A blood test result may sometimes include the term “lipemic,” describing the appearance of the blood sample after processing. Lipemic refers specifically to excessive lipids, or fats, in the blood plasma or serum, primarily triglycerides and lipoproteins. A lipemic sample indicates a high concentration of these fatty substances, typically becoming noticeable when triglyceride levels exceed a certain threshold. This condition is recognized by laboratory professionals because it can directly interfere with the methods used to analyze the sample.
The Science of Lipemia and Its Appearance
In a laboratory setting, blood is spun in a centrifuge, separating cellular components from the liquid portion (serum or plasma). A normal, non-lipemic sample of serum or plasma appears clear and light straw-yellow. When a sample is lipemic, however, this liquid layer takes on a visibly cloudy, opaque, or milky-white appearance.
This visual change is caused by the high concentration of large lipid particles, mainly chylomicrons and very low-density lipoproteins (VLDLs). These particles are large enough to scatter the light passing through the sample, a phenomenon known as turbidity. The resulting milkiness, sometimes described as “lactescence,” is a physical manifestation of the fat load in the patient’s blood. Labs typically flag a sample as lipemic when triglyceride levels are above 3.4 mmol/L (300 mg/dL).
Factors That Cause Lipemic Blood Samples
Lipemia is generally categorized into two causes: temporary (dietary) and chronic (related to an underlying medical condition). The most frequent reason for a lipemic sample is failing to fast before the blood draw. Consuming a meal, especially one high in fat, causes a temporary spike in chylomicrons as the digestive system processes the fat.
This post-meal lipemia usually peaks a few hours after eating and then gradually clears from the bloodstream. Persistent or severe lipemia, however, often points to a chronic medical issue, known as hypertriglyceridemia. Conditions such as uncontrolled diabetes mellitus, certain liver diseases, or inherited genetic disorders can lead to consistently high levels of fat in the blood. In these cases, the elevated lipids are a continuous metabolic issue, not just a temporary post-meal effect.
How Lipemia Affects Lab Test Accuracy
The presence of excess lipids significantly affects the accuracy of many laboratory tests by interfering with analytical instruments.
Spectrophotometric Interference
One major mechanism is spectrophotometric interference, where the milky turbidity scatters the light beams used by automated analyzers. Since many tests measure substance concentration based on how much light it absorbs, this scattering can lead to falsely high or low readings. This interference affects various analytes, including bilirubin and certain proteins.
Volume Displacement (Solvent Exclusion)
Another interference mechanism is volume displacement, or solvent exclusion. In a normal blood sample, the water phase makes up about 92% of the plasma volume, dissolving electrolytes. When the lipid phase is excessive, it physically displaces the water volume, reducing the proportion of water in the overall sample. Methods measuring electrolyte concentration (e.g., sodium) in the total volume report a falsely low result because the water concentration appears diluted. When a sample is severely lipemic, the laboratory may need to dilute the sample, run specialized tests, or request a redraw to ensure accuracy.
Preparing for a Blood Test to Avoid Lipemia
Patients can take specific steps to prevent dietary lipemia and ensure accurate blood test results. The standard method for preventing temporary lipemia is fasting for a specific duration before the blood draw. For many common tests, this involves abstaining from food and calorie-containing beverages for 10 to 12 hours.
Patients are generally allowed to drink water during fasting but must follow all specific instructions regarding medication and alcohol intake. Adhering to the fasting protocol clears temporary chylomicrons from recent meals, preventing turbidity that interferes with analysis. If a patient fasts correctly and the sample remains lipemic, this signals the possibility of an underlying metabolic disorder requiring further medical investigation.