How should an asymptomatic adult with incidentally identified renal microliths (<2 mm) be evaluated and managed?

Management of Incidentally Detected Renal Microliths (<2 mm) in Asymptomatic Adults

Asymptomatic adults with incidentally detected renal microliths <2 mm require no immediate intervention, but should undergo urinalysis with microscopy to exclude hematuria, followed by metabolic evaluation if hematuria is present or if there is a family history of nephrolithiasis.

Initial Diagnostic Approach

Urinalysis and Microscopy

• Perform urinalysis with microscopy to confirm the absence of microscopic hematuria (defined as ≥3 red blood cells per high-power field), as dipstick testing alone is insufficient and should not trigger further evaluation without microscopic confirmation 1.
• If urinary tract infection is present, treat appropriately and repeat urinalysis six weeks after treatment; if hematuria resolves with treatment, no additional evaluation is necessary 1.
• Measure serum creatinine to assess baseline renal function 1.

Risk Stratification for Underlying Pathology

The presence of microliths may represent early stone formation, but the key clinical question is whether there is associated hematuria or risk factors for malignancy:

• If microscopic hematuria is confirmed (≥3 RBC/HPF), proceed with full hematuria evaluation including cystoscopy for patients ≥35 years old and upper tract imaging with multiphasic CT urography 1.
• If no hematuria is present and the patient is truly asymptomatic, imaging beyond the incidental finding is not routinely indicated 1.

Metabolic Evaluation

When to Pursue Metabolic Testing

Consider metabolic evaluation in the following scenarios:

• Positive family history of urolithiasis (present in up to 85% of pediatric cases with microlithiasis, suggesting genetic predisposition) 2, 3.
• Recurrent abdominal pain, dysuria, or hematuria even if current presentation is asymptomatic, as symptoms may precede sonographic detection of larger stones 2.
• Young adults with bilateral microliths, as metabolic abnormalities are found in 87% of urolithiasis cases 3.

Specific Metabolic Parameters to Assess

If metabolic evaluation is pursued, obtain 24-hour urine collection for:

• Hypercalciuria (most common abnormality, present in 88.9% of pediatric cases and 33.8% of all urolithiasis cases) 4, 3.
• Hypocitraturia (33.1% of cases) 3.
• Hyperoxaluria (26.5% of cases) 3.
• Hyperuricosuria (25.4% of cases) 3.
• Cystinuria (5.7% of cases) 3.

Imaging Follow-Up Strategy

No Routine Surveillance for Truly Asymptomatic Microliths

Do not order routine follow-up imaging for asymptomatic microliths <2 mm without hematuria or metabolic abnormalities, as this represents overutilization of resources and unnecessary radiation exposure 1.

When Follow-Up Imaging Is Indicated

Repeat renal ultrasound at 6-12 month intervals if:

• Metabolic abnormalities are identified (particularly hypercalciuria), as progression to larger stones occurs in 10.6% of pediatric cases with microlithiasis 4.
• Symptoms develop (flank pain, dysuria, hematuria), as clinical presentation may precede sonographic evidence of stone growth 2.
• Strong family history of nephrolithiasis is present 2, 3.

Imaging Modality Selection

• Ultrasound is the preferred modality for surveillance due to lack of radiation exposure, though it has limited sensitivity for detecting small solid lesions <3 cm 1, 5.
• CT is superior for stone detection (sensitivity 94-98% vs 19% for ultrasound) but should be reserved for symptomatic patients or when ultrasound findings are indeterminate 1.

Management Algorithm

For Asymptomatic Patients Without Hematuria:

1. Obtain urinalysis with microscopy and serum creatinine 1.
2. If no hematuria and no symptoms: Reassure patient, provide hydration counseling (maintain urine output >2L/day), and discharge from active surveillance 1.
3. If family history positive or metabolic risk factors present: Consider 24-hour urine metabolic evaluation and treat identified abnormalities (e.g., thiazide diuretics for hypercalciuria, potassium citrate for hypocitraturia) 4, 3.

For Patients With Microscopic Hematuria:

1. Proceed with full hematuria evaluation per AUA guidelines: multiphasic CT urography and cystoscopy for patients ≥35 years old 1.
2. If imaging reveals only microliths with no other pathology: Follow persistent microhematuria with annual urinalysis and consider repeat anatomic evaluation within 3-5 years 1.

Common Pitfalls to Avoid

• Do not pursue aggressive imaging or intervention for isolated microliths <2 mm in truly asymptomatic patients without hematuria, as natural history studies show spontaneous resolution in 37.7% of pediatric cases 4.
• Do not assume microliths are clinically insignificant in patients with recurrent symptoms, as they may represent early stone formation requiring metabolic intervention 2, 3.
• Do not rely on dipstick hematuria alone; always confirm with microscopy before initiating extensive evaluation 1.
• Do not order contrast-enhanced CT as initial imaging when ultrasound has already identified simple microliths, as this adds unnecessary radiation and cost 5.

Patient Counseling

Advise patients to:

• Maintain adequate hydration (target urine output >2L/day) to prevent stone growth.
• Return for evaluation if symptoms develop (flank pain, hematuria, dysuria).
• Consider metabolic evaluation if strong family history of kidney stones exists 2, 3.