Nephrology & urology · KIMS Secunderabad
Pyelonephritis (Kidney Infection) — Symptoms, When It Is Serious, and How It Is Treated
Pyelonephritis is a bacterial infection of the kidney — specifically of the renal parenchyma (the functional tissue of the kidney), the collecting system, and the renal pelvis. It is distinct from a lower urinary tract infection (cystitis — infection of the bladder) both in its severity and its potential consequences. Untreated or inadequately treated pyelonephritis can progress to bacteraemia (bacteria in the bloodstream), septic shock, renal abscess, or permanent kidney scarring — particularly in patients who are diabetic, immunocompromised, pregnant, or have an underlying urological abnormality such as kidney stones, obstruction, or vesicoureteral reflux.
Most cases of uncomplicated pyelonephritis in otherwise healthy adults respond well to a course of antibiotics and do not require hospitalisation. But a significant proportion — those with high fever, rigors, severe loin pain, vomiting, inability to tolerate oral medication, rapidly rising creatinine, diabetes, or suspicion of an obstructed infected kidney — require hospital admission, intravenous antibiotics, and urgent urological assessment. Distinguishing uncomplicated from complicated pyelonephritis is the critical clinical decision.
How pyelonephritis develops
The most common route of infection is ascending — bacteria from the perineum colonise the urethra, ascend to the bladder (cystitis), and then ascend further via the ureter to reach the kidney. This ascending pathway explains why pyelonephritis is far more common in women (shorter urethra, closer proximity of the urethra to the perineum) than in men. The most common causative organism is Escherichia coli (80 to 85% of community-acquired pyelonephritis), followed by Klebsiella, Proteus, Enterococcus, and Pseudomonas (more common in hospital-acquired and catheter-associated infections).
Haematogenous pyelonephritis — bacteria reaching the kidney via the bloodstream from a distant source of infection — is less common and is seen in intravenous drug users (Staphylococcus aureus), patients with endocarditis, or severely immunocompromised patients.
Symptoms — distinguishing upper from lower UTI
The clinical distinction between pyelonephritis (upper UTI) and cystitis (lower UTI) determines the urgency, the route of antibiotic therapy, and whether the patient needs hospital admission. The features below — particularly fever, loin pain, and systemic illness — point to pyelonephritis and require same-day assessment.
Features that point to pyelonephritis rather than cystitis
Each row contrasts the lower UTI (cystitis) picture with the upper UTI (pyelonephritis) picture — the right-hand feature is what should trigger urgent kidney infection assessment:
Fever — Lower UTI: absent or low-grade. Pyelonephritis: prominent — often above 38.5°C with rigors (shaking chills).
Loin/flank pain — Lower UTI: absent. Pyelonephritis: present — unilateral, ipsilateral to affected kidney, often radiating to groin.
Costovertebral angle tenderness — Lower UTI: absent. Pyelonephritis: present — pain on percussion of the back at the costovertebral angle.
Nausea and vomiting — Lower UTI: mild or absent. Pyelonephritis: often prominent — preventing oral antibiotics and fluid intake.
Dysuria and frequency — Lower UTI: present. Pyelonephritis: may be present (ascending infection started in the bladder).
Haematuria — Lower UTI: may be present. Pyelonephritis: may be present.
Systemic illness — Lower UTI: absent. Pyelonephritis: present — fatigue, malaise, anorexia.
Inflammatory markers — Lower UTI: absent or minimal. Pyelonephritis: significantly elevated — WBC above 15, CRP above 50, elevated procalcitonin.
Fever above 38.5°C with loin pain and vomiting — particularly in a diabetic, pregnant woman, or patient with known urological abnormality — is pyelonephritis until proven otherwise and requires same-day hospital assessment. Obstructed infected kidney (pyonephrosis) is a urological emergency. Call KIMS on 040-4488-5000.
Complicated vs uncomplicated pyelonephritis
The distinction between uncomplicated and complicated pyelonephritis determines whether outpatient oral antibiotics are appropriate or whether hospital admission is required. The two cards below summarise the KIMS approach.
Uncomplicated pyelonephritis
Occurs in a non-pregnant woman with normal urinary tract anatomy, normal kidney function, no urological obstruction, no diabetes, and no immunocompromise. Moderate symptoms — fever below 38.5°C, able to tolerate oral fluids, not systemically unwell. These patients can be managed with oral antibiotics (ciprofloxacin 500mg twice daily for 7 days, or co-trimoxazole for 14 days, based on local antibiotic susceptibility patterns) in the outpatient setting, with urine culture result review at 48 to 72 hours.
Complicated pyelonephritis — requires hospital admission
Any of the following: male patient (pyelonephritis in men almost always has an underlying urological cause), pregnancy, diabetes, immunocompromise (transplant recipient, HIV, chemotherapy), known urological abnormality (stones, obstruction, vesicoureteral reflux, neurogenic bladder), high fever with rigors, inability to tolerate oral medication due to vomiting, rapidly rising creatinine, sepsis criteria (hypotension, tachycardia, altered mental state), or clinical suspicion of obstructed infected kidney (pyonephrosis — see separate KIMS page).
Investigations at KIMS
Urine dipstick and microscopy
Leucocytes, nitrites, and bacteria on dipstick; white cell casts and bacteria on microscopy. White cell casts are specific for upper tract infection (they form in the kidney's tubular system, not in the bladder).
Midstream urine culture and sensitivity
The essential test. Identifies the causative organism and its antibiotic susceptibility profile. Results available in 24 to 48 hours. Culture guides targeted antibiotic therapy — particularly important given the rising rates of extended-spectrum beta-lactamase (ESBL) producing E. coli in India.
Blood tests
Full blood count (leucocytosis), CRP and procalcitonin (elevated — procalcitonin is particularly useful for distinguishing upper from lower UTI), serum creatinine and eGFR, blood cultures (for patients with fever above 38.5°C or sepsis criteria).
Kidney ultrasound
Performed urgently in all complicated pyelonephritis to exclude: hydronephrosis (suggesting obstruction), abscess formation, emphysematous pyelonephritis (gas in the kidney parenchyma — a life-threatening complication in diabetics), and pyonephrosis. Normal ultrasound does not exclude early uncomplicated pyelonephritis.
CT abdomen with contrast
Performed in patients who fail to improve after 48 to 72 hours of IV antibiotics, or where abscess or emphysematous pyelonephritis is suspected on clinical grounds despite a normal ultrasound.
Treatment at KIMS
Treatment is determined by whether the pyelonephritis is uncomplicated, complicated, or associated with obstruction. The cards below set out the KIMS approach in each scenario.
Uncomplicated — oral antibiotics for 7 to 14 days
Ciprofloxacin (7 days) is first-line where local resistance rates permit. Co-trimoxazole (14 days) if susceptibility confirmed. Oral cephalosporins or amoxicillin-clavulanate where quinolone resistance is present. Urine culture result reviewed at 48 to 72 hours — antibiotics adjusted based on sensitivity if needed.
Complicated — IV antibiotics then step-down to oral
Admission and IV ceftriaxone or piperacillin-tazobactam initially — escalated to meropenem for ESBL organisms confirmed on culture. Step-down to oral antibiotics after 48 to 72 hours of IV treatment once the patient is afebrile and able to tolerate oral medication. Total duration 14 days. Blood cultures and repeat urine culture at 48 hours.
Obstruction — urgent drainage first, antibiotics second
An obstructed infected kidney (pyonephrosis) cannot be treated with antibiotics alone — the pus under pressure does not receive adequate antibiotic concentrations and the infection cannot resolve until the obstruction is relieved. Urgent drainage — ureteric stent placement or percutaneous nephrostomy — is the first priority, performed by the KIMS urology team. See the KIMS Pyonephrosis page for full detail.
Women with two or more episodes of pyelonephritis in 12 months, or a single episode of pyelonephritis with a structural urological abnormality, should be investigated for an underlying cause — kidney stone, vesicoureteral reflux, incomplete bladder emptying, or other structural factor — before being discharged with antibiotics only. At KIMS, a recurrent UTI and pyelonephritis workup includes renal ultrasound, urine cultures, and urological assessment.
Book a Kidney Infection Assessment at KIMS
Frequently Asked Questions — Pyelonephritis
The key distinguishing features are systemic symptoms and loin pain. A bladder infection (cystitis) causes dysuria (pain on urination), frequency, and urgency — but no fever, no back or flank pain, and no systemic illness. A kidney infection (pyelonephritis) causes all of this plus: fever above 38°C (often with rigors — uncontrollable shaking chills), pain in the back or flank on the affected side (loin pain), nausea and vomiting, and feeling systemically unwell with fatigue and loss of appetite. If you have a fever above 38°C and loin or flank pain alongside urinary symptoms, you almost certainly have a kidney infection that requires medical assessment the same day.
Uncomplicated pyelonephritis — in a non-pregnant woman with no diabetes or underlying urological problem, able to drink fluids and take oral tablets, with fever below 38.5°C — can be treated at home with oral antibiotics prescribed after a urine culture is sent. However, hospital admission is required if: you have a fever above 38.5°C with rigors, you are vomiting and cannot keep oral medication down, you are diabetic or immunocompromised, you are pregnant, or you feel significantly systemically unwell. Do not attempt to self-treat a suspected kidney infection with leftover antibiotics — the wrong antibiotic for the wrong organism may suppress symptoms temporarily while the infection worsens.
Untreated pyelonephritis can progress to: bacteraemia (bacteria entering the bloodstream from the infected kidney), urosepsis (septic shock from the urinary source — life-threatening), renal abscess (a localised collection of pus within the kidney requiring drainage), emphysematous pyelonephritis (gas-forming infection in diabetics — a nephrology emergency with high mortality requiring emergency nephrectomy in severe cases), and permanent kidney scarring that contributes to CKD. In pregnant women, untreated pyelonephritis can trigger preterm labour. These complications are preventable with prompt diagnosis and appropriate antibiotic treatment.
Pyelonephritis is uncommon in men — the male urethra is significantly longer than the female urethra, making ascending bacterial infection from the perineum much less likely. When a man develops pyelonephritis, there is almost always an underlying urological cause: urinary tract obstruction (from a kidney stone, BPH, or stricture), an anatomical abnormality, or a structural defect that allows bacteria to ascend more easily. For this reason, every man with pyelonephritis should have renal ultrasound, uroflowmetry, and a thorough urological assessment to identify and correct the underlying cause.
Acute pyelonephritis, promptly treated, usually resolves without permanent kidney damage in patients with normal urinary tract anatomy. However, recurrent pyelonephritis — particularly in children with vesicoureteral reflux, or in adults with recurrent obstructive episodes from stones — can cause focal kidney scarring (reflux nephropathy) that cumulatively reduces kidney function and may contribute to CKD and hypertension in adulthood. This is why investigating and treating the underlying cause of recurrent pyelonephritis is essential — treating each episode with antibiotics without addressing the structural cause allows scarring to accumulate.
Most patients with uncomplicated pyelonephritis feel significantly better within 48 to 72 hours of starting appropriate antibiotics. The fever typically resolves within 1 to 3 days. Fatigue and loin discomfort may persist for 1 to 2 weeks. A follow-up urine culture should be performed 5 to 7 days after completing antibiotics and again at 4 to 6 weeks to confirm the infection has been fully eradicated. Complicated pyelonephritis requiring IV antibiotics typically requires 3 to 5 days in hospital followed by oral completion of a 14-day total course. Full recovery of kidney function (if it was impaired during the acute illness) usually occurs within 4 to 8 weeks.
Yes — pyelonephritis in pregnancy is associated with significant risks for both mother and baby. Pregnancy increases the risk of upper tract infection because progesterone relaxes the ureteral smooth muscle, causing physiological hydronephrosis and ureteral dilatation that facilitates bacterial ascent. Untreated pyelonephritis in pregnancy can cause preterm labour, low birth weight, and maternal sepsis. All pregnant women with pyelonephritis are admitted to hospital for IV antibiotics, hydration, and foetal monitoring. Cephalosporins are the preferred antibiotics in pregnancy — quinolones are avoided. After treatment, a 7-day course of oral antibiotics and a suppressive low-dose antibiotic for the remainder of the pregnancy reduces recurrence.
KIMS Secunderabad — Dr. E. Ravi (Senior Consultant Nephrologist, critical care nephrology lead), 24/7 emergency nephrology, IV antibiotic protocols including ESBL coverage, ultrasound-guided assessment for abscess and obstruction, urology team for urgent stenting or nephrostomy in obstructed infected kidney, urine culture and sensitivity with NABL-accredited laboratory, recurrent UTI workup. NABH and NABL accredited. Emergency line: 040-4488-5000.