Blood plasma is the liquid medium that makes up approximately 55% of total blood volume. This aqueous matrix serves as the primary transport system for substances, carrying blood cells in suspension. Plasma is composed mostly of water, containing dissolved proteins like albumin, electrolytes, hormones, and waste products. Its continuous circulation delivers nutrients and chemical messengers to tissues while simultaneously removing cellular waste for excretion.
What Healthy Plasma Looks Like
When blood cells are removed from a sample, the plasma that remains is typically a pale yellow or straw-colored liquid. This slight coloration is the expected and healthy appearance, indicating the normal concentration of dissolved components. The yellow tint primarily comes from small amounts of bilirubin, a pigment produced during the breakdown of old red blood cells. Trace amounts of dietary pigments, such as carotenes found in vegetables, also contribute to this subtle hue.
When Plasma Turns Deep Yellow
A significant darkening of the plasma to a deep yellow, orange, or brownish-yellow color is known as icteric plasma. This dramatic change is a direct visual cue of hyperbilirubinemia, an excessive buildup of bilirubin in the bloodstream. Bilirubin is formed when the heme component of hemoglobin is metabolized, and the liver is responsible for processing and eliminating it.
When the liver is damaged or the bile ducts are obstructed, bilirubin cannot be effectively cleared, causing its concentration to rise dramatically. Elevated levels may signal underlying conditions like hepatitis, cirrhosis, or gallstones blocking bile flow. Excessive red blood cell destruction, such as in hemolytic anemia, can also overwhelm the liver’s capacity to process the pigment. The plasma color provides an immediate indicator that a patient’s total bilirubin level is likely well above the normal range.
Other Significant Color Variations
Beyond the deep yellow color, two other major variations offer important diagnostic information: milky and red plasma. A cloudy, opaque, or milky-white appearance is referred to as lipemia, which occurs due to an unusually high concentration of lipids, or fats. These fat particles, primarily large lipoproteins called chylomicrons and triglycerides, scatter light, causing the plasma to look turbid or creamy.
Lipemia can often be temporary, resulting from consuming a high-fat meal shortly before a blood draw, a state known as postprandial lipemia. However, persistent lipemia can be indicative of underlying metabolic disorders or uncontrolled diabetes. The other significant variation is a pink or reddish tint, which is caused by hemolysis, the rupture of red blood cells.
When red blood cells break open, they release their internal contents, mainly the red protein hemoglobin, directly into the surrounding plasma. This can happen in vitro (outside the body) due to improper sample collection techniques like using too narrow a needle or vigorous shaking of the blood tube. Alternatively, a pinkish color can signal in vivo hemolysis, indicating a medical condition causing red blood cells to break down prematurely. Both lipemia and hemolysis can interfere with the accuracy of many common laboratory tests, often requiring a new, high-quality sample.