Albumin: what it is and what functions it has in the human body

Blood is a liquid connective tissue that circulates through the vessels and capillaries, veins and arteries of all vertebrate animals. Humans have about 5 liters of blood on average in the body, and our hearts pump about 70 milliliters for each beat, which is almost all of it in the whole body in a single minute.

The blood, in addition to the red blood cells which give it color, is also the carrier of many other molecules with various physiological functions. This is the case with blood or plasma proteins, which are responsible for transporting lipids, hormones, vitamins, minerals and various immune-related actions.

In the following lines we will collect the characteristics of the most widespread and, surely, the most important blood protein. Stay with us, cause this time we’re dissecting the secrets involved in albumin and its medical implications.

    What is albumin?

    Albumin is a small, relatively symmetrical protein found in multiple structures of animal origin: blood, milk, egg white and the seeds of certain plants. In humans, it represents 54.3% of plasma proteins, that is to say it is the most abundant of all (3.5-5 g / dl).

    It might sound a little strange to say that albumin is the most abundant plasma protein, because we are all used to thinking of hemoglobin as the queen of blood proteins, right ?. It is curious to know that hemoglobin is not taken into account in this group because it is transported in red blood cells and not in plasma. Therefore, whatever its abundance inside these cell bodies (450 mg / ml), it is not conceived as a plasma protein per se.

    Below, we present a series of relevant data to contextualize the importance of albumin in the human body:

    • The liver produces 9 to 12 grams per day of this complex substance.
    • About 60% of albumin is found in the extravascular space, that is, outside the blood vessels.
    • Due to its intense negative charge, albumin is a water soluble protein.
    • Its life cycle in the bloodstream is 12 to 20 days.
    • Its renewal rate is 15 grams per day. Unlike other substances, there is no reserve of albumin in the human body.

    The most important function of albumin is the regulation of oncotic pressure, Necessary for the proper distribution of fluids in and out of tissues. Let us dwell for a moment on this unique term, because it is of great medical and biological interest.

      Albumin and its functions

      Oncotic pressure is defined, medically, as the osmotic pressure of a colloidal dissolution or dispersion. The difference between receiving this data and not knowing anything is small, which is why we offer a little nicer sense to the general public: it is a type of osmotic pressure caused by the difference in plasma proteins between blood plasma (in blood vessels) and interstitial fluid (Space between cells, one sixth of body tissue).

      Since blood capillaries are not very permeable to large plasma proteins (such as albumin), they are usually kept inside the plasma instead of being distributed through the interstitium. Due to this gradient in protein concentration (higher in the blood than in the interstitial fluid), water enters the blood vessels seeking to “balance” this difference. In short, we can say that this event maintains the correct distribution of bodily fluids in our body and allows their movement.

      However, maintaining oncotic pressure by its mere presence in plasma is not the only function of albumin. Among many others, we can list the following:

      • It facilitates the metabolism and detoxification of various substances, such as bilirubin, metals, ions or enzymes.
      • It promotes the elimination of free radicals, harmful products generated during cellular respiration.
      • It carries thyroid and fat soluble hormones.
      • It contains free fatty acids and unconjugated bilirubin, in addition to many other substances.
      • Controls the pH.

      What is the blood albumin test?

      As redundant as it may seem, it should be noted that the blood albumin test measures the amount of albumin in the patient’s blood. It is a measurable quantification of liver function, as synthesized in the liver, providing information on its condition and function.

      On the other hand, a low level of albumin in the blood can also indicate kidney failure, since in these cases this protein is excreted in the urine when it should not (event known as albuminuria). A healthy kidney does not allow albumin to pass from the blood into the urine.

      This test is generally recommended for patients going to the clinic for jaundice or yellowing of the skin (increased concentration of bilirubin in the tissues), weight loss, fatigue, dark urine, or pain under the right rib, the location of the liver.

      Normal serum albumin concentration is 3.5 to 5 grams per deciliter. A lower than normal value is known as hypoalbuminemia and can indicate any of the following disorders which we briefly summarize in the following lines.

      1. Cirrhosis of the liver

      This condition is the final consequence of a previous pathology in which the liver cells were destroyed, which resulted in their replacement with scar tissue, reducing the efficiency of the organ itself.

      The World Health Organization (WHO) estimates that 27,000 people die each year in high-income countries from this disease which, unsurprisingly, is linked to chronic alcoholism. Cirrhosis of the liver is not the only condition caused by alcoholism, as it is estimated that over 5% of all deaths worldwide are due to its consumption (no more and no less than 3,000,000).

      2. Malnutrition

      More than 462 million people in the most disadvantaged areas of the planet show signs of insufficient food. Hypoalbuminemia is one of them, as it occurs due to a lack of protein intake.

      Albumin is synthesized in the liver from amino acids obtained through the metabolism of food proteins.This is why the low values ​​of the same malnutrition already of the patient are clearly linked.

      3. Other causes

      While malnutrition and cirrhosis of the liver are often the most common causes of blood albumin deficiency, there are many other conditions that lead to it.. To introduce today’s topic, we present some of the most relevant:

      • Some type of kidney dysfunction, such as kidney infection.
      • Liver cancer. More than 800,000 people are diagnosed with this disease each year.
      • Congestive heart failure or pericarditis.
      • Stomach problems, such as lymphoma or inflammatory bowel disease (IBD). This is usually accompanied by nausea, vomiting, and diarrhea.
      • As a side effect of other diseases or of taking certain medications.

      It should be noted that in patients with hypoalbuminemia may consider administering albumin for medical purposes. Its dose and rate of administration depend on the individual’s conditions, which include blood pressure, pulse, hemodynamic status, hemoglobin and hematocrit concentrations, plasma protein content (the oncotic pressure described below). above) and the degree of venous and pulmonary congestion. . A total of 125 grams of albumin can be administered every 24 hours.


      As we have seen in this space, albumin it is the most common protein in blood plasma and performs multiple functions: From the transport and metabolism of various substances to the maintenance of oncotic pressure, this molecule is essential for the good physiological balance of the organism.

      Whether due to excessive excretion by the kidneys or poor hepatic synthesis, a lack of serum albumin can lead to swelling in certain areas of the body, fatigue, muscle weakness and many other clinical signs. . Although this condition can be caused by many events, alcoholism and malnutrition are two of the most common. Once again, we see that every particle that makes up our body is essential for maintaining the physiology and functions of our body.

      Bibliographical references:

      • Albumin (in blood), mHealth.
      • Albuminuria, NIDDK.
      • Hankins, J. (2008). Function of albumin in water balance. Nursing (Ed. Catalana), 26 (10), 42-43.
      • Hypoalbuminemia,
      • Oncotic pressure, University of Navarre clinic.

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