Albumin is the most abundant protein circulating in the human bloodstream, and its measurement is a common component of routine diagnostic blood work. Often appearing as “ALB” on a lab report, this protein is a primary indicator used by healthcare providers to assess the function of two major organ systems: the liver and the kidneys. Understanding albumin levels helps determine a person’s overall nutritional status and provides important clues about underlying health conditions, which is why abnormal results warrant further investigation.
What Albumin Is and Its Essential Functions
Albumin is a globular protein synthesized exclusively by the liver, which produces approximately 10 to 15 grams of it every day. This protein makes up about 50 to 60 percent of the total protein found in the liquid portion of the blood, known as plasma. Because it is so large, the albumin molecule generally cannot pass through the healthy walls of blood vessels.
One of albumin’s primary roles is maintaining oncotic pressure, also called colloidal osmotic pressure, within the circulation. This pressure is a pulling force that helps keep fluid inside the blood vessels and prevents it from leaking out into surrounding tissues. Without sufficient albumin, this fluid balance is disrupted, leading to swelling in the legs, abdomen, or other areas of the body.
Albumin also functions as a transport vehicle, binding to and carrying a wide array of substances through the bloodstream. It acts as a shuttle for hormones, such as thyroid hormones and cortisol, and transports minerals like calcium and magnesium. Many therapeutic drugs, fatty acids, and the waste product bilirubin are temporarily attached to albumin for safe passage and distribution throughout the body.
Diagnostic Testing for Albumin Levels
A healthcare provider may order an albumin test to investigate symptoms of liver or kidney disease, or to check for potential malnutrition. The most common form is the serum albumin test, which involves a simple blood draw and is frequently included as part of a comprehensive metabolic panel. This blood test provides a snapshot of the current concentration of albumin circulating in the plasma.
The serum albumin test serves as a broad indicator of liver function, as the liver must be healthy to manufacture the protein in sufficient quantities. It is also used to evaluate a person’s nutritional status, since inadequate protein intake can lead to lower production of albumin. A second, distinct test is the urine albumin test, sometimes called a microalbuminuria test, which is specifically ordered to screen for early kidney damage.
Healthy kidneys act as efficient filters, preventing large proteins like albumin from passing from the blood into the urine. However, when the filtering units in the kidneys become damaged, albumin begins to leak out, appearing in the urine before other, more severe symptoms emerge. The presence of even small amounts of albumin in the urine is considered an early sign of kidney disease, particularly in individuals with diabetes or high blood pressure.
Interpreting High and Low Albumin Results
The reference range for serum albumin is between 3.5 and 5.5 grams per deciliter (g/dL), though this may vary slightly between laboratories. Results outside this range can signal underlying health issues, with low albumin levels, known as hypoalbuminemia, being far more common and clinically significant than high levels.
Hypoalbuminemia is often caused by chronic liver disease, such as cirrhosis, where extensive scarring impairs the liver’s ability to synthesize the protein. It can also result from kidney disease, especially nephrotic syndrome, which causes the kidneys to excessively excrete albumin into the urine. Other causes include severe inflammation from chronic infections or inflammatory bowel diseases, protein-losing enteropathies, or malnutrition where the body cannot absorb or obtain enough protein.
High albumin levels, or hyperalbuminemia, almost always indicate that the blood is concentrated due to acute dehydration. When the total volume of fluid in the blood drops, the amount of albumin present stays the same, leading to a falsely elevated concentration reading. Certain medications, including high doses of steroids or insulin, can also influence a slight rise in albumin levels. If dehydration is ruled out, a result slightly above the normal range is rarely a cause for concern.