Gross and Microscopic Hematuria

Excerpt

Hematuria is defined as the abnormal presence of blood in the urine. It is one of the most commonly diagnosed urological disorders, accounting for over 20% of all urological evaluations. While there are many classifications of hematuria (eg, intermittent or constant, glomerular or nonglomerular, symptomatic or asymptomatic), the most clinically useful is gross or microscopic (ie, microhematuria). Gross hematuria refers to visible blood in the urine. Microhematuria is the detection of urinary red blood cells (RBCs) on a dipstick or by microscopic urinalysis, though the visual appearance of the urine is normal.

The minimum criteria used by the 2020 American Urological Association Microhematuria Guideline to diagnose microhematuria is the unexplained finding in an uncentrifuged specimen on microscopic evaluation of ≥3 RBC/HPF. This guidance has been established due to the relatively high incidence of false positives and negatives when using dipsticks alone. Blood from recent urological procedures, urinary tract infections (UTIs), and contamination from rectal or vaginal bleeding must be excluded. In one study, only 41% of the patients diagnosed with microscopic hematuria by dipstick by primary care clinicians had microscopic analysis. Of those with microscopic analysis, only 24% had >3 RBC/HPF. This suggests that improved education regarding the definitions of hematuria would be useful to avoid unnecessary testing and referrals. Some sources recommend using the more stringent criteria of at least 2 or even 3 confirmed microscopic findings of hematuria. In such cases, where only a single finding of microscopic hematuria has been detected, periodic follow-up urinalyses for at least a year are suggested if no further workup is conducted after the initial diagnosis.

Microscopic hematuria can be further subdivided into symptomatic microhematuria, asymptomatic microhematuria with proteinuria, which is suggestive of glomerular disease, and asymptomatic microhematuria without proteinuria, which suggests possible urothelial malignancy. Microscopic urinalysis can also identify urinary infections and pertinent urinary sediment not detected by dipstick (eg, crystals and casts) that can help diagnose the underlying pathology. The absence of microscopic RBCs in dipstick-positive urine samples suggests myoglobinuria, hemoglobinuria from lysed erythrocytes, or some other cause of pseudohematuria. A microscopic examination of the urinary sediment must always confirm a presumptive diagnosis of microhematuria by dipstick. The most severe and devastating consequence of hematuria is malignancy. Many classifications exist to stratify patients into low-, intermediate-, and high-risk; a commonly used and validated system is the 2020 American Urological Association Guideline on Microhematuria Risk Stratification Guide. Evidence suggests that the majority of patients with true microhematuria are not appropriately referred to urology, which could lead to delayed diagnosis of malignancy.