Blood plasma is the straw-yellow liquid matrix that transports various substances throughout the body, making up about 55% of the total volume of blood. This fluid is predominantly water, accounting for about 92% of its composition, allowing it to act as the primary medium for circulation. Plasma transports dissolved nutrients, hormones, proteins, and waste products like carbon dioxide, delivering them where they are needed or carrying them away for excretion. While whole blood is deep red due to red blood cells, the liquid portion separated from these cells has a distinct, lighter hue imparted by its dissolved components.
The Normal Appearance and Composition of Plasma
The expected and healthy color for plasma is a clear, light straw-yellow or amber. This subtle coloration is not caused by red blood cells, which have been separated out, but rather by substances naturally dissolved within the fluid. The most significant contributors to this normal yellow tint are plasma proteins, such as albumin, and trace amounts of circulating pigments like carotenes, which are absorbed from the diet. A healthy plasma sample should also be transparent, meaning it is clear enough to see through, and not cloudy or opaque.
When Plasma Appears Milky or Turbid
A cloudy, milky, or opaque appearance in plasma is a condition known as lipemia. This cloudiness occurs when there are excessive levels of circulating lipids, or fats, in the blood. Specifically, the largest fat-carrying particles, chylomicrons and triglycerides, are responsible for creating the turbid, light-scattering effect.
This condition can be transient, often resulting from a non-fasting blood draw following a recent meal high in fat content. Persistent or severe lipemia, referred to as pathological lipemia, can signal underlying metabolic disorders such as uncontrolled diabetes or certain genetic hyperlipidemias. The physical presence of this excess lipid can interfere with many common laboratory tests that rely on light absorption, potentially leading to inaccurate results.
When Plasma Appears Dark Yellow or Jaundiced
Plasma that presents with a deeper yellow, orange, or greenish-yellow hue is described as icteric, a finding strongly associated with jaundice. This intense coloration is caused by an abnormally high concentration of bilirubin circulating in the blood. Bilirubin is a yellow pigment that is a natural breakdown product of hemoglobin, released when old red blood cells are recycled.
Normally, the liver processes and excretes bilirubin, but a dark yellow plasma color suggests an issue with this process. The hyperbilirubinemia, or excess bilirubin, can be classified into three main categories based on the source of the problem.
Categories of Icterus
Prehepatic icterus occurs when red blood cells are destroyed too rapidly for the liver to keep up, such as in hemolytic anemia. Hepatic icterus points to liver cell dysfunction, where the organ cannot properly clear the normal bilirubin load due to diseases like hepatitis or cirrhosis. Posthepatic icterus results from a blockage, such as gallstones, that prevents the liver from excreting the processed bilirubin into the digestive system.
When Plasma Appears Pink or Red
A pink or red tint in plasma indicates the presence of free hemoglobin and is medically termed hemolyzed plasma. This color results from the rupture of red blood cells, a process called hemolysis, which releases their contents directly into the fluid. The degree of redness, ranging from a faint pink to a cherry-red, is proportional to the amount of hemoglobin released.
Hemolysis is frequently an artifact of the blood collection process, known as in vitro hemolysis. This can happen due to procedural errors like using too small a needle, vigorous shaking of the collection tube, or subjecting the sample to improper temperatures. Less commonly, hemolysis is in vivo, meaning it occurs within the patient’s body due to a medical condition. While laboratory-induced hemolysis primarily affects the accuracy of test results, in vivo hemolysis is a direct indicator of disease, often seen in hemolytic anemias or certain transfusion reactions.