Background: Hematuria can be either grossly visible (macrohematuria) or only detectable under a microscope (microhematuria). Microhematuria is often asymptomatic and has a prevalence of 4-5% in routine clinical practice. It may be due to an underlying disease of the kidneys or the urogenital tract. In this article, we provide an overview of the causes of hematuria and of the recommendations of current guidelines for its diagnostic evaluation. A risk-adapted diagnostic strategy for the evaluation of asymptomatic microhematuria (aMH) is presented.
Methods: This review is based on pertinent publications retrieved by a selective search in PubMed, as well as on guidelines from Germany and abroad.
Results: Hematuria has many causes, and a broad urological and nephrological differential diagnosis must be considered. In the absence of high-quality scientific evidence, the recommendations of current guidelines for the diagnostic evaluation of hematuria are not uniform; this is particularly so for aMH. Microhematuria is said to be present when urine microscopy reveals three or more erythrocytes per highpower field. The basic diagnostic evaluation consists of a thorough history and physical examination, measurement of inflammatory parameters and renal function tests, and ultrasonography of the kidneys and bladder. Patients with non-glomerular aMH who have risk factors such as smoking, advanced age, and male sex are more likely to have relevant underlying conditions and should therefore undergo augmented, risk-adapted diagnostic evaluation with urethrocystoscopy, urine cytology, and, when indicated, CT urography. Patients with isolated glomerular hematuria are at elevated risk for renal disease and should undergo follow-up checks at six-month intervals.
Conclusion: Although hematuria is common, there is no uniform, internationally accepted, evidence-based algorithm for its diagnostic evaluation. All potential causes of hematuria must be considered, and all individual risk factors taken into account, so that an underlying disease requiring treatment can be identified or ruled out.