Pyelonephritis

What is pyelonephritis?

Acute pyelonephritis is infection within the renal pelvis, usually accompanied by infection within the renal parenchyma. The source of the infection is often ascending infection from the bladder but haematogenous spread can also occur. The usual organisms are the same as for lower urinary tract infection (UTI) - eg, Escherichia coli, Klebsiella spp., Proteus spp., Enterococcus spp. Unusual organisms are occasionally seen - eg, mycobacteria, yeasts, and fungi and opportunistic pathogens such as Corynebacterium urealyticum. Repeated attacks of acute pyelonephritis can lead to chronic pyelonephritis, which involves destruction and scarring of renal tissue due to repeated inflammation.

Acute pyelonephritis

Incidence

Acute pyelonephritis can occur at any age. Around 1% of boys and 3% of girls will have had acute pyelonephritis by the age of 7 years.¹ It is most common in young women who are sexually active. Men who have pyelonephritis are more likely to have an underlying cause such as diabetes, renal stones, or kidney disease than women. Other age groups at higher than average risk include elderly patients, pregnant women, and infants.

Risk factors

These include:

• Structural renal abnormalities, including vesicoureteric reflux (VUR).

• Calculi and urinary tract catheterisation.

• Stents or drainage procedures.

• Pregnancy.

• Diabetes.

• Primary biliary cirrhosis.

• Immunocompromise.

• Neuropathic bladder.

• Prostate enlargement.

Pyelonephritis symptoms²

Onset of pyelonephritis is usually rapid with symptoms appearing over a day or two.

Symptoms include the following:

• Unilateral or bilateral loin pain, suprapubic pain, or back pain.

• Fever - varies and can be high enough to produce rigors; elderly or immunocompromised patients are more likely to have pyelonephritis without a fever.

• Malaise, nausea, myalgia, vomiting, anorexia, and occasionally diarrhoea.

• There may or may not be accompanying lower urinary tract symptoms with frequency, dysuria, gross haematuria, or hesitancy.

On examination:

• The patient looks ill.

• There is commonly pain on firm palpation of one or both kidneys, and moderate suprapubic tenderness without guarding. The combination of loin pain, fever, and nausea should particularly raise suspicion of acute pyelonephritis.

Pyelonephritis symptoms in children, especially when young, can be much less specific and culture of urine should be a routine investigation in pyrexial and generally unwell infants.

Differential diagnosis

• Abdominal abscess.

• Abdominal aortic aneurysm.

• Appendicitis.

• Causes of acute abdomen.

• Causes of loin pain.

• Diverticulitis.

• Ectopic pregnancy.

• Endometritis.

• Interstitial cystitis.

• Nephrocalcinosis.

• Nephrolithiasis.

• Oophoritis.

• Papillary necrosis.

• Pelvic inflammatory disease.

• Prostatitis.

• Renal corticomedullary abscess.

• Renal vein thrombosis.

• Salpingitis.

• Sexually transmitted infections.

• Urethritis.

• VUR.

• Vesicovaginal and ureterovaginal fistula.

Investigations

• Urinalysis:

  • Dipstick may be positive for blood, protein, leukocyte esterase, and nitrite, but 30% of patients with pyelonephritis will have a negative urine culture and dipstick. The urine is often cloudy with an offensive smell.

  • Always send a midstream specimen of urine (MSU) for microscopy and culture, or a catheter specimen if the patient is catheterised, although there is often poor correlation between symptoms and bacteriuria.

  • See the article on urinary tract infection in children for more information about getting a urine sample from a child.

• Inflammatory markers

  • In primary care, blood tests are unlikely to be part of the decision making process, due to the time taken to get results back; the tests below are more likely to be done for patients who are admitted.

  • CRP, ESR, and plasma viscosity may be raised; normal results would not rule out the diagnosis.

  • FBC shows elevated white cell count with neutrophilia.

  • Blood cultures may be positive.

  • Ultrasound may be done for admitted patients with a history of renal stones, kidney disease. or who have a high urinary pH; CT is sometimes added for those who are still febrile after 72 hours of treatment, who are deteriorating, with MRI being used in pregnant women to avoid the radiation from a CT scan. Ultrasound is usually used for children. See the separate Urinary tract infection in children article for details.³⁴

Pyelonephritis treatment and management

• Support: rest, adequate fluid intake and analgesia are important.

• Hospital admission: many patients can be managed in the community, providing they are otherwise healthy. Guidelines generally recommend considering admission for pregnant women, due to the risk of complications.² Other indications for admission include:

  • Severe vomiting.

  • Comorbidity such as diabetes.

  • Signs of sepsis (eg, tachypnoea, tachycardia, hypotension).

  • Dehydration or inability to take fluids/medication.

  • Severe pain or debility.

  • Urinary tract obstruction.

  • Oliguria or anuria.

  • Suspected complications (see 'Complications', below).

  • Uncertain diagnosis.

  • Social issues making treatment at home potentially unsafe.

  • Inadequate access to follow-up.

  • Relapse of symptoms as soon as antibiotics have been stopped.

All babies aged under 3 months with suspected pyelonephritis should be referred to paediatrics. For older children, the decision on where to treat will depend on the severity of the illness and whether there are any conditions inhibiting the absorption of antibiotics (eg, diarrhoea or vomiting).

• Antibiotics:

  • Treatment should be started empirically whilst awaiting culture and sensitivity.

  • First-line options are as follows:

    • Men and women who are not pregnant - cefalexin, co-amoxiclav, trimethoprim, or ciprofloxacin (bearing in mind Medicines and Healthcare products Regulatory Agency (MHRA) restrictions on the use of quinolones).⁵

    • Pregnant women not requiring admission - cefalexin.

  • Bear in mind local guidance and resistance patterns.

  • Change the antibiotics if culture results indicate that the infection is resistant to the antibiotic given.

• For patients with a longstanding urinary catheter, check that it is draining correctly and is not blocked. The catheter should be changed as soon as possible, but waiting for a catheter change should not delay antibiotic treatment.

• Surgery is occasionally required to drain renal or perinephric abscesses, or to relieve obstructions causing the infection (eg, stones).

Complications²

Potential complications include:

• Sepsis.

• Perinephric abscess (more common if there is urinary tract abnormality).

• Renal abscess, including emphysematous pyelonephritis (rare, life-threatening form with tissue necrosis and accumulation of gas in the renal parenchyma, perinephric space, and collecting systems - particularly occurs in obese, elderly women who have diabetes and develop urinary tract obstruction).

• Acute papillary necrosis, which is more likely in the elderly and those with diabetes (suggested by associated symptoms of renal colic).

• Pregnancy - tends to produce a more complicated course with significant risk of premature labour.

• Impaired renal function or renal damage potentially leading to acute kidney injury or chronic kidney disease (CKD).

Risk factors for complications include:

• Severe illness.

• Age over 65.

• Renal tract structural abnormality, or foreign bodies within the renal tract (including calculi and stents).

• Diabetes mellitus.

• Pregnancy.

• Renal transplant (especially the first three months).

• Immunocompromise.

Prognosis

Premature labour can occur in pregnant women. In other cases, there is usually uncomplicated recovery, providing there are no significant comorbidities.

Prevention

Recurrent UTI is defined by the National Institute for Health and Care Excellence (NICE) as follows:⁶

• In adults - ≥2 UTIs in six months or ≥3 UTIs in 12 months.

• In children - ≥2 episodes of upper UTI (such as pyelonephritis) or 1 episode of upper UTI and 1 episode of lower UTI, or ≥3 episodes of lower UTI. A timeframe is not given.

Preventative treatment for recurrent UTI may include the following:

• Vaginal oestrogen for women in the perimenopause or menopause.

• Single-dose antibiotic prophylaxis for women where there is an identifiable trigger (e.g. sexual intercourse).

• Methenamine hippurate for women who are not pregnant and where there has been no improvement after vaginal oestrogen or single-dose antibiotic prophylaxis (if they are appropriate).

• Regular antibiotic prophylaxis for men, women and children if there has been no improvement after the use of any of the methods above, where appropriate.

Chronic pyelonephritis

Chronic pyelonephritis is a characteristic scarring on the kidney which occurs after recurrent or persistent infections.

Epidemiology

There are few data available. VUR, which is a common risk factor, is found in up to one third of children investigated for UTI.⁷ A meta-analysis revealed that the prevalence of reflux was 31.1% in children who were evaluated for a UTI and 17.2% in those with normal kidneys who had voiding cystourethrogram for other indications, such as the diagnosis of hydronephrosis.⁸ Children who have recurrent episodes of infection or VUR are most likely to develop renal scarring.

Risk factors

• Any structural renal tract anomalies, obstruction, or calculi.

• VUR.

• Intrarenal reflux in neonates.

• Diabetes.

• Any factors predisposing to recurrent urinary infection - eg, neurogenic bladder.

Chronic pyelonephritis

Chronic pyelonephritis is a term used to describe changes caused by chronic vesicoureteric reflux; it may be more common if acute pyelonephritis has not been fully investigated or treated and where reflux has not been identified. Management will be in secondary care - good control of blood pressure is important and acute-on-chronic infections may need longer courses of antibiotics than are usually given. Complications can include end stage renal disease requiring dialysis.