All content on Lab Tests Online has been reviewed and approved by our Editorial Review Board.
The Test Sample
What is being tested?
Proteins are important building blocks of all cells and tissues; they are important for body growth, development, and health. They form the structural part of most organs and make up enzymes and hormones that regulate body functions. This test measures the total amount of the various types of proteins in the liquid (serum or plasma) portion of the blood.
Two classes of proteins are found in the blood, albumin and globulin. Albumin makes up about 60% of the total protein. Produced by the liver, albumin serves a variety of functions including as a carrier protein for many small molecules and ions, as a source of amino acids for tissue metabolism, and as the principle component involved in maintaining osmotic pressure (preventing fluid from leaking out of blood vessels).
The remaining 40% of proteins in the plasma are referred to as globulins. The globulin proteins are a varied group. They include enzymes, antibodies, hormones, carrier proteins, and numerous other types of proteins.
The level of total protein in the blood is normally a relatively stable value, reflecting a balance in loss of old protein molecules and production of new protein molecules.
Total protein may decrease in conditions:
- Where production of albumin or globulin proteins is impaired, such as malnutrition or severe liver disease
- That accelerate the breakdown or loss of protein, such as kidney disease (nephrotic syndrome)
- That increase/expand plasma volume (diluting the blood), such as congestive heart failure
Total protein may increase with conditions that cause:
Some laboratories report total protein, albumin, and the calculated ratio of albumin to globulins, termed the A/G ratio. The A/G ratio is calculated from measured total protein, 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. The A/G ratio may change whenever the proportions of albumin and other proteins shift (increase or decrease) in relationship to each other. 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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm or by a fingerstick (for children and adults) or heelstick (for newborns).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.