What is alkaline phosphatase (ALP)?
Alkaline phosphatase (ALP) is an important enzyme found throughout the body including the intestines, kidneys, liver, bones, and in the placenta of pregnant women. However, the bone and liver contain the highest concentrations of ALP in the body because they are the organs that greatly manufacture the enzyme. ALP is needed in liver physiology and bone development. (1)
The blood contains ALP, which amount is maintained at a particular range of values. Gradual increase or decrease in blood ALP can indicate problems in the liver or bones. However, there are people that have high blood ALP but don’t have any liver or bone problems. They are children, adolescents, and pregnant women. Blood ALP is high in children and adolescents because their bones are growing. High blood ALP is natural to pregnant women because ALP is needed by the developing fetus. (2)
What is ALP blood test? When it is ordered?
ALP blood test measures blood alkaline phosphatase to detect liver and bone problems. It is ordered by the doctor if the patient has symptoms of liver or bone diseases.
The signs and symptoms of liver disease include itching, dark urine, light colored feces, jaundice, abdominal swelling and pain, nausea, vomiting, appetite loss, fatigue, and weakness. (2)
For bone disorders, signs and symptoms can include bone and/or joint pain, bone deformity, and increased frequency of fractures. (2)
ALP blood test is also ordered to monitor improvement in patients receiving medications for a particular liver or bone disease.
What is the normal range of blood alkaline phosphatase (ALP)?
The normal range of blood ALP in adults is 44 to 147 international units per liter (IU/L) according toMedline Plus Medical Encyclopedia. (3) However, according to WebMD the 30-126 IU/L is the normal range for adults and 30-300 IU/L for children. (4) The range can vary with gender and age, and from laboratory to laboratory. As discussed above, children, adolescents, and pregnant women have higher blood ALP. (3)
What does elevated alkaline phosphatase mean?
When the test results show that the patient has an elevated alkaline phosphatase, it means that either the liver is damaged or something is causing increased bone cell activity. ALP test does not tell which of the two (liver or bone) is causing increased ALP. To find out, the doctor orders more laboratory tests for the liver (e.g. bilirubin, aspartate aminotransferase (AST), GGT and alanine aminotransferase (ALT), 5-nucleotidase) and the bones (e.g. calcium and phosphate levels). (2)
If blood levels of bilirubin, AST, ALT, 5-nucleotidase, and GGT are high, ALP is coming from the liver. ALP is coming from the bone if calcium and phosphate levels in the blood are elevated. (2)
Liver problems that cause very high levels of blood ALP may include hepatitis, blockage of bile ducts, cirrhosis, gallstones, liver cancer, or cancer that has spread to the liver from another part of the body. (4)
Bone disorders that cause high levels of blood ALP can include Paget’s disease, rickets, osteomalacia, bone cancer, or cancer that has spread to the bone from another part of the body. Overeactive parathyroid gland (hyperthyroidism) and healing bone fracture can also elevate blood ALP. (4)
What causes low ALP levels?
Low ALP levels can be caused by certain disorders including hypophosphatasia, anemia, leukemia, enteritis, hypothyroididsm, osteoporosis, malnutrition, magnesium deficiency, achondroplasia, cretinism, and protein deficiency.
What drugs can affect blood ALP levels?
Certain drugs can affect blood ALP levels. The doctor usually instructs the patient to stop taking the medications hours/days before the test. Drugs that can increase or decrease ALP levels include antibiotics, allopurinol, anti-inflammatory drugs, contraceptives, arthritis drugs, diabetes medications, chlorpromazine, cortisone, male hormones, narcotic pain relievers, methyldopa, tranquilizers, propanolol, and tricyclic antidepressants. The patient should not stop taking these medications without first talking to his doctor. (3)
References and Further Reading
- ALP: Test Sample. Lab Test Online
- ALP: The Test. Lab Test Online
- ALP: MedlinePlus Medical Encyclopedia
- Alkaline Phosphatase. WebMD