Total Protein — Vet Nursing Education
Terminology
A total protein (TP) assay is a measurement of the proteins found in plasma (the liquid portion of the blood). The majority of plasma proteins are produced by the liver (Sirois, 2015).
If a plasma sample is used to obtain the TP result then it will contain fibrinogen values. Whereas if a serum sample is used the TP result will be slightly lower, as the fibrinogen was removed during the clotting process. From a patient care point of view this difference is too small to make any meaningful change to the treatment of the case. It is just important for you to be aware of this difference and note whether the TP result was based on a serum or plasma sample.
Serum is obtained when a blood sample is placed in a plain tube. The lack of anticoagulant means that the blood will clot, separating the serum from the clump of blood cells, platelets and fibrinogen within the sample tube. The sample can be centrifuged to push the clot to the bottom of the container and make it easier to draw off the serum for testing without disturbing the clot and thereby contaminating the sample.
If the blood is collected into a container with an anticoagulant such as lithium heparin, the fibrinogen will remain suspended within the plasma. No clot will form and the sample will have to be centrifuged to separate the plasma from the blood cells. The exception to this is equine blood – the blood cells in this species are heavy enough that they will settle in the bottom of the tube if it is left to stand in a rack before testing.
Visual evaluation
Visual examination of the plasma or serum before testing can detect some abnormalities:
Normal: clear, straw-yellow liquid (horses normally have slightly darker plasma/serum than other species).
Deep yellow/orange: jaundice, liver disease or haemolysis.
Red: haemolysis, either due to clinical disease or poor sample collection and/or storage, aged samples.
Milky white: lipaemia, due to a recent or high-fat meal, liver disease, pancreatic disease.
