When Kidney Stones Do Not Bleed: Rethinking Hematuria

Source: Pournasiri Z, Mohammad Taheri M, Fatollahierad S, et al. Hematuria as a diagnostic marker in pediatric nephrolithiasis without acute obstruction or infection. Pediatr Nephrol. 2026;41(3):747-753. doi: 10.1007/s00467-025-07032-5.Investigators from Shahid Behreshti University of Medical Sciences, Tehran, Iran, conducted a retrospective study to estimate the frequency of hematuria in children with nephrolithiasis or nephrocalcinosis and evaluate the association between stone characteristics and hematuria. Patients 1 month to 18 years old diagnosed with nephrolithiasis or nephrocalcinosis in 2022 or 2023 at a single institution in Iran were included in the study. Children with acute urinary tract infection or confirmed obstruction were excluded. The diagnosis of nephrolithiasis or nephrocalcinosis was based on ultrasound findings, with radiographs or CT used if clinically indicated. Demographic, clinical and laboratory information were collected on study children; specific criteria were used to define hypercalciuria, hyperoxaluria, and hyperuricosuria. Hematuria was defined as the presence of ≥5 RBCs/HPF in a centrifuged urine specimen. The number, size, and location of stones was documented. The primary outcome was presence of hematuria in children with nephrolithiasis or nephrocalcinosis. Secondary outcomes included hematuria in patients with stones in different locations, stone size, and location. The association between stone characteristics and hematuria were assessed with chi-square, Kruskal-Wallis, and Mann-Whitney U tests.Data were analyzed on 260 patients with a mean age of 5.0 ±4.6 years. Metabolic abnormalities were detected in 146 (56.2%) study patients, including hypercalciuria in 36.9%, hyperoxaluria in 27.3%, and hyperuricosuria in 20.0%. Among all included study children, 40.0% had hematuria (≥5 RBCs/HPF). Hematuria was present in 91 of 216 (42.1%) patients with nephrolithiasis and 13 of 44 (29.5%) of those with nephrocalcinosis. Stones in the lower tract were frequently associated with hematuria, including 69.4% of children with stones in the ureter (P = 0.001) and 100% with bladder stones (P = 0.006). Rates of hematuria for patients with upper calyceal stones were 43.2%, 33.7% with middle calyceal, and 30.9% with lower calyceal stones. Stones located in the lower calyces were associated with a lower frequency of hematuria (P = 0.005). Patients with stones in the lower tract had significantly higher RBC counts per HPF than those with upper tract stones (P <0.001). Neither stone size nor number were statistically associated with rates of hematuria (P = 0.177 and P = 0.161, respectively).The authors conclude that hematuria is frequently absent in children with nephrolithiasis or nephrocalcinosis.Dr Rhone has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.When evaluating pediatric patients with suspected stones, hematuria sometimes is regarded as a gatekeeper finding.1 If there’s blood in the urine, the child needs imaging; if the urine is negative, the clinician needs to expand the differential.2 Yet, clinicians who care for children with kidney stones have long recognized a mismatch between this teaching and experience, as stones are frequently encountered in the absence of hematuria, especially when evaluating patients who present without acute renal colic.3,4 The current study provides an opportunity to recalibrate expectations—not by challenging the biology of stones, but by clarifying the clinical context in which hematuria does and does not appear.The study’s critical insight emerges when the population under study is carefully considered. Patients with acute obstruction, infection, or renal colic were excluded—leaving a cohort enriched with the types of pediatric patients more often encountered in clinical practice, in whom stones present subacutely, are detected during evaluation of nonspecific symptoms, or are even entirely asymptomatic. In this group, the absence of hematuria was the norm rather than the exception: Only 40% of patients with radiographically-confirmed stones had hematuria.This finding is not paradoxical, but expected. Non-obstructing calyceal stones, particularly those in the lower pole, often are relatively immobile, with minimal urothelial contact. Similarly, nephrocalcinosis represents a parenchymal rather than a mucosal process. In contrast, ureteral and bladder stones were strongly associated with hematuria. Taken together, these observations reinforce the pathophysiologic concept that hematuria is a marker of urothelial inflammation and best reflects where stones are.The key message of the current study, then, is not that hematuria lacks value, but rather, that bleeding is neither a dominant nor defining clinical signal across the spectrum of pediatric nephrolithiasis. The results of the study highlight the limitations of urinalysis when applied outside the acute setting and support a diagnostic approach that prioritizes clinical suspicion and imaging rather than reliance on a single laboratory finding. In so doing, it reframes hematuria not as a prerequisite for diagnosis, but as a potentially useful contextual (and anatomically localizing) clue.The absence of hematuria in pediatric nephrolithiasis is common, predictable, and largely explained by stone location and clinical context.