From the Guidelines
Yes, a non-obstructing kidney stone can cause microscopic hematuria. Microscopic hematuria refers to blood in the urine that is only detectable under a microscope, and it is a common finding in patients with kidney stones, regardless of whether the stone is causing obstruction or not. Even small, non-obstructing stones can irritate the urinary tract lining as they move or remain stationary, causing tiny amounts of bleeding that result in microscopic hematuria. This occurs because stones have rough, crystalline surfaces that can scrape against the delicate epithelial lining of the urinary tract.
Key Points to Consider
- The presence of microscopic hematuria in a patient with known kidney stones is not necessarily cause for immediate concern, but it should be monitored 1.
- If a patient has microscopic hematuria and symptoms like flank pain, it would be appropriate to evaluate for kidney stones using imaging studies such as a CT scan or ultrasound.
- Patients with asymptomatic microscopic hematuria and known kidney stones should maintain adequate hydration (typically 2-3 liters of water daily) to help prevent stone growth and facilitate passage of small stones.
Evaluation and Management
The American College of Physicians recommends that clinicians consider urology referral for cystoscopy and imaging in adults with microscopically confirmed hematuria in the absence of some demonstrable benign cause 1.
Important Considerations
- Hematuria may be an incidental finding on tests pursued for other purposes, given the multiplex nature of dipstick tests.
- The magnitude of the risk for underlying cancer varies greatly, and the quality of evidence informing practice creates uncertainty 1.
- Any episode of gross hematuria in an adult warrants consideration of urgent urologic evaluation, given the relatively high pretest probability of cancer or other clinically significant underlying conditions.
From the Research
Non-Obstructing Stones and Microscopic Hematuria
- Non-obstructing stones can cause microscopic hematuria, as stated in the study 2, which mentions that urinary calculi are one of the benign causes of microscopic hematuria.
- The study 3 found that microhematuria was more common in patients with ureteral stones, but it does not exclude the possibility of urolithiasis in patients without microhematuria.
- The presence of microscopic hematuria is not always a reliable indicator of the degree of hydronephrosis, as shown in the study 4, which found that patients without microscopic hematuria had larger stone sizes and more severe hydronephrosis.
- Imaging studies, such as computed tomography scans, are essential in diagnosing and managing stone disease, including non-obstructing stones, as mentioned in the studies 5 and 6.
- The study 4 suggests that imaging studies may be necessary for the diagnosis and treatment of emergency cases where microscopic hematuria is not detected in urinalysis, as the stone size may be larger and the degree of hydronephrosis may be more severe.
Key Findings
- Microscopic hematuria can be caused by non-obstructing stones 2.
- The absence of microhematuria does not exclude the possibility of urolithiasis 3.
- Imaging studies are crucial in diagnosing and managing stone disease, including non-obstructing stones 5, 6.
- The presence or absence of microscopic hematuria is not always a reliable indicator of the degree of hydronephrosis 4.