Infection · Moderate
This case is fictional and exists for study. It describes no real patient.
35 years · female
A 35-year-old female presents to the urgent care clinic with a 2-day history of burning pain on urination, increased urinary frequency, and urgency. Over the past 24 hours, she developed severe right-sided flank pain, shivering, and a high temperature. She is eating and drinking normally and has no significant past medical history. Physical examination reveals marked right costovertebral angle tenderness. Her abdomen is soft and non-tender with normal bowel sounds. A urine dipstick performed in the clinic is positive for nitrites, leukocyte esterase, and protein.
Vital signs
- HR
- 102 bpm
- BP
- 118/76 mmHg
- RR
- 18/min
- Temp
- 38.6 °C
- SpO₂
- 98%
Examination findings
- Marked right costovertebral angle tenderness
- Abdomen soft, non-tender, no guarding or rebound tenderness
- Normal heart sounds, chest clear to auscultation
Investigations
| White Blood Cell Count | 14.2 10^9/L | reference: 4.0-11.0 |
| C-Reactive Protein | 68 mg/L | reference: 0-5 |
| Serum Creatinine | 78 µmol/L | reference: 45-84 |
Question 1 of 3
Which of the following is the most likely diagnosis?
The clinical constellation of dysuria, frequency, fever, rigors, elevated inflammatory markers, and costovertebral angle tenderness is classic for acute pyelonephritis (upper urinary tract infection). Acute uncomplicated cystitis presents with lower urinary tract symptoms (dysuria, urgency) without systemic fever or flank pain. Acute pelvic inflammatory disease typically presents with bilateral lower abdominal/pelvic pain, cervical motion tenderness, and vaginal discharge. Renal calculus causes acute, severe, colicky flank pain radiating to the groin; while it can cause microhematuria, it does not typically present with infective dipstick changes and fever unless complicated by secondary infection.
Teaching point: Acute pyelonephritis is distinguished from simple cystitis by systemic manifestations such as fever, rigors, and costovertebral angle tenderness.
Question 2 of 3
According to standard clinical management guidelines, which of the following is the most appropriate next investigation to direct ongoing antimicrobial treatment?
A midstream urine (MSU) sample for culture and susceptibility testing should be obtained prior to initiating empirical antibiotic therapy in all cases of suspected acute pyelonephritis. Renal ultrasound scan or CT imaging is not routinely required in uncomplicated pyelonephritis responding to initial treatment; imaging is reserved for patients who remain febrile or clinically unwell after 48-72 hours of treatment, or if urinary obstruction or abscess formation is suspected. Serum procalcitonin is an inflammatory biomarker but is not routinely recommended for guiding initial diagnosis or management in standard urinary tract infection pathways.
Teaching point: A midstream urine culture and sensitivity test should always be sent prior to starting antibiotics in acute pyelonephritis.
Question 3 of 3
The patient is clinically stable, able to tolerate oral fluids and medications, and has no drug allergies. Which of the following is the most appropriate empiric oral antibiotic regimen for outpatient management?
FILE 1 — plab1--urinary-tract-infection--6ee0e4749d.json questions[2].explanation, replace with: "NICE NG111 lists four oral antibiotics for acute pyelonephritis in non-pregnant adults aged 16 and over, but two of them are conditional. Cefalexin 500 mg two or three times a day for 7 to 10 days is the empirical first choice here; ciprofloxacin 500 mg twice a day for 7 days is an alternative, restricted by the MHRA advice to reserve systemic fluoroquinolones for when other recommended antibiotics are inappropriate. Co-amoxiclav 500/125 mg three times a day and trimethoprim 200 mg twice a day for 14 days appear in the same table only if culture results are available and confirm susceptibility, so neither is an appropriate blind empirical choice — co-amoxiclav in particular, because resistance among UK urinary E. coli isolates is too high to rely on in an upper tract infection. Nitrofurantoin is effective only in lower urinary tract infection: it concentrates in urine but does not reach therapeutic levels in the renal parenchyma. Amoxicillin has high rates of E. coli resistance and is unsuitable as empirical monotherapy. Intravenous gentamicin is reserved for patients who are severely unwell, vomiting, or otherwise unable to take oral treatment." key_learning_points[2], replace with: "Oral cefalexin is the empirical first choice for acute pyelonephritis under NICE NG111; co-amoxiclav and trimethoprim are options only once culture confirms susceptibility, and nitrofurantoin is unsuitable for upper tract infection." FILE 2 — plab1--urinary-tract-infection--5acb5d7a43.json questions[2].explanation, replace with: "NICE NG111 gives oral cefalexin 500 mg two or three times a day for 7 to 10 days as the empirical first choice for acute pyelonephritis in a non-pregnant adult who can tolerate oral treatment and does not require admission; ciprofloxacin 500 mg twice a day for 7 days is an alternative, reserved under MHRA fluoroquinolone advice for when other recommended antibiotics are inappropriate. Co-amoxiclav and trimethoprim appear in the same table but only if culture results are available and confirm susceptibility, so neither is given blind. Nitrofurantoin is ineffective in pyelonephritis because it does not achieve therapeutic concentrations in the renal parenchyma. A 3-day trimethoprim course is a lower urinary tract infection regimen; the pyelonephritis course is 14 days and only where susceptibility is already known. Amoxicillin has high resistance rates among common uropathogens such as E. coli and is not recommended as empirical monotherapy." key_learning_points[2], replace with: "Nitrofurantoin is inappropriate for acute pyelonephritis because it does not penetrate the renal parenchyma; oral cefalexin is the NICE empirical first choice, with co-amoxiclav and trimethoprim reserved for culture-confirmed susceptibility." Nitrofurantoin is effective only for lower urinary tract infections (cystitis) because it achieves therapeutic concentrations in urine but inadequate levels in renal parenchymal tissue. Amoxicillin has high rates of Escherichia coli resistance and is unsuitable as empiric monotherapy for pyelonephritis. Intravenous gentamicin is indicated for severe pyelonephritis requiring inpatient admission or patients unable to tolerate oral intake.
Teaching point: Nitrofurantoin should not be used to treat pyelonephritis because it does not achieve therapeutic tissue concentrations in the renal parenchyma.
Key learning points
- Systemic symptoms like fever, chills, and costovertebral angle tenderness differentiate pyelonephritis from lower urinary tract infections.
- Always obtain a urine specimen for culture and sensitivity before administering antibiotics in pyelonephritis.
- Cefalexin or co-amoxiclav are recommended oral empiric agents for acute uncomplicated pyelonephritis; nitrofurantoin is unsuitable for upper tract infections.
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