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Alkaline Phosphatase (ALP)

Generality

Serum alkaline phosphatase (ALP) determination is used in the diagnosis of skeletal and liver diseases .

ALP is an enzyme, a marker of bone formation located on the plasma membrane of osteoblasts (cells of the body responsible for the synthesis of bone tissue).

What's this

Alkaline phosphatase (or ALP, which stands for "alkaline phosphatase level") is an enzyme found in various tissues of the body. In particular, the ALP is found abundantly in the bones and liver .

Although in lower concentrations, alkaline phosphatase is also present in intestinal cells, kidneys and placenta of pregnant women.

The dosage of the alkaline phosphatase is performed to determine the levels in the circulation. This allows the screening or monitoring of bone diseases or hepato-biliary diseases, as well as assessing whether current therapies are effective.

Why do you measure

The alkaline phosphatase (ALP) test allows to measure its concentration in the blood.

This investigation is used to diagnose liver disease (especially biliary tract) and bone, monitor its progression or evaluate the efficacy of a therapeutic treatment.

The doctor prescribes the ALP test:

  • As part of routine liver function tests (bilirubin, transaminases AST and ALT);
  • When the patient has symptoms of a liver disorder (weakness, loss of appetite, nausea, vomiting, abdominal swelling and / or pain, jaundice, dark urine and clear stools etc.) or bone (pain in the bones and / or joints, deformations and predisposition to fractures).

When is it indicated?

Alkaline phosphatase measured in the blood comes mainly from the bones and the liver. For this reason, its dosage serves to identify some pathological conditions of the skeleton, or to clarify the nature of some liver diseases.

In the laboratory, it is possible to differentiate different components of alkaline phosphatase ( isoenzymes ): this is useful in situations where it is necessary to check whether any increase in the enzyme in the blood derives from the liver or bones. For this reason, in the report, the exam can also appear under the name of "ALP Isoenzimi".

Normal values

Normal values ​​of alkaline phosphatase:

  • Children up to 1 year: from 110 to 700 units per liter of blood (U / L);
  • Children from 1 to 10 years: from 110 to 550 U / L;
  • Children from 10 to 15 years: from 130 and 700 U / L;
  • Adults: from 50 to 220 U / L.

In any case, it should be remembered that the reference intervals of this and other clinical analyzes may be different depending on the method used.

ALP High - Causes

High values ​​of alkaline phosphatase are recorded in different pathological conditions, especially in the presence of diseases with high bone turnover, such as:

  • Paget's disease;
  • Osteomalacia (hypovitaminosis D);
  • Osteomyelitis;
  • hyperparathyroidism;
  • Bone metastases;
  • Osteoporosis.

The alkaline phosphatase values ​​are particularly high even in two physiological conditions :

  • In the child, especially during periods of rapid growth ;
  • During the second half of pregnancy .

In the pregnant woman, a particularly high increase in alkaline phosphatase may however take on pathological significance (gravidic jaundice).

Alkaline phosphatase also increases during the healing process of bone fractures and after menopause, an age in which the danger of osteoporosis becomes more concrete.

For what has been said so far, the dosage of the alkaline phosphatase is particularly useful, in addition to the diagnosis, also in the monitoring of the diseases listed above and in the evaluation of the therapeutic response.

Alkaline phosphatase values ​​also increase significantly in some liver diseases, such as in the presence of:

  • Jaundice from hepato-biliary stasis;
  • Calculations;
  • Cirrhosis;
  • Acute hepatitis;
  • Primitive and secondary neoplasms.

In the blood, to the alkaline phosphatases of bone derivation - which represent the most important part - are flanked by those of hepatic origin (in similar proportions) and renal (in clearly inferior proportions); are also known further isoforms produced by the intestine (in 25% of subjects), by the placenta (in the second half of pregnancy) and by leukocytes.

In some pathological conditions, moreover, anomalous fractions of alkaline phosphatases can appear, such as the isoenzymes Regan, Nagao, Kasahara, produced by some malignant tumors.

According to what has been said, increases in serum alkaline phosphatase can be recorded even in the presence of intestinal diseases, such as:

  • Hemorrhagic rectocolitis;
  • Chronic diarrhea.

Today it is possible to differentiate in the laboratory the different isoforms of the alkaline phosphatase: this procedure can be useful in situations where it is necessary to verify if the possible increase of the enzyme in the blood derives from the liver, bones or placenta

. The dosage of alkaline phosphatase is usually integrated with other tests, for example bilirubin, transaminases AST and ALT if liver function is to be monitored.

ALP Low - Causes

Rare and insignificant are the conditions in which the values ​​of alkaline phosphatase are lower than the norm.

Low ALP could be recorded in patients in old age or suffering from:

  • Anemia;
  • States of malnutrition;
  • Protein deficiency;
  • Zinc deficiency;
  • Menopause;
  • After a blood transfusion or heart bypass surgery;
  • Wilson's disease (altered copper metabolism);

More rarely, low values ​​of alkaline phosphatase are indicative of more serious problems, such as:

  • Hypophosphatasia (rare genetic disease affecting bone metabolism);
  • Placental insufficiency;
  • Kidney problems (nephritis);
  • Hypothyroidism;
  • Celiac disease (gluten intolerance);
  • Hypervitaminosis D;
  • Cystic fibrosis.

How to measure it

The examination of the alkaline phosphatase is performed with a normal collection of peripheral blood from the vein of an arm.

Preparation

Before undergoing blood sampling, a fast of at least 8-10 hours must be observed for the alkaline phosphatase test. During this period, it is possible to take only a small amount of water.

Drugs that can distort alkaline phosphatase levels should be discontinued within 72 hours of collection. Also, before the exam, you must be in an upright position for at least 30 minutes.

Interpretation of Results

Usually, ALP results are evaluated along with other liver and bone tests.

Only the doctor - through an accurate analysis of the patient's clinical condition - can understand what the abnormalities found in the amount of alkaline phosphatase present in the body are due to.

  • Levels of alkaline phosphatase "physiologically" higher than normal are found in pregnant women, children and adolescents in the growth phase and after menopause.
  • In general, higher than normal ALP levels are a sign of liver or bone disease.
    • If the other liver function tests - such as bilirubin and transaminases (AST and ALT) - are also elevated, alkaline phosphatase may indicate the presence of certain disorders affecting the liver (such as biliary carcinoma, liver metastasis, hepatitis or cirrhosis). In particular, in the case of bile duct obstruction, ALP and bilirubin increase more than transaminases.

    • When calcium and phosphate also increase along with alkaline phosphatase, it is more likely that the disorder affects the skeletal system . Bone diseases associated with increased alkaline phosphatase include: Paget's disease, bone metastases, deforming arthritis, osteomyelitis, rickets, sarcoidosis or fractures that have not yet completely healed. However, it is worth remembering that to reach this type of diagnosis alterations of other values ​​must be found in specific examinations, visits and instrumental investigations.

    • An increase in alkaline phosphatase levels may occur in certain situations, such as in the case of eclampsia (complication of pre-eclampsia or gestosis).
    • Moderate increases in ALP can be caused by other diseases such as: hyperparathyroidism, leukemia, Hodgkin's lymphoma, congestive heart failure, ulcerative colitis and some types of infections, such as mononucleosis.
    • An increase in alkaline phosphatase can also be caused by a high protein diet.
  • A decrease in alkaline phosphatase values may be linked to anemia, celiac disease (gluten intolerance) and kidney problems. Furthermore, a reduction of the parameter is observed in hypothyroidism and in old age.

Factors affecting the ALP

The values ​​of alkaline phosphatase can be altered by an incorrect diet, in particular by an excessive intake of fat or by the lack of calcium and vitamin D (which alters the metabolism of the bone).

ALP levels can also be affected by taking drugs such as ACE inhibitors, antibiotics, antiepileptics, estrogens and non-steroidal anti-inflammatory drugs (NSAIDs).

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