Thyroxine-Binding Prealbumin (TBPA)

What sample is needed for Thyroxine-Binding Prealbumin?

1. The serum of the patient is needed.
2. Analyze the sample fresh or store it at 4 °C for <72 hours.
3. At -20 °C, the serum is stable for 6 months.
4. Avoid serum with lipemia or hemolysis.

What are the Indications for Thyroxine-binding prealbumin?

1. Transthyretin is advised to differentiate hyperthyroidism from hypothyroidism.
2. Genetic variants Transthyretin are associated with decreased or increased T4 and T3.
3. Prealbumin estimation Is advised to work up malnutrition.
4. Prealbumin is a better indicator of liver function than albumin.

How will you define the structure of Thyroxine-Binding Prealbumin (Transthyretin)?

1. Prealbumin is synthesized in the liver and is found in the blood and CSF.
2. Prealbumin is the fastest-migrating protein in serum electrophoresis. However, it is not seen on the electrophoresis, and there is a faint band.

3. Prealbumin binds the thyroxine, so-called thyroxine-binding prealbumin (TBPA).
   1. Thyroxine-binding prealbumin has a molecular weight of 50,000 D.
4. Transthyretin is known as prealbumin binding the thyroid hormones.
   1. Transthyretin is prealbumin that carries the thyroid hormones  (T4 and T3) in the blood and CSF.
   2. So, it transports thyroxine and retinol.

How will you interpret Thyroxin-binding prealbumin (Transthyretin)?

1. T4 and T3 are poorly soluble in the plasma, so they are transported by thyroglobulin and 15% by albumin and prealbumin.
2. The prealbumin transports 10% of thyroid hormones.

3. Thyroxine is 99% bound to Thyroid-binding globulin, albumin, and prealbumin.
   1. Transthyretin, known as prealbumin, has a half-life of 48 hours (1.9 days).
   2. This TBPA does not play a major role in thyroid hormone functions.
4. Prealbumin is secondary to thyroxine-binding globulin (TBG) for transporting T3 and T4.

How will you interpret Prealbumin?

1. Previously, albumin was the marker of malnutrition and is now replaced by prealbumin.
2. The albumin half-life is 21 days, while the half-life of prealbumin is 2 days (1.9 days).
   1. Its short half-life is the more sensitive indicator of any change affecting protein synthesis.
   2. This is the marker in the case of parenteral nutrition.
   3. There will be a marked decrease in the prealbumin level in liver diseases.
   4. Prealbumin is decreased in inflammation, malignancies, and protein-losing diseases of the kidneys and intestine, so it is a negative acute-phase protein reactant.
3. Prealbumin will be raised in Hodgkin’s lymphoma and chronic kidney diseases.
4. Prealbumin can cross the blood-brain barrier, so it is found in the CSF.

What is the normal Thyroxine-Binding Prealbumin (Transthyretin)?

Source 1

Transthyretin (Thyroxine-binding prealbumin)

Source 2
Normal Prealbumin level:

• Adult/elders = 15 to 36 mg/dL.
• Children <5 days = 6 to 21 mg/dL.
  • 1 to 5 years = 14 to 30 mg/dL.
  • 6 to 9 years = 15 to 33 mg/dL.
  • 10 to 13 years = 22 to 36 mg/dL.
  • 14 to 19 years = 22 to 45 mg/dL
• Urine = 0.017 to 0.047 mg/day
• CSF = roughly 2% of the total CSF protein.

What are the causes of increased Thyroxine-binding prealbumin (Transthyretin)?

1. In the case of high doses of corticosteroids.
2. Nonsteroidal anti-inflammatory drugs.
3. Hodgkin’s disease.
4. Adrenal hyperactivity.

What are the causes of decreased Tryroxin-binding prealbumin (Transthyretin)?

1. It is a very sensitive negative acute-phase protein. It may drop to <20% of the median level.
2. It falls during calorie-protein malnutrition.
3. It is also seen in several forms of hereditary amyloidosis.

Prealbumin

What are the causes of the increase in the level of Prealbumin?

1. Hodgkin’s disease.
2. Nephrotic syndrome (some of the cases).
3. Pregnancy.
4. Anabolic steroids, androgens, estrogen, and prednisone may increase the value.

What are the causes of decreased levels of Prealbumin?

1. Malnutrition.
2. Liver diseases.
3. Inflammation.
4. Burns.
5. Drugs may decrease the level of oral contraceptives and amiodarone.

• The critical value of prealbumin is <10.7 mg/dL, indicating severe malnutrition.