Is a sore flank a sign of a kidney stone?

Is Sore Flank a Sign of Kidney Stone?

Yes, flank pain is a common presenting symptom of kidney stones (urolithiasis), though it is nonspecific and can be associated with other conditions requiring differentiation. 1

Clinical Presentation of Kidney Stone Pain

Kidney stone pain has characteristic features that help distinguish it from other causes of flank discomfort:

• The pain is typically colicky in nature, with waves of severe pain followed by periods of less intense discomfort 2
• Pain results from ureteral hyperperistalsis and obstruction with distension of the collecting system, not from external pressure 1, 2
• The pain does NOT worsen significantly with external flank pressure—if it does, consider alternative diagnoses like acute pyelonephritis or perinephric abscess instead 2
• Associated symptoms often include hematuria, dysuria, urinary frequency, and pain radiating to the groin 3, 4

Epidemiology and Risk Context

Understanding who is at risk helps frame clinical suspicion:

• Men are affected more commonly than women (10.6% vs 7.1% prevalence) 3
• By age 70, approximately 19% of men and 9% of women will have developed a kidney stone 1
• Recurrence rates are high—approximately 50% within 5 years after the first stone 1, 5
• Risk factors include obesity, metabolic syndrome, diabetes, hypertension, family history, and dehydration 3, 4

Diagnostic Approach

When flank pain raises suspicion for kidney stones, imaging is essential:

First-Line Imaging

• Non-contrast CT of the abdomen and pelvis is the gold standard, with sensitivity as high as 97% for detecting urolithiasis 1, 2
• Low-dose CT protocols (<3 mSv) maintain excellent diagnostic performance with pooled sensitivity of 97% and specificity of 95% 1
• CT allows accurate assessment of stone size and location, which are critical determinants of spontaneous passage rates and need for intervention 1

Alternative Imaging

• Ultrasound combined with radiography can serve as an alternative with sensitivity of 79-90% for clinically significant stones, particularly useful in pregnancy and to avoid radiation 2, 3
• However, gray-scale ultrasound alone shows reduced sensitivity (24-57%) compared to CT, especially for smaller stones and ureteral calculi 1
• Plain radiography (KUB) has limited sensitivity—only 72% for large stones (>5 mm) in the proximal ureter and 29% overall for stones of any size 1

Critical Pitfalls to Avoid

• Do not assume all flank pain is kidney stones—pain that worsens with external pressure suggests infection (pyelonephritis) or abscess rather than stone disease 2
• Do not order contrast-enhanced CT as first-line imaging—enhancing renal parenchyma during nephrographic phase may obscure stones in the collecting system 1
• Do not miss obstructing stones—look for secondary signs including hydronephrosis, perinephric inflammation, and ureteral dilation, as these indicate need for urgent intervention 1, 6
• Obstructing stones can progress to hydronephrosis and kidney failure if not managed appropriately 6

Stone Characteristics That Matter

• Stones >5 mm are less likely to pass spontaneously and may require intervention 1, 4
• More proximally located stones have lower rates of spontaneous passage 1
• Most stones are calcium oxalate (61%), followed by calcium phosphate (15%) and uric acid (12%) 3