Hemolysis refers to the rupturing of red blood cells in a blood sample, leading to the release of their internal contents into the surrounding fluid. This phenomenon primarily affects the integrity of a laboratory specimen. While hemolysis can occur naturally within the body, in the context of a lab sample, it typically indicates an issue with how the blood was collected or handled, rather than a health concern for the patient.
Understanding Hemolysis
Hemolysis involves the breakdown of red blood cells, also known as erythrocytes. When these cells rupture, they release their intracellular components, most notably hemoglobin, into the plasma or serum, which is the liquid portion of the blood. Hemoglobin, the protein responsible for the red color of blood, tinges the clear, yellowish plasma or serum, causing it to appear pink, red, or even dark red, depending on the extent of red blood cell destruction.
Their integrity is important for accurate laboratory testing because the concentrations of various substances inside red blood cells differ significantly from those in the plasma. The intact membrane of the red blood cell maintains this separation, and any compromise to this membrane leads to a mixing of cellular contents with the plasma, altering the sample’s composition.
Common Causes of Hemolysis
Hemolysis in a blood sample most frequently arises from events that occur before the sample reaches the laboratory, known as pre-analytical factors. One common cause relates to the venipuncture procedure itself, particularly a difficult or prolonged blood draw. Using a needle with too small a gauge can force red blood cells through a narrow opening, subjecting them to excessive shear stress that causes them to rupture. This mechanical trauma can also occur if the needle is partially occluded by the vein wall during collection.
Improper handling of the collected blood is another frequent contributor to hemolysis. Vigorously shaking the sample tube, rather than gently inverting it, can mechanically damage the fragile red blood cell membranes. Similarly, forcefully expelling blood from a syringe into a collection tube, or applying excessive pressure when drawing blood with a syringe, creates turbulence that can lyse cells. Additionally, issues with the sample tube itself, such as under-filling a tube containing anticoagulant, can create an imbalance where the higher concentration of anticoagulant damages the red blood cells. Extreme temperatures during sample transport or storage, such as freezing or excessive heat, can also lead to red blood cell lysis.
Why Hemolysis Matters for Lab Tests
The presence of hemolyzed red blood cells significantly impacts the accuracy and reliability of many laboratory test results. When red blood cells rupture, they release their intracellular contents, such as potassium, lactate dehydrogenase (LDH), and certain enzymes, into the surrounding plasma. This release can artificially elevate the measured levels of these substances in the sample, even if the actual levels in the patient’s bloodstream are normal. For instance, red blood cells contain approximately 23 times more potassium than plasma, so even minor hemolysis can lead to a falsely high potassium reading.
Hemoglobin released from broken red blood cells can also interfere with various laboratory assays by absorbing light at wavelengths used by automated analyzers, leading to inaccurate results. This spectral interference can affect tests for liver function, such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT), or other enzyme assays. The dilution effect from the released intracellular fluid can also alter the measured concentrations of other analytes, making the overall profile of the sample unrepresentative of the patient’s true physiological state. Consequently, a hemolyzed sample can lead to misinterpretation of results, potentially affecting clinical decisions.
Addressing a Hemolyzed Sample
When a laboratory receives a hemolyzed blood sample, it typically identifies the issue through visual inspection or automated systems. The reddish discoloration of the plasma or serum, caused by the released hemoglobin, serves as a clear indicator. Upon detection, the laboratory will often flag the sample as hemolyzed and may not be able to perform all requested tests accurately.
In most cases, a hemolyzed sample requires a re-draw. This means the patient will need to provide another blood sample for accurate test results. The re-collection ensures healthcare providers receive reliable data for accurate diagnosis and appropriate treatment plans.