What is ALP?
Alkaline phosphatase (ALP) is an enzyme found in several tissues including liver, bone, intestine, kidney, placenta and white blood cells. Damage to these tissues causes the release of ALP into the bloodstream. ALP in blood of healthy adults is mainly from the liver, with most of the rest coming from bones. Elevated blood ALP is commonly caused by live damages, bone disorders, bile duct and gallbladder diseases.
ALP is used as part of the liver panel to detect liver damages, blocked bile ducts, gallstones or bile duct tumor. It is also often used to detect any condition that affects bone growth or causes elevated activity of bone cells, including osteoporosis, cancers that have spread to the bones, Paget disease that causes malformed bones, or other bone conditions such as vitamin D deficiency. Moderately elevated ALP may indicate other diseases, such as congestive heart failure, ulcerative colitis, Hodgkin lymphoma, and certain bacterial infections.
Blood transfusion or heart bypass surgery may cause temporally low levels of ALP. Zinc deficiency may also cause lower ALP levels. Hypophosphatasia, a rare genetic disorder of bone metabolism, can cause severe, long-term low ALP levels.
The ALP test measures the total ALP levels in the blood. Increase of total ALP may result from ALP specific for certain tissues that can be identified by additional tests. For example, the bone alkaline phosphatase (BAP) is the bone-specific isoform of ALP. Isoenzyme analyses using electrophoresis can find out the source of the elevated ALP (liver, bone, obesity, kidney and cancer).
The normal range of ALP is from 20 to 140 units per liter (U/L) in some recommendations and 44-147 U/L in other recommendations. High levels of ALP are normally seen in pregnant women and in children undergoing growth.
ALP is one of the 10 variables used to quantify biological age with PhenoAge. The reference range for ALP, ALP values greater than 48 U/L are associated with a significantly increased all-cause mortality risk in a meta-analysis of 4 studies that include ~9 million adults. In another meta-analysis that included 24 studies and 147,634 subjects, lowest risk of all-cause death is found in people with ALP values ~50 U/L. Furthermore, mortality risk increases linearly up to 85 U/L and increases at a much greater rate for values greater than 85 U/L. There is evidence that lower ALP may be better within the normal range.
What are the risk factors for abnormal ALP?
Risk factors for elevated ALP include various liver diseases and bone disorders, drug and medicine, and other etiology such as diet, smoking, obesity and environmental toxins. Low blood ALP levels may be caused by a rare genetic disorder called hypophosphatasia that affects bones and teeth, malnutrition/protein deficiency which could be caused by celiac disease, a deficiency in certain vitamins or minerals such as zinc, or certain medications.
Once doctors identify the cause of elevated ALP, treatment for the cause can bring the ALP level to normal range. Doctors may recommend removal of certain medications that can cause elevated ALP levels such as birth control pills, anti-inflammatory drugs, narcotic drugs. There also preventive actions you can take to keep your liver and bones healthy and your ALP level within healthy range. These may include: