Back Blood-tests Explained

A/G Ratio

At a Glance

Why Get Tested?

As part of a general health checkup, to determine your nutritional status or to screen for and help diagnose certain liver and kidney disorders as well as other diseases

When to Get Tested?

When you have a routine physical exam or when you experience unexpected weight loss or fatigue, or when a healthcare practitioner thinks that you have symptoms of a liver or kidney disorder

Sample Required?

A blood sample drawn from a vein in your arm or by fingerstick (adults and children) or heelstick (newborns)

Test Preparation Needed?

None

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:

Abnormally high production of protein (e.g., inflammatory disorders, multiple myeloma)
Dehydration

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).

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?
When is it ordered?
What does the test result mean?
Is there anything else I should know?

How is it used?

Total protein and albumin tests are routinely included in the panels of tests performed as part of a health examination, such as a comprehensive metabolic panel (CMP), so they are frequently used to help evaluate a person's overall health status.

Additionally, since total protein can be low, increased, or the component globulin proteins altered with many different diseases and disorders, total protein and albumin tests may be ordered in a variety of settings to help diagnose disease, to monitor changes in health status, and as a screen that may indicate the need for various follow-up tests.

(For more information about proteins in the blood, see the "What is being tested?" section.)

Total protein measurements can reflect nutritional status and may be used to screen for and help diagnose kidney disease or liver disease, for example. Sometimes conditions are detected with routine testing before symptoms appear. If total protein is abnormal, further testing must be performed to identify which specific protein is abnormally low or high so that a specific diagnosis can be made. Some examples of follow-up tests include protein electrophoresis and quantitative immunoglobulins.

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). 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.

When is it ordered?

A total protein test is frequently ordered as part of a comprehensive metabolic panel (CMP) when an individual undergoes a routine health checkup. Total protein may also be ordered to provide general information about a person's nutritional status, such as when someone has undergone a recent, unexplained weight loss. It can be ordered along with several other tests to provide information when someone has symptoms that suggest a liver, kidney, or bone marrow disorder, or to investigate the cause of abnormal pooling of fluid in tissue (edema).

What does the test result mean?

Results of a total protein test are usually considered along with those from other tests of the CMP and will give the healthcare practitioner information on a person's general health status with regard to nutrition and/or conditions involving major organs, such as the kidney and liver. However, if results are abnormal, further testing is usually required to help diagnose the disease affecting protein levels in the blood.

A low total protein level can suggest a liver disorder, a kidney disorder, or a disorder in which protein is not digested or absorbed properly. Low levels may be seen in severe malnutrition and with conditions that cause malabsorption, such as celiac disease or inflammatory bowel disease (IBD).
A high total protein level may be seen with chronic inflammation or infections such as viral hepatitis or HIV. It also may be associated with bone marrow disorders such as multiple myeloma.
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.
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.

Following an abnormal total protein result and depending on the suspected cause, more specific tests are typically performed to make an accurate diagnosis. Some examples include liver enzyme tests, renal panel, serum protein electrophoresis, or tests for celiac disease or IBD.

Is there anything else I should know?

Prolonged application of a tourniquet during blood collection can result in a blood sample with a falsely elevated total protein (higher than the actual concentration in the circulation).

Drugs that may decrease protein levels include estrogens and oral contraceptives.

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