Hemolyzed blood refers to a blood sample where red blood cells have ruptured. This rupture releases the cells’ internal contents into the surrounding fluid, impacting diagnostic accuracy. Understanding this phenomenon is important, as it can lead to unreliable test outcomes and affect patient care.
Understanding Hemolysis
Hemolysis occurs when red blood cell membranes break down, spilling their contents into the plasma or serum. The primary substance released is hemoglobin, the oxygen-carrying protein. When released into the clear plasma or serum, hemoglobin gives the sample a pink or reddish hue. The degree of discoloration indicates the extent of red blood cell destruction. This cellular disruption alters the sample, making it different from blood circulating in the body.
Common Causes of Hemolysis
Most hemolyzed blood samples occur outside the body (in vitro), rather than inside (in vivo). These external causes often arise during the blood collection process. Using an improper needle size, such as one that is too small, can damage red blood cells as they pass through, causing them to rupture. Similarly, excessive suction during blood draw or an improperly positioned needle can lead to mechanical stress on the cells.
Beyond the initial blood draw, sample handling also plays a role. Vigorous shaking or mixing of the blood tube can cause red blood cells to break apart. Also, prolonged tourniquet application before blood collection can induce hemolysis. Errors in sample processing, such as incorrect centrifugation speed or duration, or exposure to extreme temperatures during transport or storage, can contribute to red blood cell lysis.
Impact on Laboratory Results
Hemolysis affects the accuracy of many blood tests because released intracellular components contaminate the sample. Red blood cells contain higher concentrations of certain substances than plasma. For instance, potassium levels are approximately 20 times higher inside red blood cells than in plasma. When red blood cells rupture, they release this potassium, leading to a falsely elevated reading, known as pseudohyperkalemia. This can cause alarm for healthcare providers or mask a true potassium imbalance.
Another enzyme affected is lactate dehydrogenase (LDH), which is abundant in red blood cells. Hemolysis causes an artificial increase in LDH levels, making interpretation difficult for tissue damage or disease. Other analytes that can show falsely elevated levels due to hemolysis include magnesium, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and phosphorus. Conversely, some tests, like red blood cell counts and certain enzyme activities, can be falsely decreased or interfered with due to hemoglobin’s dilution effect or cellular debris. Hemolysis renders test results unreliable, often necessitating a repeat blood draw, which delays diagnosis and treatment.
Minimizing Hemolysis
Healthcare professionals employ strategies to minimize hemolysis during blood collection and handling. Proper venipuncture technique is important, including selecting an appropriate needle size (typically 20-22 gauge) to reduce shear stress on red blood cells. Ensuring the venipuncture site is dry after alcohol cleaning helps prevent cell damage. Gentle handling of the blood sample after collection is also important; tubes should be inverted gently to mix additives, not shaken vigorously.
Also, healthcare providers ensure blood collection tubes are filled to their correct volume, as an incorrect blood-to-anticoagulant ratio can promote cell rupture. Limiting tourniquet application to less than one minute reduces the risk of hemolysis. While medical staff control most preventive measures, patients can contribute by staying hydrated and relaxing during the blood draw, which can make veins more accessible and reduce the likelihood of a difficult collection. If hemolysis still occurs, effective communication between the laboratory and the clinician is important to determine if the sample needs to be recollected.