Albumin is a protein made by the liver. A serum albumin test measures the amount of this protein in the clear liquid portion of the blood.
The ratio of albumin to globulin (A/G ratio) is calculated from measured albumin and calculated globulin (total protein - albumin). Normally, there is a little more albumin than globulins, giving a normal A/G ratio of slightly over 1. Because disease states affect the relative amounts of albumin and globulin, the A/G ratio may provide a clue as to the cause of the change in protein levels. A low A/G ratio may reflect overproduction of globulins, such as seen in multiple myeloma or autoimmune diseases, or underproduction of albumin, such as may occur with cirrhosis, or selective loss of albumin from the circulation, as may occur with kidney disease (nephrotic syndrome). A high A/G ratio suggests underproduction of immunoglobulins as may be seen in some genetic deficiencies and in some leukemias. More specific tests, such as liver enzyme tests and serum protein electrophoresis, must be performed to make an accurate diagnosis. With a low total protein that is due to plasma expansion (dilution of the blood), the A/G ratio will typically be normal because both albumin and globulin will be diluted to the same extent.
Globulins is the collective term for most blood proteins other than albumin. Identifying the types of globulins can help diagnose certain disorders. Globulins are roughly divided into three groups: alpha, beta, and gamma globulins. Gamma globulines include various types of antibodies such as immunoglobulins (Ig) M, G, and A.