From the Guidelines
A clinically significant erythrocyte count in urine microscopy and culture (MCS) is defined as more than 3 red blood cells per high-power field (>3 RBCs/HPF) according to the most recent guidelines. This definition is based on the American Urological Association (AUA) and Society of Urodynamics, Female Pelvic Medicine & Urogenital Reconstruction (SUFU) guideline published in 2020 1. The guideline emphasizes that clinicians should define microhematuria as >3 RBCs/HPF on microscopic evaluation of a single, properly collected urine specimen.
The clinical significance of erythrocyte count in urine MCS depends on various factors, including the patient's symptoms, medical history, and other laboratory findings. Isolated hematuria without symptoms may require monitoring, while hematuria with symptoms like pain, fever, or decreased urine output needs prompt evaluation. The context matters significantly, as temporary and benign causes such as menstruation in women, strenuous exercise, or certain medications can cause hematuria.
Key points to consider in evaluating the clinical significance of erythrocyte count in urine MCS include:
- The presence of red blood cells in urine can indicate various conditions, including urinary tract infections, kidney stones, glomerular disease, trauma, or malignancy.
- Quantification of RBCs is important, as higher counts generally suggest more significant pathology requiring urgent assessment.
- The AUA/SUFU guideline recommends a risk classification system for patients with microhematuria, stratified as low-, intermediate-, or high-risk for genitourinary malignancy, based on factors such as age, sex, smoking, and degree and persistence of microhematuria 1.
In clinical practice, defining microhematuria as >3 RBCs/HPF provides a clear threshold for further evaluation and management, taking into account the patient's individual risk factors and clinical presentation.
From the Research
Clinically Significant Erythrocyte Count
- A clinically significant erythrocyte count on urine microscopy is generally considered to be three to five red blood cells per high-power field 2.
- The presence of erythrocytes in urine can be an indicator of various conditions, including urinary tract infections, kidney disease, and urinary tract neoplasms.
- The diagnostic value of urine tests, including erythrocyte count, can vary depending on the method used, with urine sediment microscopy being more sensitive than automated urinalysis for detecting red and white blood cells 3.
Diagnostic Considerations
- The presence of proteinuria, red cell casts, and elevated serum creatinine levels in addition to hematuria may indicate a more serious underlying condition and warrants prompt referral to a nephrology subspecialist 2.
- Patients with asymptomatic microscopic hematuria or persistent hematuria after treatment of a urinary tract infection require further evaluation, including cytology and imaging studies such as intravenous urography, computed tomography, or ultrasonography 2.
- Abnormal urine cytology results should be followed up with cystoscopy to complete the investigation 2.