Prealbumin (As a Acute phase protein)

Prealbumin

Sample

1. The venous blood of the patient is needed to prepare the serum.
2. This can be estimated in the 24 hours of urine and CSF.

Indications

1. Marker for the patient with nutritional status.
2. It is a sensitive indicator of protein synthesis and catabolism.

Precautions

1. If there is co-existent inflammation, then test result interpretation is not possible.
2. Drugs increasing the level are anabolic steroids, androgens, estrogens, and prednisolone.
3. Drugs that may decrease the level are amiodarone, estrogens, and oral contraceptives.

Pathophysiology

1. In 1995, the joint committee on Accreditation of health organization first issued the main parameter to assess the patient nutritional status, to identify all patients with malnutrition.
   1. For a long time albumin was the parameter for the nutritional status (malnutrition). Now it is found that prealbumin is the better choice because of the short half-life of 1.9 days.
2. Prealbumin is one of the major proteins.
3. Prealbumin has a shorter half-life of 2 days (1.9 days).
   1. Prealbumin half-life of 2 days is much less than the albumin of 21 days.
   2. Because of its short half-life, prealbumin is a better indicator of synthesis and catabolism.
   3. This is usually indicated to monitor the effectiveness of parenteral nutrition therapy.
4. This is present in the serum and CSF.
   1. This is the main component of the CSF proteins. It can cross the blood-brain barrier, so it is secreted into the CSF by the choroid plexus.
   2. Prealbumin is the faster-migrating protein on the serum electrophoresis. Because of the less amount, it is not seen on the traditional serum electrophoresis.
   3. But this is seen in the CSF protein electrophoresis.
   4. The purpose of CSF electrophoresis is to diagnose multiple myelosclerosis by finding the oligoclonal band.
5. Functions:
   1. The pre-albumin binds and transport:
      1. Prealbumin binds retinol-binding protein (RBP), which in turn binds vitamin A.
      2. It plays role in the transport and metabolism of vitamin A. This protein-vitamin complex formation is necessary to transport the oil-soluble vitamin A through the body.
      3. Prealbumin sometimes referred to as thyroxine-binding prealbumin (TPA). It does not play a major role in thyroid hormone functions.
      4. It binds T3 and T4, so it is also called transthyretin and thyroxine-binding prealbumin (TBPA).
      5. Mainly there is the secretion of the T4 and only about 7% is T3. In the blood >99% of T4 and T3 are bound to serum proteins. About 80% to 85% of T4 is bound to T4-binding globulin (TBG), and α-1 globulin;  about 10% to 15% to prealbumin.
         

         T4 binding proteins

6. Importance of the prealbumin:
   1. Prealbumin levels in the serum fluctuate more rapidly in response to the synthesis rate, in comparison to other serum proteins.
   2. Because of this property, prealbumin is a useful indicator of nutritional status.
   3. Prealbumin decreases in hepatobiliary diseases because of impaired synthesis.
   4. The serum level of prealbumin is a better indicator of liver synthetic function than albumin.
   5. Zinc is needed for the synthesis of prealbumin, so in case of deficiency of zinc, there will be a low level of prealbumin.
   6. The increased level was seen in Hodgkin disease and chronic kidney diseases.
7. This is a good marker than albumin and transferrin.
8. This is a better indicator of liver synthetic activity.
9. Prealbumin is the precursor of the amyloid in senile cardiac amyloidosis.
10. A mutant version of prealbumin (transthyretin) is responsible for familial amyloid polyneuropathy.

The severity of malnutrition:

The severity of the malnutrition	Prealbumin level
Mild	10 to 15 mg/dL (100 to 150 mg/L)
Moderate	5 to 10 mg/dL (50 to 100 mg/L)
Severe	0 to 5 mg/dL (0 to 50 mg/L)

1. Prealbumin is a negative acute-phase reactant protein.
   1. Its level decreases in malignancy, and inflammation.
   2. Also, it is decreased in the protein-losing diseases of the intestine and kidneys.
2. Prealbumin because of the small quantity in the blood, may not be detected on serum electrophoresis. As it can cross the blood-brain barrier, so may be found in the CSF electrophoresis.
3. The medicolegal and medical importance of prealbumin:
   1. The absolute concentration of the prealbumin in CSF and serum is the same. because of the low level of other proteins, prealbumin is the major protein in the CSF.
   2. So prealbumin can be used as a marker when there is leakage of the fluid from the nose or from the fracture of the skull.
   3. Prealbumin will differentiate nasal secretion from the leakage of CSF from the brain.

Normal values of prealbumin

Age	Normal range
Adults/elders	15 to 36 mg/dL (150 to 360 mg/L)
<5 years	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 24 hours sample	0.017 to 0.047 mg/day
CSF	Approximately 2% of the CSF total proteins
Critical value	<10.7 mg/dL (indicate severe malnutrition)

Another source of prealbumin

• 19 to 38 mg/dL ( 190 to 380 mg/L) by nephelometry.

The decreased level of prealbumin is seen in:

1. In hepatocellular dysfunction. There is a diminished synthesis of prealbumin.
2. It is decreased in tissue damage.
3. In inflammation. As it is a negative acute-phase protein, so its level will decrease in the inflammatory conditions.
4. In malnutrition.
5. In burn, there is acute loss of protein from the burn area.
6. Drugs like oral contraceptives, Estrogen, and amiodarone.
   1. Salicylates poisoning.

The increased level of prealbumin is seen in:

1. In Hodgkin’s disease.
2. In chronic kidney diseases.
3. Some cases of nephrotic syndrome.
4. In pregnancy
5. Drugs like steroids, prednisolone, and androgens.
6. Chronic alcoholics.

• Critical value = when <10.7 mg/dL
  • This indicates severe nutritional deficiencies.

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