Biomarker: Protein, Total

Overview

Total protein measures the combined concentration of albumin and globulins in the fluid portion of blood. These proteins help maintain fluid balance and transport substances, while globulins include antibodies and other proteins involved in immunity. High levels may occur with dehydration, chronic inflammation or infection, and some plasma-cell disorders; low levels may occur with liver disease, kidney disease, malnutrition, malabsorption, or protein loss. The test is clinically useful as a general assessment of nutritional status, fluid balance, and possible liver, kidney, or immune-system disorders, usually alongside other tests.

Clinical Use Cases

Evaluation of suspected liver disease, kidney disease, malnutrition, or malabsorption.
Assessment of abnormal fluid balance, including dehydration or overhydration.
Evaluation of abnormal albumin or globulin concentrations and the albumin-to-globulin ratio.
Part of a comprehensive metabolic panel or liver-function evaluation.
Follow-up testing when an initial result is abnormal.
Supportive evaluation for chronic inflammation, infection, or monoclonal protein disorders such as multiple myeloma, usually with additional testing such as serum protein electrophoresis.

Specimen Types

Serum, typically collected from venous blood.
Plasma, when validated by the testing laboratory.
Urine may be used for related protein testing, but it is not the usual specimen for routine total blood protein measurement.

Measurement Methods

Biuret colorimetric assay, the routine and reference method for serum or plasma total protein measurement.
Automated clinical chemistry analyzers using the biuret reaction.
Serum or plasma protein electrophoresis for separating and characterizing protein fractions, rather than measuring total protein alone.

Test Preparation and Influencing Factors

Fasting is generally not required for total protein alone, but fasting may be required when the test is included in a comprehensive metabolic panel or another test panel.
Tell the health care provider about all prescription medicines, over-the-counter medicines, vitamins, and supplements because some may affect results.
Do not stop or change medicines unless instructed by a health care provider.
Dehydration can increase the measured concentration through hemoconcentration, while overhydration or large-volume intravenous fluids can lower it through dilution.
Prolonged tourniquet application and changes from lying to sitting or standing can increase measured protein concentration; standardized collection conditions help reduce this variation.
Hemolysis and lipemia may interfere with measurement and may require specimen evaluation or recollection.
Pregnancy can increase total protein results.
Reference intervals vary by laboratory, age, and clinical context; results should be interpreted using the reporting laboratory’s range.