Prealbumin is a protein primarily synthesized by the liver. Its main function is to transport substances, such as certain hormones and vitamins, through the bloodstream. Because its levels can be measured with a blood test, physicians use it as a marker to gain insight into a person’s health, particularly their nutritional state.
The Role of Prealbumin in the Body
Prealbumin, also known as transthyretin, has two primary transport jobs in the body. It binds to and carries thyroxine, a thyroid hormone, and also transports vitamin A, in the form of retinol, throughout the bloodstream. This transport function prevents these smaller molecules from being filtered out of the blood by the kidneys.
A defining characteristic of prealbumin is its short half-life of about two days. This means that half of the prealbumin in the blood is broken down and replaced every 48 hours. This rapid turnover makes its measurement a sensitive indicator of a person’s protein and calorie status.
The quick response of prealbumin to nutritional changes distinguishes it from albumin, another protein made by the liver. Albumin has a much longer half-life of about 20 days, so its levels reflect a person’s nutritional history over several weeks, whereas prealbumin provides a snapshot of intake over the preceding days.
Understanding the Prealbumin Test
A physician may order a prealbumin test to assess a patient’s nutritional status, particularly in specific clinical scenarios. These situations include evaluating a patient before major surgery, monitoring individuals during extended hospital stays, or assessing those with chronic illnesses that impact nutrient absorption. The test is also used to see if nutritional support, like intravenous feeding, is effective.
The results of a prealbumin test are measured in milligrams per deciliter (mg/dL). A normal range for adults is between 15 to 36 mg/dL, though this can vary between laboratories, so it is important to interpret results based on the reference range provided by the lab.
Prealbumin levels are rarely interpreted in isolation because factors other than nutrition can influence them. For this reason, doctors often look at prealbumin in conjunction with a C-reactive protein (CRP) test, as inflammation can also cause prealbumin levels to drop.
Causes of Low Prealbumin Levels
Low prealbumin levels can stem from several underlying issues. The primary cause is protein-calorie malnutrition, which occurs when a person’s diet lacks sufficient protein and energy. This can be due to poor dietary intake, eating disorders, or conditions that increase nutritional requirements, such as recovering from a serious injury or surgery.
A second major cause of low prealbumin is significant inflammation or infection. During an inflammatory response, the liver reprioritizes protein production, decreasing the synthesis of proteins like prealbumin and increasing the production of acute-phase reactants like C-reactive protein. This is why a low prealbumin level accompanied by a high CRP level points toward inflammation as a significant factor.
Other conditions can also lead to decreased prealbumin. Severe liver disease is a direct cause, as a damaged liver cannot produce the protein effectively. Certain digestive disorders that lead to malabsorption, such as Crohn’s disease, can also result in low levels.
Causes of High Prealbumin Levels
Elevated prealbumin levels are encountered less frequently than low levels. A primary reason for an abnormally high reading is chronic kidney disease. When the kidneys are not functioning properly, they fail to adequately filter prealbumin from the blood, leading to an accumulation of the protein.
Another potential cause of high prealbumin is the long-term use of high-dose corticosteroid medications. These drugs can stimulate the liver to produce more of the protein. Other medications like anabolic steroids and androgens can also cause prealbumin levels to rise, and less commonly, conditions such as Hodgkin’s disease and alcoholism have been associated with elevated levels.
Managing Abnormal Prealbumin Levels
The management of abnormal prealbumin levels focuses on addressing the underlying cause, as the value itself is a marker, not a disease. A healthcare professional directs treatment based on a comprehensive evaluation of the patient’s condition. An improving prealbumin level is often a positive sign that the treatment for the primary health issue is effective.
For individuals with low prealbumin caused by malnutrition, the treatment involves nutritional support. This can range from dietary counseling and oral supplements to more intensive interventions like intravenous (IV) nutrition. If the low level is due to an infection or inflammation, treating that root cause is the priority.
When prealbumin levels are high, management centers on the condition causing the elevation. If chronic kidney disease is the culprit, treatment will be directed at managing the kidney dysfunction. If medication is identified as the cause, a physician may re-evaluate the treatment plan.