Generality
Transthyretin (TTR) is a protein synthesized mainly by the liver, formerly defined as prealbumin (due to its greater electrophoretic mobility compared to albumin, which allows it to migrate to a more anodic position). The new term. Transthyretin. Takes on a functional meaning. , since the protein acts as a plasma transporter of thyroxine and retinol (which it indirectly conveys by equimolecular bond with the RBP: retinol binding protein).
Besides carrying thyroid hormones (thyroxine and triiodothyronine) in the blood, transthyretin, also synthesized by the chorioid plexus, carries them inside the cerebrospinal fluid.
Transthyretin has a short half-life (2-3 days), which makes it ideal as a marker of nutrition status; since its synthesis does not depend on the state of health of the liver, except in cases in which this is seriously compromised, prealbumin or transthyretin is an ideal marker for evaluating the nutritional status of the subject, also in response to therapeutic interventions.
As mentioned, low levels of transthyretin are typical of calorie-protein malnutrition and may depend on conditions in which there are protein deficiencies due to reduced dietary intake (KwashiorKor), poor absorption (enteropathies, celiac disease) or increased catabolism (febrile states, cachexia) , AIDS, neoplasms, hyperthyroidism, hypercortisolism or Cushing's syndrome). Transthyretin deficiency can also be detected in severe liver disease, such as advanced cirrhosis.
What's this
- Transthyretin (also known as prealbumin due to its electrophoretic characteristics) is a protein synthesized mainly by parenchymal cells of the liver. Small amounts of this protein are also produced by the chorioid plexus, pancreas and retina.
- Prealbumin is mainly catabolized in the liver and eliminated in the kidney and gastrointestinal tract. Its half-life is approximately 2-3 days.
- The synthesis of prealbumin is influenced by some pro-inflammatory cytokines; therefore, during the inflammatory response of the acute phase, its blood concentrations decrease.
Because it is measured
Transthyretin testing (TTR) is used as an indicator of nutritional status, in supporting the diagnosis of malnutrition and in monitoring the efficacy of parenteral or hemodialysis therapy.
At present, the reasons for the use of the test and its possible clinical usefulness are being updated. In the course of certain inflammatory pathologies, significant changes in blood transthyretin have in fact been observed.
Normal values
The serum concentration of transthyretin is low during fetal life and in the newborn, it slowly rises to a peak during the fifth decade of life, after which the circulating quantities decrease.
Reference ranges for serum TTR concentration are 0.10 - 0.40 g / L.
It should be remembered, however, that these values may vary according to age, sex and instrumentation used in the analysis laboratory. For this reason, it is preferable to consult the ranges reported directly on the report.
High Transthyretin - Causes
An increase in transthyretin values may depend on the following conditions:
- Increased synthesis of TTR
- Using exogenous corticosteroids or taking anabolic steroids;
- Non-steroidal anti-inflammatory drug therapy;
- Insulin-like growth factor 1 (IGF-1) exogenous or endogenous.
- Reduced catabolism of TTR
- Chronic renal failure;
- Renal tubular damage.
- Altered distribution
- Orthostatic position before blood sampling;
- Acute dehydration.
TTR levels can increase during Hodgkin's disease, hyposideremia, pregnancy and hyperadrenalism.
Low Transthyretin - Causes
Low levels may be present due to the reduced synthesis of transthyretin, as occurs in the case of:
- Acute phase response (infection, inflammation, trauma, malignant neoplasm, etc.);
- Administration of IL-6;
- Exogenous or endogenous estrogens;
- Thyroid disorders (especially endemic goiter).
Decreased TTR concentrations can also be caused by:
- Age (childhood, elderly subjects)
- Altered distribution
- Increased vascular permeability;
- Ascites or pleural effusion
- Clinostatic position before blood sampling (for example: bedridden patients).
- Increased losses:
- Acute bleeding;
- Nephrotic syndrome;
- Some disorders of the digestive system (enteropathies, celiac disease, etc.).
How it is measured
The transthyretin test is a laboratory test that is performed on a blood sample taken from the patient's arm.
Preparation
For blood sampling, the patient must fast for at least 8-10 hours. During this period, a moderate amount of water is allowed.
Interpretation of Results
Transthyretin testing may be required when there is a suspicion that a patient may be at risk of malnutrition, such as during severe or chronic medical conditions, during hospitalization, or when on parenteral nutrition or hemodialysis.
Alterations of prealbumin are seen in severe infections, inflammation (autoimmune or otherwise), burns, trauma (including surgery), malignancies, and liver disease.
However, the plasma concentration of transthyretin is influenced by multiple factors. Although the test is recommended for screening for malnutrition and as an aid in determining the severity of a patient's state of discomfort, the sensitivity and specificity of its measurement are rather low.
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