Blood chemistry panels usually include a total protein test, a measure of the concentration of protein in the liquid component of your blood. A low total protein level can occur for a variety of reasons that fall into the general categories of dilution, increased loss, decreased production and malnutrition. Slightly reduced blood protein often causes no symptoms but a markedly low level can lead to weakness, fatigue and leakage of fluid from your circulation into the soft tissues of your body, which you might notice as swelling in your feet, lower legs, hands and/or face.
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Your blood protein level might be low if it's diluted by extra liquid in your circulation. This dilution effect is similar to what happens when you put food coloring in water and then add more water. The amount of food coloring remains the same but it gets diluted by the additional water. Low blood protein caused by a dilution effect occurs normally during pregnancy, especially in the late second and third trimesters. It can also occur with congestive heart failure and other medical conditions that lead to fluid overload in the body.
Your body loses some protein each day, which is normally replaced by the protein in your diet. Medical conditions that lead to increased protein loss can lead to an abnormally low blood protein level. Nephrotic syndrome describes a type of kidney damage that leads to loss of large amounts of protein in the urine and an accompanying drop in blood protein -- commonly with swelling, or edema, of the hands, feet and face. This syndrome occurs with a variety of kidney diseases and medical conditions that damage the kidneys, such as diabetes and lupus.
Increased protein loss can also occur through the intestines, a condition known as protein losing enteropathy (PLE). More than 60 diseases can lead to PLE, according to a July 2017 Clinical and Experimental Gastroenterology review article. Some of the more common conditions that can cause PLE include Crohn disease, celiac disease and certain types of intestinal infections. It can also occur with certain types of cancer and AIDS, among other diseases.
Your liver produces the majority of protein in your blood. Diseases that damage the liver can lead to reduced protein production and a low total protein level. This most often occurs in people with cirrhosis, a condition in which the liver is severely scarred. The most common diseases that can lead to cirrhosis and reduced protein production include alcoholic hepatitis, nonalcoholic fatty liver disease, and chronic hepatitis B or C infection.
Your digestive system breaks down the proteins you eat into constituent building blocks called amino acids. These building blocks are then used to make new proteins that your body needs. A diet with an inadequate amount of protein, impaired digestion and/or absorption of dietary proteins, and increased demand for proteins due to an illness or serious injury can lead to protein malnutrition -- insufficient protein to meet the body's needs. In addition to a low blood protein level, people with protein malnutrition frequently experience weight loss, lack of energy and loss of muscle tissue. Some of the many diseases and conditions that can lead to protein malnutrition include:
- Eating disorders
- Low-protein diet
- Celiac disease
- Inflammatory bowel disease
- Cystic fibrosis
- Pancreatic disease
- Gastric bypass surgery