What are alkaline phosphatases, ALP?

What is ALP – Alkaline Phosphatase?

Alkaline phosphatase (ALP) is an enzyme found in several organs of the body, including the small intestine, kidneys, bile ducts, osteoblasts in the skeleton and in the placenta. In adults, the activity in plasma mainly originates from the bile ducts.

Why is ALP analyzed?

Alkaline phosphatase is one of several markers used to check liver values. It is mainly used to investigate liver cell damage and follow-up of liver disease. In various skeletal diseases, greatly elevated values can be seen.

What can high levels of ALP be due to?

Elevated levels of alkaline phosphatase (ALP) can be a sign of diseases that affect the skeleton, liver or biliary tract. ALP is an enzyme that is mainly produced in the liver, bones and placenta (during pregnancy), which means that elevated ALP levels can have several different causes.

Skeletal diseases

ALP rises in the following conditions that affect bone tissue:

Osteitis deformans (Paget's disease) which is a disease in which bone turnover is greatly increased, which in turn leads to deformities and elevated ALP levels.
Rickets and osteomalacia which are conditions caused by vitamin D deficiency, where bone mineralization is impaired and ALP may be elevated as a compensatory effect.
Skeletal metastases, cancer that spreads to the bones, can cause high ALP due to increased bone turnover.
Hyperparathyroidism, which involves overactivity of the parathyroid glands, can lead to increased bone resorption and thus high ALP levels.

Liver diseases and biliary obstruction

Since alkaline phosphatases are also produced in the liver, high levels can also be seen in:

Cholestasis (blockage of bile flow), in the case of gallstones or primary biliary cholangitis (PBC), impaired bile flow can lead to elevated ALP.
Liver cirrhosis and hepatitis, in these chronic liver diseases, ALP levels can be affected depending on the progression of the disease.
Tumors or metastases in the liver can cause elevated ALP values.

Pregnancy:

During pregnancy, especially in the third trimester, ALP can increase due to the production of placental phosphatase, which is a completely normal physiological change.

Other effects:

ALP can also be elevated in certain infections, inflammatory bowel disease, or the use of certain medications that affect liver or bone metabolism.

What can cause low levels of ALP?

Low levels of alkaline phosphatase (ALP) are uncommon; nutritional deficiencies, genetic conditions, or diseases that affect enzyme production are causes that may be linked to low values. It is important to remember that there are several factors that can affect ALP levels and that a low level is not always a cause for concern. Here are a few conditions where low levels of ALP can occur.

Hypophosphatasia

A rare, genetic condition in which ALP production is impaired, leading to problems with bone formation and mineralization. The severity varies from mild forms in adults to severe forms in children.

Nutritional deficiencies and metabolic factors

Zinc deficiency can lead to lower ALP levels as zinc is important for ALP production and maintenance of enzyme activity.
Magnesium deficiency can affect ALP and other enzymatic processes.
Protein deficiency or malnutrition can affect enzyme production and lower ALP due to low protein intake.

Endocrine diseases

Hypothyroidism (low thyroid hormone levels) can lower metabolism and thus ALP levels.
Cushing's syndrome, which is a condition with overproduction of cortisol, can affect ALP.