Total protein is a laboratory parameter that reflects the total concentration of all proteins in blood serum. They are involved in blood clotting and metabolic processes, perform transport functions, and help maintain the acid-base balance of the blood. A total protein test allows assessment of the proteins circulating in the blood and is used as part of the comprehensive evaluation of liver and kidney diseases, metabolic disorders, and other conditions.
The main groups of serum proteins are albumin and globulins.
Total protein is the combined concentration of albumin and globulins in serum. Albumin accounts for the largest proportion of total protein and is produced by the liver.
Globulins include antibodies, transport proteins, enzymes, and other compounds. Some of these proteins are produced in the liver, while antibodies are produced by cells of the immune system.
Blood Protein: Main Functions
Proteins circulating in the blood:
- help maintain the normal distribution of fluid between blood vessels and tissues;
- transport hormones, bilirubin, fatty acids, and certain medications;
- participate in immune defense;
- help maintain the acid-base balance of the blood;
- function as enzymes and other substances that regulate processes in the body;
- certain proteins are involved in blood clotting.
The term protein is also used to refer to this substance. However, this test does not measure the amount of protein consumed in the diet and does not directly assess protein stores in muscles or other tissues.
Total protein levels are affected by protein production and loss, nutrition, nutrient absorption, and the amount of fluid in the blood. A laboratory
The result is used as part of a comprehensive diagnostic evaluation. A single total protein result cannot determine the cause of an abnormal level. Depending on the purpose of the evaluation, a physician may additionally order albumin testing, the albumin-to-globulin ratio, testing of protein fractions, liver and kidney function tests, or a urine protein test.
Total Protein: Reference Range
The term ‘normal total protein’ refers to the reference range – the range against which the test result is compared. In adults, the approximate total protein level is 66-87 g/L. Separate age-specific reference ranges are used for children.
The reference range may vary depending on the testing method and laboratory equipment, so the values provided on the laboratory report should be used as the primary reference. Interpretation also takes into account albumin levels, liver and kidney function, nutrition, and the amount of fluid in the body.
Causes of High Total Protein Levels in the Blood
A high blood protein level is often associated not with excessive protein production but with a reduced amount of fluid in the blood. This may occur with inadequate fluid intake, prolonged vomiting, diarrhea, significant burns, or other conditions accompanied by fluid loss. In such cases, the blood becomes more concentrated, causing the total protein level to appear relatively elevated.
Other possible causes include:
- acute or chronic infectious and inflammatory diseases;
- autoimmune diseases, in which the immune system mistakenly reacts against the body's own tissues;
- certain chronic liver diseases associated with increased globulin levels;
- excessive production of antibodies or other proteins by the immune system;
- certain diseases of the blood and bone marrow in which large amounts of a particular type of protein are produced.
Causes of Low Total Protein Levels in the Blood
A low total protein level may occur when the body produces fewer proteins, does not receive or absorb enough protein from the diet, loses protein, or breaks it down more rapidly.
Possible causes include:
- inadequate or unbalanced nutrition;
- impaired nutrient absorption due to diseases of the stomach, intestines, or pancreas;
- severe or prolonged liver disease, which reduces protein production;
- kidney diseases associated with urinary protein loss;
- protein loss through the gastrointestinal tract;
- significant bleeding, burns, extensive wounds, or other tissue injuries;
- severe infections, inflammatory diseases, and conditions associated with increased protein breakdown;
- excessive fluid intake, including during the intravenous administration of a large volume of fluid.
During pregnancy, total protein levels may also decrease slightly due to an increase in the volume of the fluid component of the blood. This change does not always indicate disease, but the result should be interpreted in relation to the stage of pregnancy and other laboratory findings.
Low total protein, particularly when accompanied by low albumin, may be associated with edema, weakness, weight loss, or slower wound healing.
