Hemolysis occurs when red blood cells break open, releasing their internal contents into the surrounding plasma or serum. This process changes the sample’s composition, potentially affecting the accuracy of laboratory tests.
Understanding Hemolysis
Hemolysis is a process where the cell membrane of red blood cells ruptures, causing hemoglobin and other intracellular components to leak into the extracellular fluid. A normal blood sample, after clotting and centrifugation, yields a clear, straw-colored serum or plasma. A hemolyzed sample, however, often appears pink, red, or even brownish due to the presence of free hemoglobin.
The release of these components significantly alters the chemical environment of the sample. These substances are normally concentrated inside red blood cells, and their presence in the surrounding fluid can lead to inaccurate test results. The visual change serves as an initial indicator of this cellular disruption.
Why Blood Samples Hemolyze
Blood samples can hemolyze for several reasons, often related to the collection and handling procedures. One common cause is improper venipuncture technique, such as using a needle that is too small, which can physically damage red blood cells as they pass through. Drawing blood too slowly or with excessive suction on the syringe plunger can also contribute to red blood cell rupture.
Incorrect sample handling after collection is another frequent culprit. Vigorous shaking or rough transport of the blood tubes can mechanically stress and break open red blood cells. Additionally, improper mixing with anticoagulants, or the freezing and thawing of samples, can cause cell lysis. Factors like prolonged tourniquet application before blood draw can also lead to some degree of hemolysis in the collected sample.
Impact on Laboratory Test Results
Hemolysis significantly interferes with the accuracy of numerous laboratory tests by introducing substances not normally found in high concentrations in plasma or serum. For instance, potassium levels often appear falsely elevated because red blood cells contain approximately 25 times more potassium than plasma. Enzymes like lactate dehydrogenase (LDH) and aspartate aminotransferase (AST), abundant inside red blood cells, also show falsely increased levels. Phosphate and magnesium can similarly be falsely elevated due to their release from lysed red blood cells.
Conversely, hemolysis can lead to falsely decreased results for some tests. Bilirubin levels may appear lower because hemoglobin interferes with the chemical reactions used to measure it. Creatinine, amylase, and lipase measurements can also be negatively impacted, sometimes appearing falsely decreased or unreliable due to assay interference or dilution effects.
Beyond direct chemical interference, free hemoglobin released during hemolysis can absorb light at specific wavelengths used by laboratory instruments. This spectral interference can obscure true readings, making it difficult to accurately measure other analytes. Hemolysis can therefore lead to both overestimation and underestimation of various blood components, potentially resulting in misdiagnosis or inappropriate treatment.
Handling Hemolyzed Samples
When a blood sample arrives in the laboratory, it is first checked for hemolysis. This can be done visually, as hemolyzed samples have a distinct reddish tint, or through automated analyzers that detect free hemoglobin. If significant hemolysis is detected, especially for affected tests, the sample is often deemed unsuitable for analysis.
Laboratories typically have strict protocols for handling hemolyzed samples. Severely hemolyzed samples are frequently rejected, and the laboratory notifies the healthcare provider. A hemolyzed sample necessitates a re-draw, meaning the patient must undergo another blood collection procedure. This delay in obtaining accurate results can postpone diagnosis and the initiation of appropriate treatment.