renal dose adjustment and the culture susceptibility; a result from an earlier episode is not a guarantee of current activity. Record the intended stop date and reassess diarrhoea or rash promptly.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Septic shock
An uncontrolled infected system can produce profound circulatory dysfunction. Escalating support and source intervention must be coordinated promptly when perfusion fails to improve with initial management.
Persistent renal impairment
Obstruction, infection and systemic hypoperfusion can damage kidney function. Renal recovery requires follow-up, particularly with a solitary kidney, bilateral disease or significant injury during the acute episode.
Device related problems
A temporary stent or nephrostomy can obstruct, displace or become a continuing infection risk. Tracking and a clear removal or exchange plan are necessary after the immediate crisis.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Before and after drainage, follow blood pressure, mental state, lactate when indicated and urine output. A completed intervention is not proof that the patient has physiologically recovered.
- Check creatinine and electrolytes serially, increasing frequency for marked abnormalities or rapidly changing urine output. Review medicines as renal clearance recovers or deteriorates.
- Inspect nephrostomy output or assess stent function if fever, pain or kidney injury persists. An absent or displaced drainage pathway warrants prompt procedural reassessment.
- At discharge, document antimicrobial duration, definitive lesion treatment, device removal responsibility and return precautions. The temporary drain must remain on an active tracking system until its endpoint is confirmed.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Size does not determine urgency
A stone that might otherwise pass spontaneously becomes a different problem when it obstructs an infected system. Medical expulsive strategies are not a substitute for emergency drainage in that setting.
Bladder urine can mislead
A closed or poorly draining upper system may contain organisms that are absent from a bladder sample. Culturing at decompression provides clinically relevant information for later narrowing.
No obligatory sequence of routes
There is no rule that every patient must fail stenting before nephrostomy, or the reverse. The team should choose the most suitable timely option and plan a practical rescue route.
Separate the two endpoints
Recovery from infection and definitive correction of the stone are related but distinct. Scheduling later stone treatment while tracking the temporary drain prevents an emergency success from becoming a follow-up failure.
11Common pitfallsFrequent interpretation and management errors.
- 01
Sending a febrile patient with an obstructing stone home because the stone is small overlooks the interaction between infection and impaired drainage.
- 02
Waiting for blood or urine susceptibility before starting antibiotics and organising drainage can allow rapid deterioration from an uncontrolled source.
- 03
Attempting definitive stone fragmentation during uncontrolled sepsis confuses treatment of the cause with the immediate need to decompress infected urine.
- 04
Assuming normal total urine output excludes obstruction ignores the continued contribution of the contralateral kidney in unilateral disease.