[The red urine]

The occurrence of red urine is a disconcerting sign for the patient. Hematuria is the most common cause for the red colour of the urine. However, certain drugs and food can also cause red urine. Visible blood in the urine is called macrohematuria; when blood is only detected by microscopic examination this is termed microhematuria. The cause of micro- or macrohematuria must be determined carefully. Both renal and extrarenal diseases can cause hematuria. Among the renal diseases certain glomerulonephritides (IgA nephropathy, Alport's syndrome) are frequent causes of asymptomatic microhematuria. Extrarenal causes include nephrolithiasis, tumours, or urinary tract infections. Microscopic analysis of the urinary sediment, ultrasound examination and other radiological tests are essential to establish a correct diagnosis. The diagnostic steps and differential diagnosis for a patient with red urine or microhematuria are described in detail in the present article.