Clues Pointing TO This Diagnosis

72-year-old woman with dysuria, urinary frequency, and suprapubic pressure beginning Monday — lower urinary tract (bladder) symptoms of an ascending UTI that can progress to the kidney
Progression over days to fever of 103°F with rigors (shaking chills) — systemic inflammation distinguishes pyelonephritis from simple cystitis
Right-sided flank/back pain — localization to the upper urinary tract is a cardinal feature of pyelonephritis
Costovertebral angle tenderness on exam — a classic physical finding supporting upper tract infection
Nausea accompanying the fever — systemic symptoms typical of pyelonephritis rather than isolated cystitis
Urinalysis with pyuria (white cells) and positive nitrites — indicates bacteriuria/pyuria supporting a UTI diagnosis
Urine culture growing E. coli — E. coli is the most common uropathogen and the confirmatory diagnostic test
CT showing perinephric fat stranding — imaging changes consistent with renal parenchymal infection
Age ≥65 and postmenopausal status — higher risk of pyelonephritis, bacteremia, and hospitalization
Symptoms that failed to resolve with hydration and did not stay confined to the bladder — the clinical course of an ascending infection reaching the kidney

Why It's NOT the Similar Diseases

NOT simple cystitis — cystitis causes dysuria, frequency, and suprapubic discomfort without fever, rigors, flank pain, or CVA tenderness, whereas Constance has systemic signs and upper-tract localization
NOT nephrolithiasis (renal colic) — stones cause colicky flank pain radiating to the groin, typically with hematuria and without fever/pyuria unless infection is present; her picture is dominated by fever, pyuria, and positive nitrites
NOT acute cholecystitis — that causes right upper quadrant pain with a positive Murphy sign and abnormal liver/biliary imaging, not CVA tenderness with pyuria and E. coli bacteriuria
NOT appendicitis — appendicitis causes migratory right lower quadrant pain and peritoneal signs, not flank pain with a positive urinalysis and CT renal fat stranding
NOT pelvic inflammatory disease — PID causes lower abdominal/adnexal pain and cervical motion tenderness in the context of an STI, not CVA tenderness with a nitrite-positive urine culture growing E. coli

Differential Diagnosis List

Acute cystitis — ruled out by fever, rigors, flank pain, CVA tenderness, and CT findings of renal involvement
Nephrolithiasis — ruled out by fever with pyuria/nitrites and CT showing fat stranding rather than an obstructing stone
Acute cholecystitis — ruled out by CVA tenderness with pyuria and a urine culture positive for E. coli rather than biliary findings
Appendicitis — ruled out by flank localization, positive urinalysis, and renal CT changes
Pelvic inflammatory disease — ruled out by absence of adnexal/cervical findings and presence of a nitrite-positive uropathogen

Key Distinguishing Test

Urine culture is the cardinal confirmatory test, typically yielding ≥10,000 CFU/mL of a uropathogen (usually E. coli); a supporting urinalysis shows pyuria and/or bacteriuria (nitrites, leukocyte esterase).
Cross-sectional imaging (contrast-enhanced CT) is not needed to diagnose typical pyelonephritis and is reserved for patients with sepsis/septic shock, known or suspected obstructing stone, urine pH ≥7.0, a new fall in GFR to ≤40 mL/min, or failure to improve after 24–48 hours.

Board Note

Classic profile: ascending UTI (cystitis → kidney) with fever, flank pain/CVA tenderness, nausea, and pyuria/bacteriuria; E. coli causes >90% of cases in healthy women and remains the leading pathogen in older women
Always obtain a urine culture with susceptibilities in suspected pyelonephritis and tailor therapy to the isolate; blood cultures rarely change management
Outpatient first-line oral therapy is a fluoroquinolone (e.g., ciprofloxacin or levofloxacin) or TMP-SMX when the isolate is susceptible; give an initial long-acting parenteral dose (e.g., ceftriaxone or an aminoglycoside) when local fluoroquinolone resistance may exceed ~10% or resistance risk is high
Nitrofurantoin and oral fosfomycin should NOT be used for pyelonephritis because they do not achieve adequate renal-tissue/blood concentrations
Duration: traditional courses are 5–7 days for a fluoroquinolone, ~7 days for TMP-SMX/most agents, and 10–14 days for oral beta-lactams; the 2025 IDSA complicated-UTI guideline supports shorter courses (5–7 days of a fluoroquinolone or 7 days of a non-fluoroquinolone) in patients improving clinically
Hospitalize/escalate for sepsis, inability to tolerate oral intake, hemodynamic instability, obstruction/abscess, or failure to improve; obstructing infected stones and renal abscesses require drainage/source control
Refer/prevent: in peri- and postmenopausal women with recurrent UTIs, vaginal (not oral) estrogen reduces recurrences and is recommended when there is no contraindication

“Constance’s Story”