Hemolysis is the breakdown of red blood cells, releasing their internal components into a blood sample. This changes the sample’s characteristics, potentially affecting laboratory analysis. To assess blood specimen quality, laboratories use the hemolysis index. Understanding this index helps ensure accurate and reliable test results.
What Is Hemolysis and Its Impact on Lab Samples
Hemolysis occurs when red blood cell membranes rupture, spilling their contents, primarily hemoglobin, into the plasma or serum. This released hemoglobin imparts a pink to red color to the normally pale yellow fluid. While some medical conditions can cause hemolysis within the body, most instances in laboratory samples result from pre-analytical issues.
Common reasons for hemolysis include improper sample collection, handling, or storage. Examples of these issues include vigorous shaking of the collection tube, drawing blood too quickly, or using a needle that is too small for the vein. A prolonged delay between collection and analysis can also contribute to red blood cell breakdown.
Hemolysis poses a significant challenge for laboratory testing because the released hemoglobin and other intracellular substances can interfere with various chemical and enzymatic assays. For instance, red blood cells contain much higher concentrations of potassium than plasma, so their rupture can falsely elevate potassium levels in the sample. Hemoglobin can also directly interfere with spectrophotometric measurements, where light absorption is used to quantify analytes. This interference can lead to inaccurate or unreliable results for numerous blood tests, making hemolysis the leading cause of sample rejection in many laboratories.
Understanding the Hemolysis Index
The hemolysis index quantifies free hemoglobin in a blood sample. Laboratories measure this index using automated analyzers that employ spectrophotometry. This method involves passing light through the sample and measuring how much is absorbed at specific wavelengths, such as 414 nm, 415 nm, 540 nm, or 571 nm, where hemoglobin absorbs light strongly.
The instruments calculate an index value based on these absorbance measurements. A higher index number indicates a greater degree of red blood cell breakdown and more free hemoglobin in the sample. While scales or thresholds may vary between laboratories or manufacturers, the index consistently indicates sample integrity and suitability for analysis. Modern analyzers often integrate these measurements with assessments for icterus (bilirubin) and lipemia (turbidity) to provide a comprehensive evaluation of sample quality.
Interpreting Hemolysis Index 0-24
A hemolysis index from 0 to 24 signifies minimal to no significant red blood cell breakdown. This range is acceptable for most laboratory analyses, indicating high sample quality and reliable results. Such low index values suggest proper collection and handling of the blood specimen.
When a sample’s hemolysis index falls within this range, interference from released cellular components is negligible for most common laboratory tests. While some very sensitive tests might be subtly affected, the impact is not considered clinically significant. This allows healthcare providers to confidently interpret the results without concern for substantial pre-analytical errors.
Conversely, if the hemolysis index is higher than 24, it means a greater concentration of free hemoglobin, which compromises test accuracy. For context, visible hemolysis (where plasma appears distinctly red) occurs when hemoglobin concentrations exceed 300 mg/L. Samples with elevated hemolysis indices may be flagged and often rejected, necessitating a new blood draw for accurate patient results.