Serum albumin is a blood test that measures the levels of albumin, a protein produced by the liver, in the bloodstream. Albumin is an important protein that helps maintain the osmotic balance of fluids in the body and transports various substances, such as hormones, drugs, and fatty acids. The serum albumin test is commonly used to assess the nutritional status and liver function of an individual. Low levels of albumin in the blood may indicate malnutrition, liver disease, kidney disease, or other conditions that affect protein synthesis or increase protein loss.