What Is an Alkaline Phosphatase Level Test?
An alkaline phosphatase level test (ALP test) measures the amount of alkaline phosphatase enzyme in your bloodstream. The test requires a simple blood draw and is often a routine part of other blood tests.
Abnormal levels of ALP in your blood most often indicate a problem with your liver and/or bones. However, they may also indicate malnutrition, kidney tumors, or a serious infection. The normal range of ALP varies from person to person and depends on your age, blood type, and sex.
What Is Alkaline Phosphatase?
Alkaline phosphatase is an enzyme found in your bloodstream. ALP helps break down proteins in the body and exists in different forms, depending on where it originates. It is mostly produced in your liver, but some is also made in your bones, intestines, and kidneys. In pregnant women, ALP is made in the placenta.
Why Take an Alkaline Phosphatase Level Test?
An ALP test may be performed to determine how well your liver is functioning or to identify problems with your bones.
Checking ALP levels in the blood is a routine part of a liver function test used to determine if your liver is diseased or damaged. Symptoms such as jaundice (yellowing of the skin and eyes), abdominal pain, vomiting, and nausea may lead your doctor to suspect there is something wrong with your liver or gallbladder.
The ALP test can be helpful in identifying conditions such as:
- hepatitis (inflammation or infection of the liver)
- cirrhosis (scarring of the liver)
- cholescystitis (inflammation of the gallbladder)
- blockage of bile ducts (from gallstone, inflammation, or cancer)
You may also need an ALP test if you are taking a medication that has the potential to damage your liver, such as acetaminophen (Tylenol). Measuring ALP is one way to check for that damage.
The ALP test can be helpful in the diagnosis of bone problems such as:
- rickets: weakening of bones due to deficiency of calcium, phosphate, or vitamin D
- osteomalacia: softening of the bones due to vitamin D deficiency or the body’s inability to break down the vitamin properly
- Paget’s disease: disorder causing major problems with bone destruction and regrowth
ALP testing can also be helpful in investigating vitamin D deficiency, the presence of tumors, or unusual bone growth. It can also be used to check the progress of treatment for any of the above conditions.
How Should I Prepare for the Test?
Having blood drawn for an ALP test is routine, and you will most likely not need to do anything to prepare ahead of time. If the results of the test are inconclusive, your doctor may order a follow-up test. In this case, you will probably be asked to fast for 10 hours before the test.
Eating can interfere with your ALP levels. Medications can also change your ALP levels, so be sure to tell your doctor about all medicines you are taking.
How Is the Test Administered?
An ALP test requires a health professional to draw a small sample of blood from your arm. This will be done in your doctor’s office or a clinical lab. The doctor or nurse will clean the skin on the inside of your elbow with an antiseptic and apply an elastic band to allow blood to fill the vein. He or she will then insert a needle into the vein to draw blood into a small tube. The process is quick and causes little pain or discomfort.
What Are the Risks of an Alkaline Phosphatase Level Test?
There are very few risks associated with having your blood drawn. You may experience some bruising around the puncture site, but this can be avoided by putting pressure on the wound. In rare cases, phlebitis (inflammation of the vein) may develop. If you experience this complication, apply a warm compress until the swelling goes down. Inform your doctor before your blood is taken if you have any bleeding disorders.
What Do the Test Results Mean?
When the results of your ALP test are in, your doctor will discuss them with you and tell you what to do next. According to Cigna, the normal levels for an adult are between 25 and 100 units of ALP per liter of blood. The normal value for a child is up to 350 units per liter (Cigna, 2010). In pregnant women, the value may rise due to the ALP produced in the placenta.
Higher-than-normal levels of ALP in your blood may indicate a problem with your liver. This could include hepatitis (infection), cirrhosis (scarring), liver cancer, gallstones, or a blockage in your bile ducts.
High levels may also indicate an issue related to the bones such as rickets, Paget’s disease, bone cancer, or an overactive parathyroid gland. In rarer cases, high ALP levels can indicate heart failure, kidney cancer, mononucleosis, or a blood infection.
Having lower-than-normal ALP levels in your blood is rare, but can indicate malnutrition, which could be caused by celiac disease or a deficiency in vitamins and minerals.