Prealbumin (PAB)

Sample

1. This is done on the fresh serum of the patient.
2. 24 hours of the urine sample can also be tested.

Indications

1. It is used to assess nutritional status.
2. As workup in patients with kidney diseases.
3. Advised in subclinical deficit and assessing the response to restorative therapy.

Precautions

1. In the case of inflammation, the result is not representative of the disease.
2. Drugs like anabolic steroids, androgens, and prednisolone increase the level.
3. Drugs like estrogens and oral contraceptives decrease the level.

Pathophysiology

1. Prealbumin is synthesized mainly in the liver.
   1. This was also called transthyretin because of its binding with thyroid hormones.
2. This is the fastest moving protein on the serum electrophoresis.
3. This has the same concentration in the serum and CSF. Due to the low level of other proteins in the CSF, prealbumin is the major protein in the CSF.
   1. This can be used to differentiate CSF leakage from the nasal secretions and the fracture of the base of the skull.
4. There is a very faint band so normally not seen on the traditional electrophoresis.
   

   Prealbumin shows the very faint band on serum Electrophoresis

5. Prealbumin is a carrier protein:
6. It binds to T3 and T4 so-called Transthyretin or thyroxine-binding prealbumin.
   1. This is also referred to as thyroxine-binding prealbumin (TBPA).
      

      T4 binding proteins and share of prealbumin

7. It also binds and carries retinol as a retinol-binding protein which in turn binds Vitamin A.
   1. This protein-vitamin complex is essential to transport oil-soluble Vitamin A in the body.
   2. Zinc is required for the synthesis of prealbumin, low levels occur in Zinc deficiency.
      

      Prealbumin as a transport carrier

7. Functions of prealbumin:
8. This is also the amyloid precursor protein and found in cardiac amyloidosis.
9. It has a half-life of 48 hours (1.9 days) which increases its importance superior to Albumin and transferrin.
   1. Albumin’s half-life is 21 days.
   2. Prealbumin is a very good indicator of any change affecting protein synthesis and catabolism.
   3. Because of its short half-life (2 days), prealbumin responds quickly to nutritional intake and nutritional restoration.
   4. It gives the current nutritional status of the body, not the status from 3 weeks ago.
10. It can cross the blood-brain barrier and actively secrete into the cerebrospinal fluid and choroid plexus.
    1. Importance of prealbumin in the nasal secretions to differentiate fluid coming from the skull fracture versus nasal secretion.
11. Negative acute-phase protein:
    7. Prealbumin is a negative acute-phase protein, and serum level decreases in inflammation, malignancy, and protein-losing diseases of kidneys and intestine.
12. Protein status of the patients by estimation of prealbumin:
    

    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)

Normal level of prealbumin

Source 2

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

Source 4

Prealbumin

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

Interpretations

•  In severe protein deficiency =  level is 0 to 5 mg/dl.
• In moderate protein deficiency =  level is 5 to 10 mg/dl.
• In mild protein deficiency = level is 10 to 15 mg/dl.

• (Normal value may vary from lab to lab.)

The increased level is seen in :

1. Chronic Alcoholics.
2. Patients with corticosteroid therapy.
3. Hodgkin’s lymphoma.
4. Kidney diseases.
5. Pregnancy.

The decreased level is seen in:

1. In cases of malnutrition.
2. Hypothyroidism
3. Liver diseases.
4. Inflammatory conditions.
5. In cases of trauma like burns.
6. In chronic diseases.
7. In some digestive diseases.
8. In Cancers.
9. Salicylate poisoning.

---