Thyroxine Binding Prealbumin

Sample 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.

Purpose of the test (Indications)

1. Transthyretin is advised to differentiate hyper or 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.

Definition 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. But not seen on the electrophoresis, and there is a very 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.

Thyroxin binding prealbumin (Transthyretin) interpretations:

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

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.

Prealbumin interpretations:

1. Previously albumin was the marker of malnutrition 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 will be decreased in inflammation, malignancies, and protein-losing diseases of the kidneys and intestine, so this 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.

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.

Increased Thyroxine-binding prealbumin (Transthyretin) seen in:

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

Decreased Tryroxin-binding prealbumin (Transthyretin) seen in:

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.

Increase the level of Prealbumin seen in:

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

Decreased level of Prealbumin seen in:

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.

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