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Prealbumin: Definition & Normal Range

Instructor: Jessica Franciosi
In this lesson you will learn about prealbumin and you will be able to determine if the amount present in a patient is normal. At the end of the lesson you can check your understanding with a quiz.

Prealbumin (TTR)

Before we discuss normal prealbumin values and why prealbumin is used as an assessment of malnutrition, we must first review where this protein is made in the body and what its responsibilities are.

Prealbumin, otherwise known as transthyretin (TTR), is a carrier protein made mainly in the liver. It is also made in the brain, specifically the choroid plexus, and in the retinal pigment epithelium in the eye. It binds with thyroxine (T4), which is the main hormone produced by the thyroid gland, and retinol-binding protein, which in turn binds with retinol, or Vitamin A.

Remembering the function of prealbumin (TTR) is simple: the name gives it away! Trans-Thy-Ret, or carrier (trans) of thyroid hormone (thy) and retinol (ret)! Prealbumin is normally found in your blood serum (the non-clotting, plasma part of blood), your cerebral spinal fluid, and your eyes. It has a relatively short half-life of about 2 days.

Clinical Relevance of Prealbumin

So why do we care about prealbumin, and how/why is it clinically relevant? It's relevant because of the short half-life, of course! The half-life of a substance is the time it takes for the concentration of that substance to fall to half its initial value. The short half-life of prealbumin makes it extremely sensitive to changes in the protein-energy status of the body. Albumin can't even come close to this type of accuracy; the half-life of albumin is somewhere around 20 days!

The importance of prealbumin in terms of energy requirements (think nutrition) is because of the liver, the main location where prealbumin is synthesized. Prealbumin is degraded, or starts to break down, as quickly as it's made owing to its short half-life. The breakdown inevitably leads to two clinically relevant effects: accumulation of prealbumin can't occur, and fluctuations in prealbumin levels are quickly detected.

Now that we've covered the science behind prealbumin, it's time to get to the point: Why exactly is a prealbumin blood test used?

It is time for your prealbumin blood test!
blood test

Prealbumin levels are used by your health care providers to assess acute malnutrition and nutritional deficiencies and to predict outcomes in malnourished patients. Prealbumin production decreases just two weeks after a protein-deficient diet is consumed. Usually, if you go two weeks with eating only 40% of the recommended protein, your prealbumin levels will drop. Conversely, prealbumin levels increase after a normal diet is resumed. Most importantly, the concentration of prealbumin in serum is a reflection of dietary intake rather than nutritional status; prealbumin is therefore a test of prognosis. Albumin is likely to be used as a determinant of chronic malnutrition owing to its longer half-life.

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