Formally called the transthyretin test, the prealbumin test (abbreviated the PA test) is a specific clinical indicator of nutritional risk for patients suffering from such diseases as cancer, CHF (congestive heart failure), diabetes, COPD (chronic obstructive lung disease), HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome), pneumonia, and renal disease. The PA test is also used to monitor patients at risk for poor nutrition and malnutrition.
Prealbumin is considered an important protein found in blood. The concentration of prealbumin (also called tryptophan-rich prealbumin (TRPA) and thyroxine-binding prealbumin [TBPA]) in blood plasma or serum is a reliable way to assess the nutritional status of patients (see nutritional assessment). The prealbumin test uses the well-established technique called turbidimetric immunoassay to measure the concentration of prealbumin in blood plasma or serum. The technique involves mixing a blood sample with assay reagents. The prealbumin binds specifically with an anti-human prealbumin antibody to produce an insoluble aggregate. The results produce increased turbidity (cloudiness) in the mixture. The degree of turbidity is directly proportional to the prealbumin concentration in the sample. The turbidity can then be measured with an clinical analyzer.
The prealbumin test is commonly used to measure the nutritional status of hospitalized patients because its results are reliable, fast, and accurate. Specifically, a patient should be given the prealbumin test when the physician suspects malnourishment due to poor diet, disease, being fed with intravenous nutrition, or being on hemodialysis. External signs of malnutrition include: inability to think or speak clearly, fainting spells, unusually large weight loss, declining resistance to infection, brittle, dry, and sometimes falling out hair, dry or yellowish skin, deteriorating muscles, stunted growth in a child, and stopped menstrual periods in women (amenorrhea). Patients who are more likely to receive the PA test are those who:
- are newly-admitted to a medical facility (especially scheduled for surgery)
- over 65 years of age
- unable to swallow or ingest food for five days
- chronically ill
- present with certain serious diseases and conditions
- have a history of loss of over 20% of body weight
- have a serum albumin level of less than 3.2 mg/dL
- hare placed on total or partial parenteral nutrition or external support.
The test also helps physicians diagnose specific problems with protein-energy malnutrition (PEM). In this condition, which according to recent studies can affect 30-50% of hospitalized patients, the body breaks down muscles, proteins, and body fats. This type of malnutrition, when not treated promptly, can lead to serious complications and death.
Proper nutrition before surgery helps to minimize complications such as pneumonia and infection after surgery. Numerous scientific studies have shown that malnutrition can lead to reduced quality of care in patients, higher mortality and morbidity, reduced wound healing, weakened mechanisms for fighting infections, and increased medical and pharmaceutical costs. Nutritional testing on incoming patients to hospitals can help to increase their quality of care. The prealbumin test is a proven and reliable way to test for nutrition.
There are no precautions necessary before taking the prealbumin test.
The PA test is a simple blood test. A health professional takes a blood draw with a needle from the patient's vein in the arm or wrist.
The test is given to measure levels of prealbumin. Prealbumin has a half-life of about 1.9 days, which means that the amount diminishes rapidly in the body. This short period helps doctors to quickly acquire a series of readings of a patient's nutrition with respect to the level of prealbumin in the blood. Physicians can monitor the patient much more effectively with the use of this test because they see results within two days, as opposed to 21 days (for example) with albumin, another nutritional marker. The PA test should be given two to three times per week. The results should be reviewed by the patient's physician and a dietitian.
The patient should inform the health professional, before the test is performed, about any inflammation present in the body. Inflammation can cause the PA test to be lower than normal. Drugs such as amiodarone, estrogen drugs, and oral contraceptives (birth control pills) can also produce lower-than-normal results. Hemodialysis patients generally receive inaccurate results.
There is no aftercare with the prealbumin test.
There are no complications expected with the prealbumin test.
A normal reading for the prealbumin test indicates a normal state of nutrition for the patient. A normal range is from 177-40 mg/dL. The maximum value is usually no more than 60 mg/dL. If prealbumin is low, various proteins and other substances in the blood may be low. If the test indicates an extremely low reading, then the patient may be extremely malnourished, prompting immediate medical care. Abnormally low levels are strong indications of severe or chronic illnesses such as digestive disorders, hyperthyroidism, liver disease, or serious infections. Abnormally high readings from the PA test indicate patients with high-dose corticosteroid therapy, high-dose non-steroidal anti-inflammatory medications, Hodgkin's disease, or hyperactive adrenal glands.
The accuracy of the PA test is less affected (when compared with other testing methods) by changes in hydration of the patient, along with being less dependent on liver and renal function.
Amiodarone— Antiarrhythmic agent used in the treatment of ventricular arrhythmias.
Assay Reagent— Sample reacting chemical.
Hemodialysis— Artifical process that filters and cleans blood.
Hodgkin's disease— Cancer of the lymphatic system.
Parenteral— Administering of drugs other than by mouth or rectum.
Plasma— Fluid part of blood.
Serum— Liquid part of blood.
Health care team roles
A health professional will administer the blood draw on the patient. The patient's physician will advise the patient as to the results of the test and a dietician, if necessary, may recommend special dietary measures.
In a medical center or hospital, a nutritional support team should consist of one or more of the following professionals: laboratory technicians, dietitians, pharmacists, nurses, and physicians. This team should be on staff to determine and ensure the nutritional health of its patients.
Shannon, Joyce Brennfleck, editor. Medical Tests Sourcebook: Basic Consumer Health Information about Medical Tests. Detroit, MI: Omnigraphics, 1999.
Shtasel, Philip. Medical Tests and Diagnostic Procedures: A Patient's Guide to Just What the Doctor Ordered. New York: HarperPerennial, 1991.
Lab Tests Online®, American Association for Clinical Chemistry. "Prealbumin." May 18, 2004. 〈http://www.labtestsonline.org/understanding/analytes/prealbumin/test.html〉 (December 5, 2005).