Lysed blood in a urine test refers to a specific result on a urinalysis that requires careful interpretation. This result indicates that the red blood cells (RBCs) that entered the urine have ruptured, a process called hemolysis. When the cell membranes break down, they release their internal contents, primarily the oxygen-carrying protein hemoglobin, into the urine sample. This finding of free hemoglobin prompts further investigation into its source, which may be a condition within the body or an issue with the sample itself.
Understanding Hemolysis and Hemoglobinuria
The presence of blood components in urine falls into two main categories: hematuria and hemoglobinuria. Hematuria means intact red blood cells are present, which typically suggests bleeding somewhere in the urinary tract, such as the kidneys, ureters, bladder, or urethra. In contrast, hemoglobinuria is the technical term for free hemoglobin in the urine, signifying that the red blood cells have already burst. This lysis can occur either inside the body or externally within the urine sample itself after collection.
The distinction between these two findings is important because it changes the clinical focus. Intact RBCs usually point to a localized issue in the urinary system, such as stones or infections. Free hemoglobin, however, often suggests a systemic problem involving the widespread destruction of red blood cells throughout the bloodstream, known as intravascular hemolysis. The kidneys filter the excess free hemoglobin from the blood and excrete it into the urine.
How Laboratory Tests Detect Lysed Blood
The initial detection of blood in a urine sample is typically done using a chemical dipstick test. This test strip contains a reagent that reacts with the peroxidase activity of hemoglobin and myoglobin, causing a color change. The dipstick is sensitive and will turn positive whether it encounters intact red blood cells or free hemoglobin. A positive dipstick test for blood only indicates the presence of a blood component, not necessarily intact cells.
To determine if the blood is lysed, the lab performs a microscopic examination of the urine sediment. If the dipstick is positive but the microscopic view shows few or no intact red blood cells, the finding is interpreted as hemoglobinuria, or “lysed blood.” The positive chemical reaction confirms the presence of hemoglobin, while the absence of intact cells confirms that lysis has occurred.
Medical Conditions Leading to Internal Lysis
When red blood cell lysis occurs inside the body, the underlying cause is often a condition that triggers intravascular hemolysis. These systemic issues include certain types of hemolytic anemias, where the immune system or a genetic defect causes widespread RBC destruction. Severe conditions like major burns or certain snake venoms can also lead to massive red blood cell rupture.
Rhabdomyolysis is another condition that can produce a positive dipstick result for blood, interpreted as lysed blood. Intense muscle breakdown releases myoglobin into the bloodstream, which the kidneys filter. Since myoglobin is chemically similar to hemoglobin, the dipstick reacts positively, yet no RBCs are seen microscopically. Kidney infections or severe urinary tract infections can also cause localized lysis when the urine environment becomes hostile to red blood cells.
Non-Disease Factors Affecting Sample Integrity
Not every finding of lysed blood indicates a disease process, as lysis can occur after the sample is collected, resulting in a laboratory artifact. One common cause is very dilute urine, which has a low specific gravity and low osmolality. When red blood cells enter this hypotonic environment, water rushes into the cells, causing them to swell and burst before the sample is tested. This ex vivo lysis creates free hemoglobin that triggers the positive dipstick reading with few visible intact cells.
Delayed processing is another frequent cause of artifactual lysis. Red blood cells are fragile and will naturally degrade over time, especially if the urine sample is left standing at room temperature. Similarly, highly alkaline urine, with a pH above 7, is a less stable environment for red blood cells and can accelerate their breakdown. Proper sample collection and prompt analysis are important steps to prevent these external factors from distorting the test result.
Determining the Underlying Cause and Next Steps
Once lysed blood is detected, the next steps focus on determining the source of the free hemoglobin. Doctors often order blood tests to check for signs of intravascular hemolysis, such as low haptoglobin levels or elevated bilirubin, which confirm widespread RBC destruction in the body. They may also perform blood tests to assess kidney function, as high levels of free hemoglobin can potentially damage the renal tubules.
To distinguish between myoglobinuria and true hemoglobinuria, specialized chemical tests can be performed on the urine sample. For example, a test using ammonium sulfate can differentiate the two proteins, guiding the diagnosis toward muscle injury or a blood disorder. Follow-up imaging tests, such as renal ultrasounds or CT scans, may be necessary if a kidney or urinary tract source is suspected. Ultimately, the definitive treatment involves addressing the underlying condition, whether it is an autoimmune disorder, an infection, or simply re-collecting a properly handled urine specimen.