Urinalysis - Blood
Introduction
The urine of healthy individuals contains no blood, except for women during menstruation. In some diseases, however, blood occurs in the urine.
Hemoglobinuria and hematuria
The term 'presence of blood' in urine includes hemoglobinuria and hematuria.
Hemoglobinuria
Hemoglobinuria is the excretion of free hemoglobin, which appears in the urine in case of intravasal, intrarenal or urinary erythrocyte destruction. In intravasal hemolysis, hemoglobin passes to the urine when the plasma concentration of free hemoglobin exceeds 1.0 g/L. The urine is clear and red colored.
In acidic urine, hemoglobin is found in the form of methemoglobin and the urine is of brownish color, whereas in alkaline urine hemoglobin is found in the form of oxyhemoglobin and the urine is reddish. The so-called pseudoperoxidase activity of hemoglobin is mostly used for demonstration of hemoglobin in the urine.
Hematuria
Hematuria is the presence of intact erythrocytes in the urine. According to the amount of erythrocytes present in the urine, hematuria is divided into macro- (about 2500 erythrocytes per mL of urine or about 0.5 mL blood per 1 L urine) and microhematuria (cannot be seen by the naked eye and implies >5 erythrocytes per μL urine). Every finding of more than 5 erythrocytes per mL urine is considered pathologic. In women, the possible admixture of blood due to menstruation should always be ruled out.
Turbidity and red coloration can occasionally be observed by organoleptic examination of the urine containing erythrocytes. The urine clears with centrifugation, when erythrocytes remain in the precipitate and are simply demonstrated by microscopy.
The most common causes of renal and postrenal hematuria are urolithiasis, tumors of the kidneys and genitourinary tract, glomerulonephritis, and pyelonephritis.
The 'three-vessel test' is used to determine the genitourinary tract segment from which the hemorrhage causing hematuria originates. The patient is asked to urinate into three vessels (first, second and third urine flow). The presence of blood is determined in each urine specimen and the site of hemorrhage is localized on the basis of the results thus obtained.
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