What is the most likely diagnosis in a 60‑year‑old woman with right‑sided flank pain, a urinary‑tract infection, markedly elevated erythrocyte sedimentation rate, leukocytosis, and chronic anemia?

Most Likely Diagnosis

The most likely diagnosis is acute complicated pyelonephritis with possible obstructive uropathy, given the constellation of right-sided flank pain, documented urinary tract infection, markedly elevated inflammatory markers (ESR and leukocytosis), and chronic anemia in a 60-year-old woman. 1

Clinical Reasoning

Why Pyelonephritis Is the Primary Diagnosis

• Right flank pain combined with a documented UTI is diagnostic of acute pyelonephritis, particularly when accompanied by systemic inflammatory markers. 1

• Markedly elevated ESR and leukocytosis indicate systemic infection (Grade 3 UTI), which distinguishes upper urinary tract infection from simple cystitis. 2 In the classification of UTI severity, Grade 3 comprises symptomatic infections with blood test changes indicating general infection, specifically elevated ESR and leukocytosis. 2

• Older women (>60 years) frequently present with atypical symptoms of UTI, including altered mental status, functional decline, or fatigue, making the diagnosis more challenging but no less likely. 3

Why Obstruction Must Be Ruled Out Urgently

• The combination of flank pain, UTI, and markedly elevated inflammatory markers raises concern for obstructive pyelonephritis or pyonephrosis, which can rapidly progress to urosepsis and is life-threatening without prompt drainage. 3

• Ureteral stones with secondary infection are significantly associated with urosepsis, occurring in 23% of bacteremic UTI cases versus only 3% of non-bacteremic cases (p = 0.03). 4

• Hydronephrosis is present in 36% of patients with urosepsis versus only 11% without bacteremia (p = 0.04), making imaging essential to exclude obstruction. 4

Immediate Diagnostic Algorithm

Step 1: Obtain Urine Culture Before Antibiotics

• Urine culture with antimicrobial susceptibility testing must be obtained before initiating antibiotics in all cases of pyelonephritis. 1

Step 2: Assess for Sepsis and Hemodynamic Stability

• Blood cultures (two sets from different sites) are recommended when the patient appears systemically ill or has high fever, which is likely given the markedly elevated inflammatory markers. 1

• Leukocytosis (WBC >12,000/μL) or leukopenia (WBC <4,000/μL) occurs in 68% of patients with urosepsis versus 29% without bacteremia, indicating this patient is at high risk. 4

Step 3: Urgent Imaging to Exclude Obstruction

Renal ultrasound should be performed immediately to evaluate for:

• Hydronephrosis or ureterectasis
• Renal or perinephric abscess
• Nephrolithiasis

3, 1

• Ultrasound detects hydronephrosis with 100% sensitivity and 90% specificity, making it the ideal first-line study to rule out obstruction. 3, 5

• If ultrasound shows hydronephrosis or is inconclusive, proceed immediately to contrast-enhanced CT abdomen/pelvis to characterize the obstruction and identify complications such as abscess or emphysematous pyelonephritis. 3, 1

Step 4: Initiate Empiric Antibiotics Immediately

Do not delay antibiotics while awaiting imaging or culture results. 1

For a 60-year-old woman who appears systemically ill:

• Ceftriaxone 1–2 g IV once daily is the preferred initial parenteral agent for hospitalized patients with pyelonephritis. 1

• Alternative: Cefotaxime 2 g IV three times daily or Cefepime 1–2 g IV twice daily. 1

• Treatment duration is 7–14 days total, with transition to oral culture-directed therapy once afebrile for 24–48 hours. 1

Why Chronic Anemia Is Relevant

• Chronic anemia in the setting of recurrent or persistent infection may indicate chronic pyelonephritis, renal insufficiency from repeated infections, or an underlying malignancy causing both anemia and urinary obstruction. 3

• If imaging reveals a pelvic mass causing ureteral obstruction, percutaneous nephrostomy (PCN) may be required for drainage, particularly in patients with advanced malignancy. 3

Critical Pitfalls to Avoid

• Do not assume this is uncomplicated pyelonephritis without imaging—the markedly elevated ESR and leukocytosis suggest complicated infection, and obstruction must be excluded within hours, not days. 3, 1

• Do not wait 72 hours to image if the patient appears septic or has markedly elevated inflammatory markers—these findings warrant immediate ultrasound to rule out obstruction. 3, 1

• Do not miss obstructive pyelonephritis—in patients with pyonephrosis, urinary tract decompression via PCN or retrograde ureteral stenting can be lifesaving, with patient survival of 92% when PCN is used versus 60% for medical therapy alone. 3

• Do not overlook diabetes or immunocompromise as risk factors—diabetes is significantly associated with urosepsis (32% vs. 3%, p = 0.004), and these patients require a lower threshold for imaging and admission. 4

Alternative Diagnoses to Consider

If imaging excludes obstruction and abscess:

• Renal infarction or hemorrhage from angiomyolipoma can present with acute flank pain and anemia, though UTI would be less likely. 6

• Pelvic malignancy with ureteral compression should be considered given the chronic anemia and age, particularly if imaging reveals hydronephrosis without stone. 3