Alkaline Phosphatase (ALP): Why It’s High or Low (& Normal Ranges)

What is it :

Alkaline phosphatase is an enzyme that is present in may different body tissues. It is found in high levels in biliary duct cells, where bile from the liver is transferred to the intestines. It is also concentrated in the bones, as it is produced as as a result of bone formation and maintenance processes. 

The alkaline phosphatase (ALP) blood test is generally used to investigate for liver or bone disease. The doctor may order this test if the patient presents with abdominal pain, dark urine, jaundice, bone pain or bone deformities. It is often completed with other blood tests for assessment purposes. 

ALP is also found in the placenta, kidneys and intestines, although in lower levels. ALP levels may also rise with pregnancy or kidney disease. 

What causes abnormal ALP levels?

ALP testing can be used to evaluate liver or bone disease. Results can be interpreted as follows: 

1. High ALP levels

Alkaline phosphate can be high with liver diseases like: 

• Biliary duct obstruction, due to gallstones or cancer, which can interfere with bile flow from the liver to the intestines. 
• Hepatitis, which is a liver inflammation that can be caused by bacteria, virus and toxic substances 
• Cirrhosis, which is an illness that leads to liver destruction 
• Fatty diet, rich in foods like sugar, fried foods, red meat, butter and whole-fat diary 
• Kidney failure, particularly in people with chronic kidney disease 

Alkaline phosphatase levels can also be high in conditions that cause high bone cells productions, like certain types of bone cancer of Paget’s disease. This particular condition is characterized by abnormal bone growth in specific areas of the body. 

Some mild elevation can be noted with bone fracture healing, pregnancy, AIDS, intestinal infections, hyperthyroidism, Hodgkin’s lymphoma or even following a high-fat meal. 

2. Low ALP levels 

Abnormally low ALP levels is very rare, although several health conditions can cause decreases, such as: 

• Hypophosphatasia, which is a genetic disease that causes bone fractures and deformities
• Malnutrition
• Magnesium deficiency 
• Hypothyroidism 
• Severe diarrhea 
• Severe anemia 

Some medication, like birth control and hormone replacement therapy can also cause a mild decrease in ALP. 

When it’s indicated

Alkaline phosphatase testing should be ordered if the patient presents with signs or symptoms of liver disease. Some symptoms that may prompt testing include increased abdominal size, right-sided abdominal pain, jaundice, dark urine, pale stools and generalized itching. 

This test is also indicated for patients with signs or symptoms of bone issues, like generalized bone pain, bone deformities and bone fractures. 

How it’s tested

The test is completed in a lab setting, where a health care professional will draw 5 mL of draw from a vein in the arm. The blood sample is then placed in a closed container for further analysis. 

Normal ranges

Reference ranges will vary with age and the patient’s rate of growth: 

Children and adolescents

• < 2 years old:  85 - 235 U/L
• 2 to 8 years old:  65 - 210 U/L
• 9 to 15 years old::  60 - 300 U/L
• 16 to 21 years old::  30 - 200 U/L

Adults:

• 46 a 120 U/L 

With pregnancy, ALP levels can become slightly elevated due to fetal growth and due to the placenta.

The doctor may opt to order other liver function tests along with ALP, like AST, ALT, GGT and bilirubin tests, as well as imaging or even a livery biopsy.