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Background: In our clinical practice we observed that -differently from patients with defined glomerulopathies- children with persistent isolated microscopic hematuria (PImH) usually shows at dipstick on first compared with second morning voiding lower degree of hematuria. We hypothesized that comparison of hematuria degree between first and second morning voiding (dipstick comparison test) could help in selection of patients needing of specific investigations. In this study, we aimed preliminarily validating our hypothesis., Methods: To define the risk of active glomerulopathies we used patients with defined glomerulopathies as cases. We prospectively enrolled 103 children during a one-year period. Sixty-nine of them had PImH, 16 microscopic/macroscopic hematuria (mMH), and 18 defined glomerulopathies. Inclusion criteria were: 1) persistent microscopic hematuria (≥1+ at dipstick) with or without defined glomerulopathy and/or previous episodes of macroscopic hematuria; 2) for the patients without defined glomerulopathy, having made regular biannual follow-up visits for at least 2 years in our department; 3) normal renal function and blood pressure at enrollment visit. We compared hematuria degree between first and second morning voiding. Possible findings were absence (NH), less degree (LH), similar degree (SH), and higher degree (HH) of hematuria in the first compared with second voiding., Results: At dipstick comparison test, 27.2% of patients presented NH, 44.7% LH, 28.1% SH, and none HH. NH showed specificity and PPV of 100% and significant area under receiver operating characteristic curve (AUROC = 0.66; 95%CI:0.55-0.78; p = 0.03) for absence of defined glomerulopathies. LH showed better sensitivity (76.9% Vs 33%) and NPV (78.9% Vs 24%) and lower specificity (88.2% Vs 100%) and PPV (87.0% Vs 100%) than NH for absence of defined glomerulopathies. Moreover, the LH showed a non-significant AUROC curve for presence of defined glomerulopathies. SH showed specificity of 80%, NPV of 91.9% and significant AUROC curve for presence of defined glomerulopathies (0.67; 95%CI:0.55-0.80; p = 0.009). The ROC curve analysis examining the delta of hematuria degree comparing first with second morning urine voiding showed a significant AUROC curve (AUROC = 0.78; 95%CI,0.68-0.89; p = 0.0002) with delta ≤ 1 showing the best sensitivity (80%) and specificity (66.7%) for defined glomerulopathies. None of the patients with defined glomerulopathies presented NH. Having SH presented relative risk for defined glomerulopathy of 5.1 (95%CI:1.9-13.6; p = 0.0007). Conversely, taken together NH and LH the RR was 0.2 (95%CI 0.1-0.5; p = 0.0007)., Interpretations: The dipstick on the first urine voiding underestimates the hematuria in about 70% of patients. The dipstick comparison test might easily screen patients with PImH and mMH needing of further investigations and treatment., (Copyright © 2020 Elsevier Ltd. All rights reserved.)