Blood tests are common medical procedures that involve collecting a blood sample, typically from a vein in the arm, to measure various components. Laboratories analyze these samples to assess overall health, diagnose conditions, monitor diseases, and check the effectiveness of treatments. The quality of the collected blood sample is crucial for obtaining accurate and reliable results.
Understanding Hemolysis in Blood Tests
Hemolysis refers to the breakdown or rupture of red blood cells (erythrocytes) within a blood sample. Red blood cells contain hemoglobin, a protein responsible for carrying oxygen throughout the body. When these cells break open, their contents, particularly hemoglobin, spill into the surrounding liquid portion of the blood, known as plasma or serum. This release of hemoglobin changes the sample’s appearance, often giving it a reddish or pinkish tint that can be visually detected.
The integrity of red blood cells is important because they are specialized for oxygen transport. Their membranes are designed to maintain their internal contents separate from the plasma. When this protective barrier is compromised, it releases substances that can affect the reliability of laboratory measurements.
Common Reasons for Hemolysis
Hemolysis in a blood sample frequently arises from issues during the collection process or subsequent handling. Improper blood collection techniques are a primary cause of in vitro hemolysis. For instance, using a needle that is too small can cause red blood cells to rupture as they are forced through the narrow opening. Drawing blood too forcefully with a syringe or applying excessive suction can also damage fragile red blood cells.
Vigorous mixing of blood tubes after collection is another common factor. Blood samples with additives, like anticoagulants, require gentle inversion to ensure proper mixing without causing cell damage. Prolonged application of a tourniquet can also contribute to hemolysis by increasing pressure in the veins. Improper needle placement or multiple attempts to access a vein can also traumatize red blood cells, leading to their breakdown.
Beyond collection, improper handling and storage can induce hemolysis. Exposing blood samples to extreme temperatures, either too hot or too cold, can cause red blood cells to burst. Freezing blood samples, for example, can damage the red cell membrane. Delayed processing or prolonged storage of samples before analysis may also increase the risk of hemolysis.
How Hemolysis Affects Test Results
When red blood cells lyse, they release their intracellular contents into the plasma or serum, significantly interfering with laboratory test results. Substances like potassium, lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) are found in much higher concentrations inside red blood cells than in plasma. Therefore, when hemolysis occurs, the levels of these substances in the sample can become falsely elevated. For example, potassium levels can be up to 23 times higher in red blood cells than in plasma, leading to drastically skewed results.
Hemolysis can also cause false low readings for some analytes or interfere with various testing methods. This interference makes it difficult for laboratory instruments to accurately measure other blood components. Common tests affected include those for potassium, LDH, AST, and bilirubin. Because hemolyzed samples produce unreliable results, laboratories frequently reject them, necessitating a repeat blood draw for accurate diagnosis and treatment.
What Happens After Hemolysis Occurs
If a blood sample is hemolyzed, the most common outcome is the need for a re-draw. The compromised sample cannot provide accurate or reliable test results. Laboratories will typically notify the healthcare provider that the sample was unsuitable for analysis and a new one is required.
To minimize the risk of hemolysis during a subsequent blood draw, several steps can be taken. These include ensuring the phlebotomist uses appropriate venipuncture techniques, such as selecting the correct needle size and avoiding excessive force during collection. Communicating any previous issues with sample collection to the phlebotomist can also help them adjust their approach. A hemolyzed sample usually indicates a technical issue with the sample itself, rather than an underlying health problem.