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. Human beings have about 5 liters of blood in the body on average, and our heart pumps about 70 milliliters for each beat, that is, almost all of the present in the entire organism in a single minute.

Blood, in addition to the red blood cells that give it its color, also carries with it many other molecules with diverse physiological functions. This is the case of blood or plasma proteins, which are responsible for the transport of lipids, hormones, vitamins, minerals and various actions of an immunological nature.

In the following lines we will collect the characteristics of the most prevalent blood protein and, surely, the most important. Stay with us, because this time we dissect the secrets involved in albumin and its medical implications.

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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, it is the most abundant of all (3.5-5 g/dl).

It may sound a bit strange to say that albumin is the most abundant plasma protein, since all We are used to conceiving hemoglobin as the queen of blood proteins, right? It is curious to know that hemoglobin is not considered in this group since it is transported within the red blood cells, not in the plasma. For this reason, no matter how abundant it is inside these cell bodies (450 mg/ml), it is not conceived as a plasmatic 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 a day of this complex substance.
• Approximately 60% of albumin is located in the extravascular space, that is, outside the blood vessels.
• Because of its strong negative charge, albumin is a water-soluble protein.
• Its life cycle in the blood circulation is 12 to 20 days.
• Its renewal rate is 15 grams per day. Unlike other substances, there are no reserves of albumin in any part of 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 the tissues. We are going to stop for a moment in this singular term, because it is of great medical and biological interest.

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Albumin and its functions

Oncotic pressure is defined, medically, as the osmotic pressure of a colloidal solution or dispersion. The difference between receiving this information and not knowing anything is small, which is why we offer a slightly kinder meaning for the general public: it is about a type of osmotic pressure caused by the difference in plasma proteins between blood plasma (within blood vessels) and interstitial fluid (space between cells, one sixth of body tissues).

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

Even so, the maintenance of oncotic pressure simply by its presence in the 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.
• Potentiates the elimination of free radicals, harmful products generated during cellular respiration.
• Transports thyroid and fat-soluble hormones.
• It transports free fatty acids and unconjugated bilirubin, in addition to many other substances.
• Control the pH.

What is the blood albumin test?

As redundant as it may sound, it is necessary to clarify that the blood albumin test measures the amount of albumin in the patient's blood. It is a measurable quantification of liver function, since it is synthesized in the liver, it provides information on its state and functioning.

On the other hand, a low level of albumin in the blood can also be indicative of kidney function failures, because in these cases this protein is excreted in the urine when it should not (event known as albuminuria). A healthy kidney in no case allows albumin to pass from the blood into the urine.

In general, this test is usually recommended for patients who come to the clinic for jaundice or yellowing of the skin (increased concentration of of bilirubin in the tissues), weight loss, tiredness, dark colored urine or pain under the right rib, the location of the liver.

The normal serum albumin concentration is 3.5 to 5 grams per deciliter.. A value lower than normal is known as hypoalbuminemia and may indicate one of the following disorders that we briefly summarize in the following lines.

1. Hepatic cirrhosis

This condition is the final consequence of a previous pathology in which the liver cells have gone destroying, which has caused it to be replaced by scar tissue, reducing the effectiveness of the organ itself same.

The World Health Organization (WHO) estimates that 27,000 people die annually in high-income countries from this condition which, to no one's surprise, is linked to chronic alcoholism. Cirrhosis of the liver is not the only condition that generates alcoholism, since it is estimated that more than 5% of all deaths in the world are due to its consumption (neither more nor less than 3,000,000).

2. Malnutrition

More than 462 million people spread across the most disadvantaged areas of the planet show signs of nutritional insufficiency. 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 due to the metabolism of dietary proteins., reason for which its low values ​​and malnutrition of the patient are clearly linked.

3. other causes

Although malnutrition and liver cirrhosis are usually the most common causes of a lack of albumin in the blood, there are many other conditions that cause it.. We present, to close today's topic, some of the most relevant:

• Some type of kidney dysfunction, such as a kidney infection.
• Liver cancer. More than 800,000 people are diagnosed with this condition annually.
• Congestive heart failure or pericarditis.
• Stomach problems, such as lymphomas or Inflammatory Bowel Disease (IBD). This is usually accompanied by nausea, vomiting and diarrhea.
• As a side effect of other diseases or the intake of certain drugs.

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

Summary

As we have seen in this space, albumin It is the protein most present 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 correct physiological balance of the organism.

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

Bibliographic references:

• Albumin (in blood), Mhealth.
• Albuminuria, NIDDK.
• Hankins, J. (2008). Role of albumin in fluid balance. Nursing (Spanish ed.), 26(10), 42-43.
• Hypoalbuminemia, chemocare.com.
• Oncotic pressure, University of Navarra Clinic.