Plasma albumin, the most abundant protein in the bloodstream, makes up approximately half of the total protein content in healthy individuals. The liver synthesizes about 10 to 15 grams daily, releasing it into the bloodstream.
Regulating Fluid Distribution
Albumin plays a central role in maintaining the body’s fluid balance by exerting oncotic pressure, also known as colloid osmotic pressure. This pressure helps keep fluid within blood vessels, preventing leakage into surrounding tissues. Primarily albumin, plasma proteins generate this osmotic force due to their large size and negative charge, restricting their movement out of capillaries.
The constant interplay between hydrostatic pressure, which pushes fluid out of capillaries, and oncotic pressure, which pulls fluid back in, ensures proper fluid exchange and prevents excessive fluid accumulation in interstitial spaces. Without sufficient albumin, decreased oncotic pressure leads to an imbalance, allowing fluid to escape from the bloodstream. This can result in swelling, particularly in the legs, ankles, and feet, a condition known as edema.
Carrying Molecules Throughout the Body
Beyond its role in fluid balance, albumin functions as a versatile transport protein, carrying a diverse array of substances throughout the body. It binds to various endogenous molecules, such as fatty acids, thyroid and steroid hormones, and bilirubin, a waste product from red blood cell breakdown. This transport distributes these compounds to tissues where they are needed for energy, regulation, or elimination.
Albumin also transports numerous exogenous substances, including a wide range of medications. By binding to these drugs, albumin influences their distribution, activity, and how long they remain in the body. This binding can affect drug effectiveness and safety, making albumin levels relevant in medical treatment.
Acting as a pH Buffer
Albumin contributes to maintaining the stable pH of blood, acting as a buffer. It helps neutralize excess acids or bases by binding to or releasing hydrogen ions. This buffering capacity supports the overall stability of the internal environment, which is necessary for cellular and systemic health.
Impact of Abnormal Albumin Levels
Abnormal levels of plasma albumin can indicate underlying health issues. Low albumin levels, known as hypoalbuminemia, are more common than high levels. Hypoalbuminemia can result from decreased production by the liver, as seen in liver diseases like cirrhosis, or increased loss through the kidneys in conditions such as nephrotic syndrome. Malnutrition, severe inflammation, and certain infections can also contribute to low albumin.
The primary consequence of hypoalbuminemia is edema, where fluid leaks from blood vessels into tissues due to reduced oncotic pressure. This fluid accumulation can cause swelling in the extremities, abdomen (ascites), or around internal organs. Low albumin levels can also impair the transport of essential substances and drugs, affecting their delivery and effectiveness. Elevated albumin levels, known as hyperalbuminemia, are less common and most frequently caused by dehydration, which concentrates the protein in the blood. Other causes include high protein diets or chronic inflammation. Hyperalbuminemia typically resolves with adequate fluid intake.