✅ Model Answer:
• Diagnosis: Pyelonephritis (upper urinary tract infection) — fever (39.5°C), vomiting, flank pain, ill-appearing. Elevated WBC (18,000), CRP (12 mg/dL). UA shows leukocyte esterase +, nitrite +, WBC casts (indicating renal parenchymal involvement), and 2+ proteinuria. Urine culture would confirm E. coli >100,000 CFU/mL.
• Any other test: Urine culture with susceptibility, blood culture (if septic), renal/bladder ultrasound (to rule out hydronephrosis, abscess, or obstruction), serum creatinine, electrolytes. VCUG (if <2 years or recurrent/atypical UTI after acute infection resolves). DMSA scan (for renal scarring if indicated).
• What to do next: Admit for IV antibiotics — ceftriaxone (50 mg/kg/dose IV) or cefotaxime. IV fluids for hydration. Monitor urine output and clinical response. Switch to oral antibiotics after afebrile for 24-48h. Total duration 7-10 days.
• Follow-up plan: Renal/bladder ultrasound (already done). VCUG if <2 years or recurrent/atypical UTI. Monitor for complications: renal abscess, scarring. Follow-up for renal function and blood pressure.

✅ Model Answer:
• Pyelonephritis is an infection of the kidney (upper urinary tract), usually caused by bacteria ascending from the bladder to the kidneys.
• Common organisms:
- Escherichia coli: Most common (80-90%).
- Klebsiella pneumoniae
- Proteus mirabilis
- Enterococcus faecalis
- Staphylococcus saprophyticus (adolescents)
- Group B Streptococcus (neonates)
• Risk factors:
- Vesicoureteral reflux (VUR): Most important risk factor.
- Obstruction: Posterior urethral valves, stones, stricture.
- Voiding dysfunction: Infrequent voiding, dysfunctional elimination.
- Constipation
- Immunosuppression
- Age: More common in infants and young children.
- Female gender: More common after toilet training.

✅ Model Answer:
• Clinical features:
- Fever: High fever (≥38.5°C) — most common symptom.
- Flank pain: Costovertebral angle tenderness (in older children).
- Vomiting: Often present (due to systemic illness).
- Ill-appearing: Toxic appearance, lethargy, irritability (especially in infants).
- Lower UTI symptoms: Dysuria, frequency, urgency (may be absent in infants).
- Abdominal pain: In younger children.
- Dehydration: Poor feeding, decreased urine output.
- Jaundice: In neonates (indirect hyperbilirubinemia).
- Infants (<2 months): May present with fever, irritability, poor feeding, or sepsis.

✅ Model Answer:
• Urinalysis findings:
- Leukocyte esterase: Positive (indicates WBCs in urine).
- Nitrites: Positive (indicates bacteria).
- WBCs (pyuria): >5-10 WBC/hpf (elevated).
- WBC casts: Present — indicates renal parenchymal involvement (pathognomonic for pyelonephritis).
- Proteinuria: 1+ to 2+ (mild to moderate).
- Hematuria: May be present (RBCs).
- Bacteria: Present on microscopic exam.
- pH: May be alkaline (if Proteus).
• Gold standard: Urine culture (>100,000 CFU/mL of a single organism).
• WBC casts: Key differentiating feature from cystitis.

✅ Model Answer:
• WBC casts: White blood cells that have been trapped in the renal tubules and excreted in the urine.
• Significance:
- Indicates renal parenchymal inflammation (pyelonephritis).
- Pathognomonic: WBC casts are strongly suggestive of pyelonephritis (not seen in cystitis).
- Differentiates pyelonephritis from cystitis (which lacks WBC casts).
• Other conditions with WBC casts:
- Acute interstitial nephritis
- Glomerulonephritis (may have RBC casts + WBC casts).
- Renal transplant rejection.
- Pyelonephritis is the most common cause in children.
• Clinical pearl: If WBC casts are present, the patient should be treated as pyelonephritis (upper UTI).

✅ Model Answer:
• IV antibiotics (initial):
- Ceftriaxone: 50-75 mg/kg/day IV once daily (first-line).
- Cefotaxime: 50 mg/kg/dose IV q6-8h (alternative).
- If MRSA risk: Add vancomycin.
- If Pseudomonas risk: Piperacillin-tazobactam.
• Duration: 7-10 days total (3-5 days IV, then oral step-down).
• Transition to oral: When afebrile for 24-48 hours and clinically improved.
• Oral step-down antibiotics:
- Cephalexin (50-100 mg/kg/day).
- TMP-SMX (if susceptible).
- Amoxicillin-clavulanate.
• Supportive care:
- IV fluids (if vomiting or dehydrated).
- Antipyretics.
- Monitor urine output.
• Indications for admission: Toxic appearance, <2 months old, vomiting/dehydrated, unable to take oral medications.

✅ Model Answer:
• Complications:
- Renal abscess: Collection of pus in the kidney (requires drainage).
- Renal scarring: Permanent kidney damage → hypertension, CKD.
- Vesicoureteral reflux (VUR): May be unmasked or worsened.
- Urosepsis: Bacteremia → septic shock.
- Acute kidney injury (AKI): Prerenal or intrinsic.
- Pyonephrosis: Obstructed, infected hydronephrosis (surgical emergency).
- Delayed diagnosis: May lead to chronic pyelonephritis, hypertension, and end-stage renal disease.
- Death: Rare, but possible (especially in neonates or immunocompromised).
- Recurrent UTIs: Increased risk if VUR or voiding dysfunction is present.

✅ Model Answer:
• Prognosis:
- Good: With prompt IV antibiotics and supportive care.
- Renal recovery: Most children recover without complications.
- Renal scarring: 10-20% may develop scarring (especially if treatment is delayed or if VUR is present).
- Recurrence: 20-30% may have recurrent pyelonephritis (especially if VUR or voiding dysfunction).
- Mortality: <1% in children.
- Long-term: Risk of hypertension and CKD if scarring develops.
• Long-term follow-up:
- Renal ultrasound: 1-2 weeks after diagnosis (to rule out hydronephrosis, abscess).
- VCUG: If <2 years, recurrent UTI, or abnormal ultrasound (after acute infection resolves).
- DMSA scan: If renal scarring is suspected (3-6 months later).
- Blood pressure monitoring: Annually (if scarring).
- Antibiotic prophylaxis: If VUR is present.
- Education: Hydration, voiding habits, constipation treatment.