Can point-of-care ultrasound (POCUS) be used to rule out ureteric colic in a patient without initial imaging?

POCUS for Ruling Out Ureteric Colic

POCUS alone cannot reliably rule out ureteric colic, but moderate-to-severe hydronephrosis on POCUS is highly specific (94.4%) for the presence of a symptomatic renal stone and may be sufficient to confirm the diagnosis without CT in select patients. 1, 2

Diagnostic Performance of POCUS

Overall Accuracy

• POCUS for detecting any degree of hydronephrosis has modest sensitivity (70.2%) and specificity (75.4%) for nephrolithiasis 2
• The positive likelihood ratio is 2.85 and negative likelihood ratio is 0.39, meaning absence of hydronephrosis does NOT rule out ureteric colic 2
• Emergency physicians with varied experience achieve similar accuracy (sensitivity 77.1%, specificity 71.8%) when using a simplified binary approach 3

When POCUS Performs Best

• Moderate or greater hydronephrosis on POCUS is highly specific (94.4%) for symptomatic renal stone, making it a "rule-in" test rather than a "rule-out" test 1, 2
• The finding of moderate-to-severe hydronephrosis combined with clinical presentation may be sufficient to make treatment decisions without CT in patients at moderate-to-high risk for ureteric calculi 1
• Any degree of hydronephrosis increases the positive predictive value to 88% for ureteral stones on subsequent CT 1

Clinical Algorithm for Using POCUS

Step 1: Risk Stratification

• Assess clinical probability of ureteric colic based on presentation (flank pain, hematuria, prior stone history) 1
• In moderate-to-high risk patients, POCUS findings carry greater diagnostic weight 1

Step 2: POCUS Interpretation

• If moderate-to-severe hydronephrosis is present: This is highly specific for obstructing stone; consider proceeding with conservative management or urologic consultation without CT 1, 2
• If mild hydronephrosis is present: Increases likelihood of stone but less definitive; consider adding KUB radiography (increases sensitivity from 39% to 68% for large stones) 1
• If no hydronephrosis is present: Cannot rule out stone (NPV only 65%); CT is needed if diagnosis remains uncertain or alternative diagnosis is suspected 1

Step 3: Consider CT When

• POCUS shows no hydronephrosis but clinical suspicion remains high 1
• Alternative diagnoses need exclusion (15% of patients have non-urological causes requiring different management) 4
• Severe hydronephrosis is present (rare finding that should prompt consideration of alternative causes beyond simple stone) 1
• Signs of infection are present (fever, leukocytosis) requiring urgent intervention 5

Critical Pitfalls to Avoid

• Do not use absence of hydronephrosis on POCUS to rule out ureteric colic—the negative predictive value is insufficient (65-87%) 1, 2
• Do not assume all patients with hydronephrosis need CT—in moderate-to-high risk patients with moderate-to-severe hydronephrosis, the diagnosis is sufficiently established 1
• Do not delay CT when infection is suspected—POCUS cannot distinguish pyonephrosis from simple hydronephrosis, and infected obstruction requires emergent decompression 1
• Do not ignore severe hydronephrosis—this uncommon finding should prompt consideration of alternative etiologies beyond simple stone disease 1

Prognostic Value of POCUS Findings

• Presence of any hydronephrosis on POCUS predicts larger stones (>5 mm) and increased likelihood of passage failure 2, 6
• Hydronephrosis on POCUS is associated with 3-fold increased risk of complications (RR 3.13) 3
• Patients with moderate-to-severe hydronephrosis are at higher risk of requiring urologic intervention 1, 5

Radiation Reduction Strategy

• The largest randomized trial demonstrated that using POCUS as the initial investigation resulted in lower cumulative radiation exposure with no increase in adverse events compared to CT-first approach 2
• This supports POCUS as a reasonable first-line test in appropriate clinical contexts, reserving CT for when POCUS is nondiagnostic or alternative diagnoses require exclusion 1, 2