Pyelonephritis

Exam Cram

• Pyelonephritis definition: kidney infection

• Commonly gram -ve bugs including E.coli tracking up from bladder

• Ix: urine  dip and culture, blood cultures, FBC, UEs, CRP, LFTs, lipase, BCHG & lactate; renal uss vs CTKUB 

• Important differentials renal calculi and aortic aneurysm/ dissection

• Gentamicin (good gram -ve cover) usually first line with sepsis IVF

• Step down to PO antibiotics as per urine culture sensitives

• Admit for 1-7 days

Definitions

• Pyelonephritis: kidney inflammation

• Lower urinary tract infection: infected bladder and urethra

• Upper urinary trac infection: kidney and ureter

• Urinary tract infection: any infection involving the urine from kidney to urethra

• Urosepsis: sepsis secondary to an urine infection

• Complicated pyelonephritis: pyelonephritis in men,  structurally abnormal urinary tract, immunocompromised.

Pyelonephritis vs urosepsis

Not all pyelonephritis leads to urosepsis but commonly it would if given adequate time, this depends at which point in infection progression you define as sepsis. On the other hand not all urosepsis has pyelonephritis but it is presumed if the individual is infected from the urine and is systemically unwell with a likely bacteremia (bacteria in blood) then the kidneys may or may not be infected. This is a little academic and in practice they are managed very similarly. A small difference is you would be more likely to perform a CTKUB in pyelonephritis than in urosepsis.

Schema: presentation -> sign -> diagnosis -> classification. 

Is pyelonephritis a meaningful diagnosis?

Pyelonephritis means kidney inflammation of which infection is the predominant cause. The management is principally with antibiotics which are dictated through culture sensitivities, usually from the urine.  Arguably any infective diagnosis should include the organism, therefore E.coli pyelonephritis sensitive to trimethoprim is a more meaningful diagnosis. The point is to empahaise the utility of growing the organism in infective processess such as pyelo (as well as pneumonia, cellulitis etc). 

Outline

Background

Assessment

History

• Demographics: 15-29, female

• PC: abdo pain, back pain, fevers, lower urinary tract symptoms (LUTS)(dysuria, urgency, frequency)

• HPC: 1 week of worsening abdo pain, unilateral flank pain with suprapubic pain, LUTS, fevers, nausea, vomiting

Examination

• Abdominal tenderness particularly left or right flank.

Observations 

• Temperature: pyrexia

• Heart Rate: tachycardia

• Blood pressure: hypotension

• Saturations & RR: normally saturating > 96% without oxygen, no tachypnoea

Investigations

Pyelonephritis is by definition an upper urinary tract infection and should be managed as per urosepsis. Investigations include a full septic screen to look for a source of infection. Blood and urine cultures are the two most important investigations as they will likely reveal the pathogen responsible (along with a lactate and creatinine). Most of the other investigations are likely to be normal and not effect management. A urine dip is not validated in over 65 years. A double +ve for leukocytes and nitrates in a healthy individual strongly predicts a urine infection but a bland one does not rule it out.  A CXR is useful to rule out a lower lobe pneumonia. A covid test should be done on anyone with a fever going into hospital. 

A full set of bloods is useful to gauge the inflammatory response (WBC and CRP). Although the CRP has not been correlated with mortality it is commonly presumed to be a marker of infection severity (though some medics will strongly contest this statement). A lactate is key in any septic patient and will does reliably predict severity and mortality. This is easily missed. A lactate is a very useful general indicator of how unwell a patient is. If the lactate is raised it should be repeated after a fluid bolus, see management for further information on fluids. Commonly anyone with abdominal pain gets an amylase to rule out pancreatitis. Although it is possible to get amylase normal pancreatitis (diagnosis is made with 2 out of the 3 criteria- symptoms, CT scan, raised amylase) it can be ruled out with a normal amylase and unconvincing history.  B (beta)- hcg is a pregnancy test and the blood test is more accurate than the urine test. This should be done as routine on any female of child bearing age. 

Finally gentamicin is usually the drug of choice and will require an up to date height and weight. 

Differentials & Imaging

Imaging is a slightly controversial topic. Important differentials of pyelonephritis are renal calculi and aorta pathology (abdo aortic aneurysm but rarely aortic dissection). It can be difficult to differentiate pyelonephritis from an infected renal colic. Some clinicians will CT KUB (urinary tract) nearly all pyelonephritis ?renal calculi, some will scan far fewer and be happy to trial antibiotics. A CT KUB is required if you are concerned about stones and this should be done within 24hrs. In the presence of a concomitant AKI (acute kidney injury) there is also an argument for doing a renal tract USS ?obstruction as renal USS are good at detecting hydronephrosis. Some departments like all CTKUB's to have a renal USS first but this can be duplicating work particularly if the CTKUB will be required regardless. 

An important reason for doing a CTKUB is that is should normally show either pyelonephritis (peri-nephritic fat stranding), a renal calculi or a normal tract. A normal CT KUB is an alarm bell for aortic pathology. This is a known diagnosis that is commonly missed with fatal results. An AAA or aortic dissection can commonly present with ?renal colic. A low threshold for doing a CT angiogram in this instance; a normal lactate, d-dimer, troponin and CXR can all point against this but cannot rule it out. It is for this reason why a CTKUB can be reassuring for pyelonephritis however it does come with a radiation risk (despite being a  non contrast scan).

Management

Pyelo-6. 

Management comprises of:

• Therapeutic control: antibiotics and fluids, change catheter

• Symptom control: analgesia and antiemetics

• Admit to general medicine or general surgery for 1-7 days (rarely can be discharged without admittance on PO antibiotics)

1. Antibiotics

Urine infections are typically gram negative anaerobes, E.coli the most common culprit. IV Gentamicin is the most common antibiotic given for its excellent gram -ve cover. Empirical cover is treating without prior urine or blood cultures. If there are previous urine or blood cultures these antibiotic sensitives should be taken into account. Temocillin and meropenem can be used in gentamicin resistant microbes. 

Usually a 7 day course is required (IV + PO). The PO option can be guided by any culture and sensitives grown. Common options include trimethoprim or ciprofloxacin. Note ciprofloxacin causes tendinopathy, lowers seizure threshold and lengthens the QTc. 

Simple cases can be treated with PO ciprofloxacin (7d) or trimethoprim (14d). NICE (2022) recommends co-amoxiclav or cefalexin and in pregnancy cefalexin 500mg 7-10 can be given orally in those not requiring admission. 

2. Fluid Status

Pyelonephritis cases can develop AKI from pre-renal hypoperfusion from systemic vasodilation or from direct renal infection. These typically require fluid resuscitation followed by maintenance. 2L over a couple of hours is a good volume for fluid resuscitation, particularly in a young person. If they are still experiencing nausea or unable to intake PO fluids, maintenance fluids of 2L/d for younger patients and 1.5L/d for the elderly. A lactate and creatinine are good measures of fluid status (as well as clinical exam looking at tongue dryness and skin turgor). Lactate suggests organ hypoperfusion from hypovolemia and it should be repeated after a 1.5-2L of fast IVF. Caution with fast IVF in the elderly and heart, liver and kidney failure.  

3. Catheter and urostomy

If there is a long term catheter in situ or urostomy this will likely be infected and it would be worth replacing this with a new one. If no catheter is in situ, then it is required for fluid balance in septic shock or if the patient goes into retention. Many will not require one.

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4. Analgesia

A cardinal symptom of pyelonephritis is pain, flank pain and this can be severe. Furthermore the patient can be experience nausea and vomiting and therefore decline the PO route. My schema for analgesia follows: paracetamol, nsaids, opioids and everything else. 

Paracetamol should be given regular concomitantly with opioids; in adults 1000mg QDS in individuals with a weight over 50kg. The main caution for paracetamol is allergy and deranged LFTs. Nsaids cause nephrotoxicity (as well as GI bleeding) therefore I would not routinely use them for pyelonephritis. 

This is also because the pain can be well controlled with opioids. Codeine can be given for mild pain (remember 30mg = 3mg of morphine sulphate PO immediate release) and avoid in severe AKI. Morphine can be give PO, S/C or IV. It is short acting and the dose can be titrated precisely. For acute pain therefore it is very effective and practical. Remember IV is three times as strong as PO and S/C twice as strong. If the patient is nil by mouth starting at 2mg IV (equivalent of 6mg PO) and review in half an hour ?up the dose. In AKI oxycodone can be preferred (1). 

5. Antiemetics

If this individual is experiencing nausea they may be also vomiting and vomit up any tablets. IV access is requiring for antibiotics so it may be sensible to give IV antiemetics. Ondansetron 4mg is my first line, obviously look at the BNF for contraindications and do not take this as medical or clinical advice. Ondansetron can prolong the QTc and is constipating. 

Metoclopramide 10mg can also be given IV. Again see BNF for contraindications. Metoclopramide is a dopamine receptor antagonist, i.e. it reduces dopamine. This is bad news in Parkinson's and for causing extrapyramidal side effects as both  are associated with low levels of dopamine. It also contraindicated in epilepsy. Furthermore it is a prokinetic and contraindicated after GI surgery. 

I have seen cyclizine given 50mg IV and I would personally strongly advocate against this because it can make patients 'high'. The IM option is preferable. 

6. Admission vs discharge

The majority will require admission. Isolated flank tenderness with lower urinary tract symptoms (dysuria, frequency, urgency) and mild inflammatory response in CRP/WCC could be managed with PO antibiotics however the majority present unwell and there is a low threshold for admitting due to the high risk of becoming septic. 

Indications for admission include administration of IV antibiotics and / or IVF, monitoring for deterioration and symptom control. Some patients will require HDU and ICU BP support from septic shock.

Admission Cycle

Admission Plan

The pyelo-10:

Full septic screen ?source:

1. Blood cultures

2. Urine cultures 

3. Urine dip

4. CXR

5. Covid 

Swab of any d/c in down below/ skin/ wound, phlegm etc.

Full set of bloods:

6. FBC, UEs, LFTs, CRP

7. Lactate

8. Amylase

9. B-HCG

For the gentamicin:

10. Height and weight 

Investigations

> Bloods: FBC, UEs, CRP, LFTs, Lipase, BHCG

> UA

> Urine cultures, blood cultures

[Prefer blood > urine BHCG]

Imaging: renal USS vs CTKUB vs CTAP

Plan

IV Antibiotics: gram negative cover, i.e. IV Gentamicin 200-400mg 1-4 days

IVF

• if septic 2L fast then maintenance is usually reasonable

• fill up until BP no longer becomes fluid responsive 

• even if tolerating PO I usually like one 1L because 

Symptom relief: 

• PRN Paracetamol 1g QDS, ibuprofen 400mg TDS (if nil AKI), morphine 2.5-5mg 4hrly [pain can be significant]

• PRN Ondansetron 4mg TDS (SE constipation, long QTC) usually first line due safety, cyclizine/ metoclopramide

Urinary catheter- if septic/ aki

Disposition

Admission: the age old debate, I won't be able to settle. I've seen pyelo admitted to general surgery/ urology and  general medicine. The surgeons will state there is no surgical option therefore nil indication for admission and urology would disagree with the premise the urinary system is their system and they are best managing a urine infection. Urology is indicated if there is a surgical complicating factor, i.e. nephrostomies in situ, that requires urology advice. These patients in the UK often are referred with abdominal pain ?surgical cause or ?urinary stone therefore to surgical assessment units. Once the scan shows pyelo the surgeons are stuck. 

Simple pyelo diagnosed in ED, in my mind, is a medical issue and should come under the medics. 

As discussed in the GP section a well patient with UTI + flank pain can be discharged with PO trimethoprim 300mg/ ciprofloxacin 500

Inpatient Reviews

Ward Round Reviews

Anecdotally significant pyelo / urosepsis patients look unwell for 3-4 days and go home on day 5/6. 

IV Antibiotics- a full course continued, usually of gentamicin (4 days). Once the CRP begins to fall (hence is often a daily test) antibiotics are converted to PO. This is also in conjunction with any significant urinary or blood culture growths. 

IVF can likely be stopped if PO intake is 2 litres or moved to maintenance if PO intake is very poor.  In young females (pyelo's pt population) the BP can be resting low and as long as its above 90/60 with good brain (?confusion) and kidney perfusion (?AKI) a lower BP can be tolerated. Giving repeated boluses over a few days can cause overload and if this is reqiured may be better in HDU for inotropes to support their BP. 

Discharge Planning

Discharge planning

Usually ready for discharge once 

• Improving on PO antibiotics for 24hrs

• Tolerating PO fluids

• Pain well controlled

Plan for discharge

PO Antibiotics as per sensitivities

Symptomatic relief

Safety netting

These individuals tend to be young and have no social barriers to discharge. The main barrier to discharge is IV antibiotics and once the patient is converted to PO antibiotics (IVOSTed) they are usually monitored for 24hrs to ensure they do deteriorate and discharged the following day. PO antibiotics are commonly started once the CRP begins to fall however some clinicians feel strongly this should not be the case as CRP does not predict severity. They should complete 7 days of PO + IV antibiotics and require no follow up post discharge (unless they are male, they may require a renal USS).

Resources and References

Written in 2025

Written in 2022